1
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Suetsugu S, Shimomura M, Kamimura M, Asaba T, Asaeda H, Kosuge Y, Sekino Y, Ikemori S, Kasahara Y, Kohsaka Y, Lee M, Yanase Y, Sakai H, Opletal P, Tokiwa Y, Haga Y, Matsuda Y. Fully gapped pairing state in spin-triplet superconductor UTe 2. Sci Adv 2024; 10:eadk3772. [PMID: 38324692 PMCID: PMC10849587 DOI: 10.1126/sciadv.adk3772] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2023] [Accepted: 01/05/2024] [Indexed: 02/09/2024]
Abstract
The recently discovered superconductor UTe2 is a promising candidate for spin-triplet superconductors, but the symmetry of the superconducting order parameter remains highly controversial. Here, we determine the superconducting gap structure by the thermal conductivity of ultraclean UTe2 single crystals. We find that the a-axis thermal conductivity divided by temperature κ/T in zero-temperature limit is vanishingly small for both magnetic field H‖a and H‖c axes up to H/Hc2 ∼ 0.2, demonstrating the absence of nodes around the a axis contrary to the previous belief. The present results, combined with the reduction of nuclear magnetic resonance Knight shift, indicate that the superconducting order parameter belongs to the isotropic Au representation with a fully gapped pairing state, analogous to the B phase of superfluid 3He. These findings reveal that UTe2 is likely to be a long-sought three-dimensional strong topological superconductor, hosting helical Majorana surface states on any crystal plane.
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Affiliation(s)
- Shota Suetsugu
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | | | | | - Tomoya Asaba
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - Hiroto Asaeda
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - Yuki Kosuge
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - Yuki Sekino
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - Shun Ikemori
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - Yuichi Kasahara
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - Yuhki Kohsaka
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - Minhyea Lee
- Department of Physics, University of Colorado Boulder, Boulder, CO 80309, USA
| | - Youichi Yanase
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - Hironori Sakai
- Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
| | - Petr Opletal
- Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
| | - Yoshifumi Tokiwa
- Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
| | - Yoshinori Haga
- Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
| | - Yuji Matsuda
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
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2
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Tokunaga Y, Sakai H, Kambe S, Opletal P, Tokiwa Y, Haga Y, Kitagawa S, Ishida K, Aoki D, Knebel G, Lapertot G, Krämer S, Horvatić M. Longitudinal Spin Fluctuations Driving Field-Reinforced Superconductivity in UTe_{2}. Phys Rev Lett 2023; 131:226503. [PMID: 38101342 DOI: 10.1103/physrevlett.131.226503] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2023] [Revised: 09/29/2023] [Accepted: 10/18/2023] [Indexed: 12/17/2023]
Abstract
Our measurements of ^{125}Te NMR relaxations reveal an enhancement of electronic spin fluctuations above μ_{0}H^{*}∼15 T, leading to their divergence in the vicinity of the metamagnetic transition at μ_{0}H_{m}≈35 T, below which field-reinforced superconductivity appears when a magnetic field (H) is applied along the crystallographic b axis. The NMR data evidence that these fluctuations are dominantly longitudinal, providing a key to understanding the peculiar superconducting phase diagram in H∥b, where such fluctuations enhance the pairing interactions.
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Affiliation(s)
- Y Tokunaga
- ASRC, Japan Atomic Energy Agency Tokai, Ibaraki 319-1195, Japan
| | - H Sakai
- ASRC, Japan Atomic Energy Agency Tokai, Ibaraki 319-1195, Japan
| | - S Kambe
- ASRC, Japan Atomic Energy Agency Tokai, Ibaraki 319-1195, Japan
| | - P Opletal
- ASRC, Japan Atomic Energy Agency Tokai, Ibaraki 319-1195, Japan
| | - Y Tokiwa
- ASRC, Japan Atomic Energy Agency Tokai, Ibaraki 319-1195, Japan
| | - Y Haga
- ASRC, Japan Atomic Energy Agency Tokai, Ibaraki 319-1195, Japan
| | - S Kitagawa
- Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | - K Ishida
- Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | - D Aoki
- IMR, Tohoku University, Ibaraki 311-1313, Japan
- Université Grenoble Alpes, CEA, Grenoble-INP, IRIG, Pheliqs, 38000 Grenoble, France
| | - G Knebel
- Université Grenoble Alpes, CEA, Grenoble-INP, IRIG, Pheliqs, 38000 Grenoble, France
| | - G Lapertot
- Université Grenoble Alpes, CEA, Grenoble-INP, IRIG, Pheliqs, 38000 Grenoble, France
| | - S Krämer
- Laboratoire National des Champs Magnétiques Intenses, LNCMI-CNRS (UPR3228), EMFL, Université Grenoble Alpes, UPS and INSA Toulouse, Boîte Postale 166, 38042 Grenoble Cedex 9, France
| | - M Horvatić
- Laboratoire National des Champs Magnétiques Intenses, LNCMI-CNRS (UPR3228), EMFL, Université Grenoble Alpes, UPS and INSA Toulouse, Boîte Postale 166, 38042 Grenoble Cedex 9, France
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3
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Ishihara K, Roppongi M, Kobayashi M, Imamura K, Mizukami Y, Sakai H, Opletal P, Tokiwa Y, Haga Y, Hashimoto K, Shibauchi T. Chiral superconductivity in UTe 2 probed by anisotropic low-energy excitations. Nat Commun 2023; 14:2966. [PMID: 37221184 DOI: 10.1038/s41467-023-38688-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2023] [Accepted: 05/08/2023] [Indexed: 05/25/2023] Open
Abstract
Chiral spin-triplet superconductivity is a topologically nontrivial pairing state with broken time-reversal symmetry, which can host Majorana quasiparticles. The heavy-fermion superconductor UTe2 exhibits peculiar properties of spin-triplet pairing, and the possible chiral state has been actively discussed. However, the symmetry and nodal structure of its order parameter in the bulk, which determine the Majorana surface states, remains controversial. Here we focus on the number and positions of superconducting gap nodes in the ground state of UTe2. Our magnetic penetration depth measurements for three field orientations in three crystals all show the power-law temperature dependence with exponents close to 2, which excludes single-component spin-triplet states. The anisotropy of low-energy quasiparticle excitations indicates multiple point nodes near the ky- and kz-axes in momentum space. These results can be consistently explained by a chiral B3u + iAu non-unitary state, providing fundamentals of the topological properties in UTe2.
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Affiliation(s)
- Kota Ishihara
- Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba, 277-8561, Japan.
| | - Masaki Roppongi
- Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba, 277-8561, Japan
| | - Masayuki Kobayashi
- Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba, 277-8561, Japan
| | - Kumpei Imamura
- Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba, 277-8561, Japan
| | - Yuta Mizukami
- Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba, 277-8561, Japan
- Department of Physics, Graduate School of Science, Tohoku University, 6-3, Aramaki Aza-Aoba, Aoba-ku, Sendai, 980-8578, Japan
| | - Hironori Sakai
- Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki, 319-1195, Japan
| | - Petr Opletal
- Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki, 319-1195, Japan
| | - Yoshifumi Tokiwa
- Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki, 319-1195, Japan
| | - Yoshinori Haga
- Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki, 319-1195, Japan
| | - Kenichiro Hashimoto
- Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba, 277-8561, Japan
| | - Takasada Shibauchi
- Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba, 277-8561, Japan.
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4
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Sakai H, Tokiwa Y, Opletal P, Kimata M, Awaji S, Sasaki T, Aoki D, Kambe S, Tokunaga Y, Haga Y. Field Induced Multiple Superconducting Phases in UTe_{2} along Hard Magnetic Axis. Phys Rev Lett 2023; 130:196002. [PMID: 37243663 DOI: 10.1103/physrevlett.130.196002] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/03/2022] [Revised: 12/19/2022] [Accepted: 04/04/2023] [Indexed: 05/29/2023]
Abstract
The superconducting (SC) phase diagram in uranium ditelluride is explored under magnetic fields (H) along the hard magnetic b axis using a high-quality single crystal with T_{c}=2.1 K. Simultaneous electrical resistivity and ac magnetic susceptibility measurements discern low- and high-field SC (LFSC and HFSC, respectively) phases with contrasting field-angular dependence. Crystal quality increases the upper critical field of the LFSC phase, but the H^{*} of ∼15 T, at which the HFSC phase appears, is always the same through the various crystals. A phase boundary signature is also observed inside the LFSC phase near H^{*}, indicating an intermediate SC phase characterized by small flux pinning forces.
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Affiliation(s)
- H Sakai
- Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
| | - Y Tokiwa
- Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
| | - P Opletal
- Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
| | - M Kimata
- Institute for Materials Research, Tohoku University, Sendai, 980-8577, Japan
| | - S Awaji
- High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
| | - T Sasaki
- Institute for Materials Research, Tohoku University, Sendai, 980-8577, Japan
| | - D Aoki
- Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313, Japan
| | - S Kambe
- Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
| | - Y Tokunaga
- Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
| | - Y Haga
- Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
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5
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Haga Y, Opletal P, Tokiwa Y, Yamamoto E, Tokunaga Y, Kambe S, Sakai H. Effect of uranium deficiency on normal and superconducting properties in unconventional superconductor UTe 2. J Phys Condens Matter 2022; 34:175601. [PMID: 35120343 DOI: 10.1088/1361-648x/ac5201] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2021] [Accepted: 02/04/2022] [Indexed: 06/14/2023]
Abstract
Single crystals of the unconventional superconductor UTe2have been grown in various conditions which result in different superconducting transition temperature as well as normal state properties. Stoichiometry of the samples has been characterized by the single-crystal x-ray crystallography and electron microprobe analyses. Superconducting samples are nearly stoichiometric within an experimental error of about 1%, while non-superconducting sample significantly deviates from the ideal composition. The superconducting UTe2showed that the large density of states was partially gapped in the normal state, while the non-superconducting sample is characterized by the relatively large electronic specific heat as reported previously.
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Affiliation(s)
- Y Haga
- Advanced Science Research Center, Japan Atomic Energy Agency, Japan
| | - P Opletal
- Advanced Science Research Center, Japan Atomic Energy Agency, Japan
| | - Y Tokiwa
- Advanced Science Research Center, Japan Atomic Energy Agency, Japan
| | - E Yamamoto
- Advanced Science Research Center, Japan Atomic Energy Agency, Japan
| | - Y Tokunaga
- Advanced Science Research Center, Japan Atomic Energy Agency, Japan
| | - S Kambe
- Advanced Science Research Center, Japan Atomic Energy Agency, Japan
| | - H Sakai
- Advanced Science Research Center, Japan Atomic Energy Agency, Japan
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6
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Bachus S, Kaib DAS, Tokiwa Y, Jesche A, Tsurkan V, Loidl A, Winter SM, Tsirlin AA, Valentí R, Gegenwart P. Thermodynamic Perspective on Field-Induced Behavior of α-RuCl_{3}. Phys Rev Lett 2020; 125:097203. [PMID: 32915615 DOI: 10.1103/physrevlett.125.097203] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2020] [Accepted: 07/28/2020] [Indexed: 06/11/2023]
Abstract
Measurements of the magnetic Grüneisen parameter (Γ_{B}) and specific heat on the Kitaev material candidate α-RuCl_{3} are used to access in-plane field and temperature dependence of the entropy up to 12 T and down to 1 K. No signatures corresponding to phase transitions are detected beyond the boundary of the magnetically ordered region, but only a shoulderlike anomaly in Γ_{B}, involving an entropy increment as small as 10^{-5}Rlog2. These observations put into question the presence of a phase transition between the purported quantum spin liquid and the field-polarized state of α-RuCl_{3}. We show theoretically that at low temperatures Γ_{B} is sensitive to crossings in the lowest excitations within gapped phases, and identify the measured shoulderlike anomaly as being of such origin. Exact diagonalization calculations demonstrate that the shoulderlike anomaly can be reproduced in extended Kitaev models that gain proximity to an additional phase at finite field without entering it. We discuss manifestations of this proximity in other measurements.
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Affiliation(s)
- S Bachus
- Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, Universitätsstr. 1, 86159 Augsburg, Germany
| | - D A S Kaib
- Institute of Theoretical Physics, Goethe University Frankfurt, Max-von-Laue-Strasse 1, 60438 Frankfurt am Main, Germany
| | - Y Tokiwa
- Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, Universitätsstr. 1, 86159 Augsburg, Germany
| | - A Jesche
- Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, Universitätsstr. 1, 86159 Augsburg, Germany
| | - V Tsurkan
- Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, Universitätsstr. 1, 86159 Augsburg, Germany
- Institute of Applied Physics, Chisinau MD-2028, Republic of Moldova
| | - A Loidl
- Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, Universitätsstr. 1, 86159 Augsburg, Germany
| | - S M Winter
- Institute of Theoretical Physics, Goethe University Frankfurt, Max-von-Laue-Strasse 1, 60438 Frankfurt am Main, Germany
| | - A A Tsirlin
- Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, Universitätsstr. 1, 86159 Augsburg, Germany
| | - R Valentí
- Institute of Theoretical Physics, Goethe University Frankfurt, Max-von-Laue-Strasse 1, 60438 Frankfurt am Main, Germany
| | - P Gegenwart
- Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, Universitätsstr. 1, 86159 Augsburg, Germany
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7
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Li Y, Bachus S, Liu B, Radelytskyi I, Bertin A, Schneidewind A, Tokiwa Y, Tsirlin AA, Gegenwart P. Rearrangement of Uncorrelated Valence Bonds Evidenced by Low-Energy Spin Excitations in YbMgGaO_{4}. Phys Rev Lett 2019; 122:137201. [PMID: 31012603 DOI: 10.1103/physrevlett.122.137201] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/23/2018] [Indexed: 05/02/2023]
Abstract
dc-magnetization data measured down to 40 mK speak against conventional freezing and reinstate YbMgGaO_{4} as a triangular spin-liquid candidate. Magnetic susceptibility measured parallel and perpendicular to the c axis reaches constant values below 0.1 and 0.2 K, respectively, thus indicating the presence of gapless low-energy spin excitations. We elucidate their nature in the triple-axis inelastic neutron scattering experiment that pinpoints the low-energy (E≤J_{0}∼0.2 meV) part of the excitation continuum present at low temperatures (T<J_{0}/k_{B}), but completely disappearing upon warming the system above T≫J_{0}/k_{B}. In contrast to the high-energy part at E>J_{0} that is rooted in the breaking of nearest-neighbor valence bonds and persists to temperatures well above J_{0}/k_{B}, the low-energy one originates from the rearrangement of the valence bonds and thus from the propagation of unpaired spins. We further extend this picture to herbertsmithite, the spin-liquid candidate on the kagome lattice, and argue that such a hierarchy of magnetic excitations may be a universal feature of quantum spin liquids.
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Affiliation(s)
- Yuesheng Li
- Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
| | - Sebastian Bachus
- Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
| | - Benqiong Liu
- Key Laboratory of Neutron Physics, Institute of Nuclear Physics and Chemistry, CAEP, Mianyang 621900, People's Republic of China
- Jülich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ), Forschungszentrum Jülich GmbH, Lichtenbergstrasse 1, 85748 Garching, Germany
| | - Igor Radelytskyi
- Jülich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ), Forschungszentrum Jülich GmbH, Lichtenbergstrasse 1, 85748 Garching, Germany
| | - Alexandre Bertin
- Institut fuer Festkörperphysik, TU Dresden, D-01062, Dresden, Germany
| | - Astrid Schneidewind
- Jülich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ), Forschungszentrum Jülich GmbH, Lichtenbergstrasse 1, 85748 Garching, Germany
| | - Yoshifumi Tokiwa
- Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
| | - Alexander A Tsirlin
- Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
| | - Philipp Gegenwart
- Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
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8
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Naritsuka M, Rosa PFS, Luo Y, Kasahara Y, Tokiwa Y, Ishii T, Miyake S, Terashima T, Shibauchi T, Ronning F, Thompson JD, Matsuda Y. Tuning the Pairing Interaction in a d-Wave Superconductor by Paramagnons Injected through Interfaces. Phys Rev Lett 2018; 120:187002. [PMID: 29775349 DOI: 10.1103/physrevlett.120.187002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/12/2017] [Indexed: 06/08/2023]
Abstract
Unconventional superconductivity and magnetism are intertwined on a microscopic level in a wide class of materials. A new approach to this most fundamental and hotly debated issue focuses on the role of interactions between superconducting electrons and bosonic fluctuations at the interface between adjacent layers in heterostructures. Here we fabricate hybrid superlattices consisting of alternating atomic layers of the heavy-fermion superconductor CeCoIn_{5} and antiferromagnetic (AFM) metal CeRhIn_{5}, in which the AFM order can be suppressed by applying pressure. We find that the superconducting and AFM states coexist in spatially separated layers, but their mutual coupling via the interface significantly modifies the superconducting properties. An analysis of upper critical fields reveals that, upon suppressing the AFM order by applied pressure, the force binding superconducting electron pairs acquires an extreme strong-coupling nature. This demonstrates that superconducting pairing can be tuned nontrivially by magnetic fluctuations (paramagnons) injected through the interface.
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Affiliation(s)
- M Naritsuka
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - P F S Rosa
- Los Alamos National Laboratory, Los Alamos, New Mexico 87544, USA
| | - Yongkang Luo
- Los Alamos National Laboratory, Los Alamos, New Mexico 87544, USA
| | - Y Kasahara
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - Y Tokiwa
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
- Center for Electronic Correlations and Magnetism, Institute of Physics, Augsburg University, 86159 Augsburg, Germany
| | - T Ishii
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - S Miyake
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - T Terashima
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - T Shibauchi
- Department of Advanced Materials Science, University of Tokyo, Chiba 277-8561, Japan
| | - F Ronning
- Los Alamos National Laboratory, Los Alamos, New Mexico 87544, USA
| | - J D Thompson
- Los Alamos National Laboratory, Los Alamos, New Mexico 87544, USA
| | - Y Matsuda
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
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9
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Sato Y, Kasahara S, Taniguchi T, Xing X, Kasahara Y, Tokiwa Y, Yamakawa Y, Kontani H, Shibauchi T, Matsuda Y. Abrupt change of the superconducting gap structure at the nematic critical point in FeSe 1-xS x. Proc Natl Acad Sci U S A 2018; 115:1227-1231. [PMID: 29363600 PMCID: PMC5819433 DOI: 10.1073/pnas.1717331115] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The emergence of the nematic electronic state that breaks rotational symmetry is one of the most fascinating properties of the iron-based superconductors, and has relevance to cuprates as well. FeSe has a unique ground state in which superconductivity coexists with a nematic order without long-range magnetic ordering, providing a significant opportunity to investigate the role of nematicity in the superconducting pairing interaction. Here, to reveal how the superconducting gap evolves with nematicity, we measure the thermal conductivity and specific heat of FeSe1 - x S x , in which the nematicity is suppressed by isoelectronic sulfur substitution and a nematic critical point (NCP) appears at [Formula: see text] We find that, in the whole nematic regime ([Formula: see text]), the field dependence of two quantities consistently shows two-gap behavior; one gap is small but highly anisotropic with deep minima or line nodes, and the other is larger and more isotropic. In stark contrast, in the tetragonal regime ([Formula: see text]), the larger gap becomes strongly anisotropic, demonstrating an abrupt change in the superconducting gap structure at the NCP. Near the NCP, charge fluctuations of [Formula: see text] and [Formula: see text] orbitals are enhanced equally in the tetragonal side, whereas they develop differently in the orthorhombic side. Our observation therefore directly implies that the orbital-dependent nature of the nematic fluctuations has a strong impact on the superconducting gap structure and hence on the pairing interaction.
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Affiliation(s)
- Yuki Sato
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | | | | | - Xiangzhuo Xing
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - Yuichi Kasahara
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - Yoshifumi Tokiwa
- Center for Electronic Correlations and Magnetism, Institute of Physics, Augsburg University, 86159 Augsburg, Germany
| | - Youichi Yamakawa
- Department of Physics, Nagoya University, Nagoya 464-8602, Japan
| | - Hiroshi Kontani
- Department of Physics, Nagoya University, Nagoya 464-8602, Japan
| | - Takasada Shibauchi
- Department of Advanced Materials Science, University of Tokyo, Chiba 277-8561, Japan
| | - Yuji Matsuda
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan;
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10
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Takenaka T, Mizukami Y, Wilcox JA, Konczykowski M, Seiro S, Geibel C, Tokiwa Y, Kasahara Y, Putzke C, Matsuda Y, Carrington A, Shibauchi T. Full-Gap Superconductivity Robust against Disorder in Heavy-Fermion CeCu_{2}Si_{2}. Phys Rev Lett 2017; 119:077001. [PMID: 28949698 DOI: 10.1103/physrevlett.119.077001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Indexed: 06/07/2023]
Abstract
A key aspect of unconventional pairing by the antiferromagnetic spin-fluctuation mechanism is that the superconducting energy gap must have the opposite sign on different parts of the Fermi surface. Recent observations of non-nodal gap structure in the heavy-fermion superconductor CeCu_{2}Si_{2} were then very surprising, given that this material has long been considered a prototypical example of a superconductor where the Cooper pairing is magnetically mediated. Here we present a study of the effect of controlled point defects, introduced by electron irradiation, on the temperature-dependent magnetic penetration depth λ(T) in CeCu_{2}Si_{2}. We find that the fully gapped state is robust against disorder, demonstrating that low-energy bound states, expected for sign-changing gap structures, are not induced by nonmagnetic impurities. This provides bulk evidence for s_{++}-wave superconductivity without sign reversal.
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Affiliation(s)
- T Takenaka
- Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba 277-8561, Japan
| | - Y Mizukami
- Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba 277-8561, Japan
| | - J A Wilcox
- H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, England
| | - M Konczykowski
- Laboratoire des Solides Irradiés, École Polytechnique, CNRS, CEA, Université Paris-Saclay, F-91128 Palaiseau, France
| | - S Seiro
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
- Institute for Solid State Physics, IFW-Dresden, Helmholtzstrasse 20, 01069 Dresden, Germany
| | - C Geibel
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
| | - Y Tokiwa
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
- Center for Electronic Correlations and Magnetism, Institute of Physics, Augsburg University, 86159 Augsburg, Germany
| | - Y Kasahara
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - C Putzke
- H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, England
| | - Y Matsuda
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - A Carrington
- H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, England
| | - T Shibauchi
- Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba 277-8561, Japan
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11
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Yamashita T, Takenaka T, Tokiwa Y, Wilcox JA, Mizukami Y, Terazawa D, Kasahara Y, Kittaka S, Sakakibara T, Konczykowski M, Seiro S, Jeevan HS, Geibel C, Putzke C, Onishi T, Ikeda H, Carrington A, Shibauchi T, Matsuda Y. Fully gapped superconductivity with no sign change in the prototypical heavy-fermion CeCu 2Si 2. Sci Adv 2017; 3:e1601667. [PMID: 28691082 PMCID: PMC5482556 DOI: 10.1126/sciadv.1601667] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/19/2016] [Accepted: 05/05/2017] [Indexed: 06/07/2023]
Abstract
In exotic superconductors, including high-Tc copper oxides, the interactions mediating electron Cooper pairing are widely considered to have a magnetic rather than a conventional electron-phonon origin. Interest in this exotic pairing was initiated by the 1979 discovery of heavy-fermion superconductivity in CeCu2Si2, which exhibits strong antiferromagnetic fluctuations. A hallmark of unconventional pairing by anisotropic repulsive interactions is that the superconducting energy gap changes sign as a function of the electron momentum, often leading to nodes where the gap goes to zero. We report low-temperature specific heat, thermal conductivity, and magnetic penetration depth measurements in CeCu2Si2, demonstrating the absence of gap nodes at any point on the Fermi surface. Moreover, electron irradiation experiments reveal that the superconductivity survives even when the electron mean free path becomes substantially shorter than the superconducting coherence length. This indicates that superconductivity is robust against impurities, implying that there is no sign change in the gap function. These results show that, contrary to long-standing belief, heavy electrons with extremely strong Coulomb repulsions can condense into a fully gapped s-wave superconducting state, which has an on-site attractive pairing interaction.
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Affiliation(s)
| | - Takaaki Takenaka
- Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba 277-8561, Japan
| | | | - Joseph A. Wilcox
- H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, UK
| | - Yuta Mizukami
- Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba 277-8561, Japan
| | - Daiki Terazawa
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - Yuichi Kasahara
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - Shunichiro Kittaka
- Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
| | - Toshiro Sakakibara
- Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
| | - Marcin Konczykowski
- Laboratoire des Solides Irradiés, École Polytechnique, CNRS, Commissariat à l’Energie Atomique et aux Energies Alternatives, Université Paris-Saclay, 91128 Palaiseau Cedex, France
| | - Silvia Seiro
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Strasse 40, 01187 Dresden, Germany
| | - Hirale S. Jeevan
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Strasse 40, 01187 Dresden, Germany
| | - Christoph Geibel
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Strasse 40, 01187 Dresden, Germany
| | - Carsten Putzke
- H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, UK
| | - Takafumi Onishi
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - Hiroaki Ikeda
- Department of Physics, Ritsumeikan University, Kusatsu 525-8577, Japan
| | - Antony Carrington
- H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, UK
| | - Takasada Shibauchi
- Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba 277-8561, Japan
| | - Yuji Matsuda
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
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12
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Tokiwa Y, Piening B, Jeevan HS, Bud’ko SL, Canfield PC, Gegenwart P. Super-heavy electron material as metallic refrigerant for adiabatic demagnetization cooling. Sci Adv 2016; 2:e1600835. [PMID: 27626073 PMCID: PMC5017822 DOI: 10.1126/sciadv.1600835] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/20/2016] [Accepted: 08/09/2016] [Indexed: 06/06/2023]
Abstract
Low-temperature refrigeration is of crucial importance in fundamental research of condensed matter physics, because the investigations of fascinating quantum phenomena, such as superconductivity, superfluidity, and quantum criticality, often require refrigeration down to very low temperatures. Currently, cryogenic refrigerators with (3)He gas are widely used for cooling below 1 K. However, usage of the gas has been increasingly difficult because of the current worldwide shortage. Therefore, it is important to consider alternative methods of refrigeration. We show that a new type of refrigerant, the super-heavy electron metal YbCo2Zn20, can be used for adiabatic demagnetization refrigeration, which does not require (3)He gas. This method has a number of advantages, including much better metallic thermal conductivity compared to the conventional insulating refrigerants. We also demonstrate that the cooling performance is optimized in Yb1-x Sc x Co2Zn20 by partial Sc substitution, with x ~ 0.19. The substitution induces chemical pressure that drives the materials to a zero-field quantum critical point. This leads to an additional enhancement of the magnetocaloric effect in low fields and low temperatures, enabling final temperatures well below 100 mK. This performance has, up to now, been restricted to insulators. For nearly a century, the same principle of using local magnetic moments has been applied for adiabatic demagnetization cooling. This study opens new possibilities of using itinerant magnetic moments for cryogen-free refrigeration.
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Affiliation(s)
- Yoshifumi Tokiwa
- I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
- Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
| | - Boy Piening
- I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany
| | - Hirale S. Jeevan
- I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany
| | - Sergey L. Bud’ko
- Ames Laboratory, U.S. Department of Energy, and Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA
| | - Paul C. Canfield
- Ames Laboratory, U.S. Department of Energy, and Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA
| | - Philipp Gegenwart
- I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany
- Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
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13
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Tokiwa Y, Mchalwat M, Perry RS, Gegenwart P. Multiple Metamagnetic Quantum Criticality in Sr_{3}Ru_{2}O_{7}. Phys Rev Lett 2016; 116:226402. [PMID: 27314732 DOI: 10.1103/physrevlett.116.226402] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2016] [Indexed: 06/06/2023]
Abstract
Bilayer strontium ruthenate Sr_{3}Ru_{2}O_{7} displays pronounced non-Fermi liquid behavior at magnetic fields around 8 T, applied perpendicular to the ruthenate planes, which previously has been associated with an itinerant metamagnetic quantum critical end point (QCEP). We focus on the magnetic Grüneisen parameter Γ_{H}, which is the most direct probe to characterize field-induced quantum criticality. We confirm quantum critical scaling due to a putative two-dimensional QCEP near 7.845(5) T, which is masked by two ordered phases A and B, identified previously by neutron scattering. In addition, we find evidence for a QCEP at 7.53(2) T and determine the quantum critical regimes of both instabilities and the effect of their superposition.
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Affiliation(s)
- Y Tokiwa
- I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - M Mchalwat
- I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany
| | - R S Perry
- London Centre for Nanotechnology, Faculty of Maths & Physical Sciences, University College London, London-WC1E 6BT, United Kingdom
| | - P Gegenwart
- I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany
- Experimentalphysik VI, Center for Electronic Correlations and Magnetism, Augsburg University, 86159 Augsburg, Germany
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14
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Ishii T, Toda R, Hanaoka Y, Tokiwa Y, Shimozawa M, Kasahara Y, Endo R, Terashima T, Nevidomskyy AH, Shibauchi T, Matsuda Y. Tuning the Magnetic Quantum Criticality of Artificial Kondo Superlattices CeRhIn_{5}/YbRhIn_{5}. Phys Rev Lett 2016; 116:206401. [PMID: 27258878 DOI: 10.1103/physrevlett.116.206401] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/10/2016] [Indexed: 06/05/2023]
Abstract
The effects of reduced dimensions and the interfaces on antiferromagnetic quantum criticality are studied in epitaxial Kondo superlattices, with alternating n layers of heavy-fermion antiferromagnet CeRhIn_{5} and seven layers of normal metal YbRhIn_{5}. As n is reduced, the Kondo coherence temperature is suppressed due to the reduction of effective Kondo screening. The Néel temperature is gradually suppressed as n decreases and the quasiparticle mass is strongly enhanced, implying dimensional control toward a quantum critical point. Magnetotransport measurements reveal that a quantum critical point is reached for the n=3 superlattice by applying small magnetic fields. Remarkably, the anisotropy of the quantum critical field is opposite to the expectations from the magnetic susceptibility in bulk CeRhIn_{5}, suggesting that the Rashba spin-orbit interaction arising from the inversion symmetry breaking at the interface plays a key role for tuning the quantum criticality in the two-dimensional Kondo lattice.
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Affiliation(s)
- T Ishii
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - R Toda
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - Y Hanaoka
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - Y Tokiwa
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
- Research Center for Low Temperature and Materials Science, Kyoto University, Kyoto 606-8501, Japan
| | - M Shimozawa
- Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan
| | - Y Kasahara
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - R Endo
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - T Terashima
- Research Center for Low Temperature and Materials Science, Kyoto University, Kyoto 606-8501, Japan
| | - A H Nevidomskyy
- Department of Physics and Astronomy, Rice University, 6100 Main Street, Houston, Texas 77005, USA
| | - T Shibauchi
- Department of Advanced Materials Science, University of Tokyo, Chiba 277-8561, Japan
| | - Y Matsuda
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
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15
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Tokiwa Y, Stingl C, Kim MS, Takabatake T, Gegenwart P. Characteristic signatures of quantum criticality driven by geometrical frustration. Sci Adv 2015; 1:e1500001. [PMID: 26601165 PMCID: PMC4640633 DOI: 10.1126/sciadv.1500001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/02/2015] [Accepted: 03/26/2015] [Indexed: 05/17/2023]
Abstract
Geometrical frustration describes situations where interactions are incompatible with the lattice geometry and stabilizes exotic phases such as spin liquids. Whether geometrical frustration of magnetic interactions in metals can induce unconventional quantum critical points is an active area of research. We focus on the hexagonal heavy fermion metal CeRhSn, where the Kondo ions are located on distorted kagome planes stacked along the c axis. Low-temperature specific heat, thermal expansion, and magnetic Grüneisen parameter measurements prove a zero-field quantum critical point. The linear thermal expansion, which measures the initial uniaxial pressure derivative of the entropy, displays a striking anisotropy. Critical and noncritical behaviors along and perpendicular to the kagome planes, respectively, prove that quantum criticality is driven be geometrical frustration. We also discovered a spin flop-type metamagnetic crossover. This excludes an itinerant scenario and suggests that quantum criticality is related to local moments in a spin liquid-like state.
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Affiliation(s)
- Yoshifumi Tokiwa
- I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany
- Corresponding author. E-mail:
| | - Christian Stingl
- I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany
- Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
| | - Moo-Sung Kim
- Department of Quantum Matter, Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashi-Hiroshima 739-8530, Japan
| | - Toshiro Takabatake
- Department of Quantum Matter, Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashi-Hiroshima 739-8530, Japan
| | - Philipp Gegenwart
- I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany
- Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
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16
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Tokiwa Y, Ishikawa JJ, Nakatsuji S, Gegenwart P. Quantum criticality in a metallic spin liquid. Nat Mater 2014; 13:356-359. [PMID: 24651428 DOI: 10.1038/nmat3900] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2013] [Accepted: 01/31/2014] [Indexed: 06/03/2023]
Abstract
When magnetic order is suppressed by frustrated interactions, spins form a highly correlated fluctuating 'spin liquid' state down to low temperatures. The magnetic order of local moments can also be suppressed when they are fully screened by conduction electrons through the Kondo effect. Thus, the combination of strong geometrical frustration and Kondo screening may lead to novel types of quantum phase transition. We report low-temperature thermodynamic measurements on the frustrated Kondo lattice Pr₂Ir₂O₇, which exhibits a chiral spin liquid state below 1.5 K as a result of the frustrated interaction between Ising 4f local moments and their interplay with Ir conduction electrons. Our results provide a first clear example of zero-field quantum critical scaling that emerges in a spin liquid state of a highly frustrated metal.
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17
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Tokiwa Y, Garst M, Gegenwart P, Bud'ko SL, Canfield PC. Quantum bicriticality in the heavy-fermion metamagnet YbAgGe. Phys Rev Lett 2013; 111:116401. [PMID: 24074108 DOI: 10.1103/physrevlett.111.116401] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/09/2012] [Indexed: 06/02/2023]
Abstract
Bicritical points, at which two distinct symmetry-broken phases become simultaneously unstable, are typical for spin-flop metamagnetism. Interestingly, the heavy-fermion compound YbAgGe also possesses such a bicritical point (BCP) with a low temperature T(BCP)≈0.3 K at a magnetic field of μH(BCP)≈4.5 T. In its vicinity, YbAgGe exhibits anomalous behavior that we attribute to the influence of a quantum bicritical point that is close in parameter space yet can be reached by tuning T(BCP) further to zero. Using high-resolution measurements of the magnetocaloric effect, we demonstrate that the magnetic Grüneisen parameter ΓH indeed both changes sign and diverges as required for quantum criticality. Moreover, ΓH displays a characteristic scaling behavior but only on the low-field side H≲H(BCP), indicating a pronounced asymmetry with respect to the critical field. We speculate that the small value of T(BCP) is related to the geometric frustration of the Kondo lattice of YbAgGe.
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Affiliation(s)
- Y Tokiwa
- I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany
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18
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Abstract
Quantum criticality in the normal and superconducting states of the heavy-fermion metal CeCoIn5 is studied by measurements of the magnetic Grüneisen ratio ΓH and specific heat in different field orientations and temperatures down to 50 mK. A universal temperature over magnetic field scaling of ΓH in the normal state indicates a hidden quantum critical point at zero field. Within the superconducting state, the quasiparticle entropy at constant temperature increases upon reducing the field towards zero, providing additional evidence for zero-field quantum criticality.
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Affiliation(s)
- Y Tokiwa
- I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany
| | - E D Bauer
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - P Gegenwart
- I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany
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19
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Dong JK, Tokiwa Y, Bud'ko SL, Canfield PC, Gegenwart P. Anomalous reduction of the Lorenz ratio at the quantum critical point in YbAgGe. Phys Rev Lett 2013; 110:176402. [PMID: 23679749 DOI: 10.1103/physrevlett.110.176402] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2013] [Indexed: 06/02/2023]
Abstract
We report measurements of the electrical and thermal transport on the hexagonal heavy-fermion metal YbAgGe for temperatures T ≥ 40 mK and in magnetic fields H∥ab up to 14 T. This distorted kagome-lattice system displays a series of magnetic states and a quantum critical point at H(c) = 4.5 T. The Lorenz ratio L(T)/L0 displays a marked reduction only close to H(c). A T-linear contribution below 120 mK, present at all different fields, allows us to extrapolate the Lorenz ratio towards T = 0. At the critical field this yields L/L0 = 0.92±0.03, suggesting a violation of the Wiedemann-Franz law due to strong inelastic scattering.
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Affiliation(s)
- J K Dong
- I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany
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20
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Tokiwa Y, Bauer ED, Gegenwart P. Quasiparticle entropy in the high-field superconducting phase of CeCoIn(5). Phys Rev Lett 2012; 109:116402. [PMID: 23005654 DOI: 10.1103/physrevlett.109.116402] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2012] [Revised: 06/22/2012] [Indexed: 06/01/2023]
Abstract
The heavy-fermion superconductor CeCoIn(5) displays an additional transition within its superconducting (SC) state, whose nature is characterized by high-precision studies of the isothermal field dependence of the entropy, derived from combined specific heat and magnetocaloric effect measurements at temperatures T≥100 mK and fields H≤12 T aligned along different directions. For any of these conditions, we do not observe an additional entropy contribution upon tuning at constant temperature by magnetic field from the homogeneous SC into the presumed Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) SC state. By contrast, for H∥[100] a reduction of entropy was found that quantitatively agrees with the expectation for spin-density-wave order without FFLO superconductivity. Our data exclude the formation of a FFLO state in CeCoIn(5) for out-of-plane field directions, where no spin-density-wave order exists.
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Affiliation(s)
- Y Tokiwa
- I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany
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21
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Tokiwa Y, Gegenwart P. High-resolution alternating-field technique to determine the magnetocaloric effect of metals down to very low temperatures. Rev Sci Instrum 2011; 82:013905. [PMID: 21280843 DOI: 10.1063/1.3529433] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The magnetocaloric effect or "magnetic Grüneisen ratio" Γ(H)=T(-1)(dT/dH)(S) quantifies the cooling or heating of a material when an applied magnetic field is changed under adiabatic conditions. Recently, this property has attracted considerable interest in the field of quantum criticality. Here, we report the development of a low-frequency alternating-field technique for measurements of the magnetocaloric effect down to very low temperatures, which is an important property for the study of quantum critical points. We focus, in particular, on highly conducting metallic samples and discuss the influence of eddy current heating. By comparison with magnetization and specific heat measurements, we demonstrate that our fast and accurate technique gives quantitatively correct values for the magnetocaloric effect under truly adiabatic conditions.
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Affiliation(s)
- Y Tokiwa
- Physik. Institut, Georg-August-Universität Göttingen, Germany.
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22
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Pranamuda H, Tokiwa Y, Tanaka H. Microbial degradation of an aliphatic polyester with a high melting point, poly(tetramethylene succinate). Appl Environ Microbiol 2010; 61:1828-32. [PMID: 16535023 PMCID: PMC1388441 DOI: 10.1128/aem.61.5.1828-1832.1995] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The biodegradability of poly(tetramethylene succinate) (PTMS), a synthetic aliphatic polyester with a high melting point, was evaluated. The ecological study showed that the distribution of PTMS-degrading microorganisms in soil environments was quite restricted compared with the distribution of microorganisms that degrade poly((epsilon)-caprolactone) (PCL), a polyester with a low melting point. However, in soil samples in which the formation of a clear zone was observed, PTMS-degrading microorganisms constituted 0.2 to 6.0% of the total number of microorganisms, which is very close to the percentage (0.8 to 8.0%) observed for PCL-degrading microorganisms. Five strains were isolated from colonies which formed distinct clear zones on agar plates with emulsified PTMS. In liquid cultures of the isolates with ground PTMS powder, strain HT-6, an actinomycete, showed the highest PTMS degrading activity. It assimilated about 60% of the ground PTMS powder after 8 days of cultivation. When a PTMS emulsion was used, a higher degradation rate was observed and more than 90% of the PTMS was assimilated in 6 days. PTMS degradation products were analyzed by gas chromatography, and it was found that 1,4-butanediol, 4-hydroxy n-butyrate, and succinic acid accumulated during cultivation. Degradation of PTMS film by the strain occurred in two steps: fragmentation and then the formation of hemispherical holes on the surface of the film. Strain HT-6 was also able to assimilate PCL and poly((beta)-hydroxybutyrate) (PHB). The crude enzyme showed a wide range of substrate specificity, being able to degrade low-molecular-weight PTMS, PCL, PHB, and even high-molecular-weight PTMS.
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Steglich F, Arndt J, Friedemann S, Krellner C, Tokiwa Y, Westerkamp T, Brando M, Gegenwart P, Geibel C, Wirth S, Stockert O. Superconductivity versus quantum criticality: what can we learn from heavy fermions? J Phys Condens Matter 2010; 22:164202. [PMID: 21386408 DOI: 10.1088/0953-8984/22/16/164202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Two quantum critical point (QCP) scenarios are being discussed for different classes of antiferromagnetic (AF) heavy-fermion (HF) systems. In the itinerant one, where AF order is of the spin-density wave (SDW) type, the heavy 'composite' charge carriers keep their integrity at the QCP. The second one implies a breakdown of the Kondo effect and a disintegration of the composite fermions at the AF QCP. We discuss two isostructural compounds as exemplary materials for these two different scenarios: CeCu(2)Si(2) exhibits a three-dimensional (3D) SDW QCP and superconductivity, presumably mediated by SDW fluctuations, as strongly suggested by recent inelastic neutron scattering experiments. In Y bRh(2)Si(2), the AF QCP is found to coincide with a Kondo-destroying one. However, in the latter compound these two QCPs can be detached by varying the average unit-cell volume, e.g. through the application of chemical pressure, as realized by partial substitution of either Ir or Co for Rh. A comparison of CeCu(2)Si(2) and Y bRh(2)Si(2) indicates that the apparent differences in quantum critical behaviour go along with disparate behaviour concerning the (non-) existence of superconductivity (SC). No sign of SC could be detected in Y bRh(2)Si(2) down to mK temperatures. A potential correlation between the specific nature of the QCP and the occurrence of SC, however, requires detailed studies on further quantum critical HF superconductors, e.g. on β-Y bAlB(4), UBe(13), CeCoIn(5) and CeRhIn(5).
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Affiliation(s)
- F Steglich
- Max Planck Institut für Chemische Physik fester Stoffe, Nöthnitzer Strasse 40, D-01187 Dresden, Germany.
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Kurita N, Ronning F, Tokiwa Y, Bauer ED, Subedi A, Singh DJ, Thompson JD, Movshovich R. Low-temperature magnetothermal transport investigation of a Ni-based superconductor BaNi2As2: evidence for fully gapped superconductivity. Phys Rev Lett 2009; 102:147004. [PMID: 19392475 DOI: 10.1103/physrevlett.102.147004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2008] [Indexed: 05/27/2023]
Abstract
We have performed low-temperature specific heat and thermal conductivity measurements of the Ni-based superconductor BaNi2As2 (T{c}=0.7 K) in a magnetic field. In a zero field, thermal conductivity shows T-linear behavior in the normal state and exhibits a BCS-like exponential decrease below T{c}. The field dependence of the residual thermal conductivity extrapolated to zero temperature is indicative of a fully gapped superconductor. This conclusion is supported by the analysis of the specific heat data, which are well fit by the BCS temperature dependence from T{c} down to the lowest temperature of 0.1 K.
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Affiliation(s)
- N Kurita
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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25
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Tokiwa Y, Radu T, Geibel C, Steglich F, Gegenwart P. Divergence of the magnetic Grüneisen ratio at the field-induced quantum critical point in YbRh2Si2. Phys Rev Lett 2009; 102:066401. [PMID: 19257612 DOI: 10.1103/physrevlett.102.066401] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/22/2008] [Indexed: 05/27/2023]
Abstract
The heavy-fermion metal YbRh2Si2 is studied by low-temperature magnetization M(T) and specific-heat C(T) measurements at magnetic fields close to the quantum critical point (H_{c}=0.06 T, H perpendicularc). Upon approaching the instability, dM/dT is more singular than C(T), leading to a divergence of the magnetic Grüneisen ratio Gamma_{mag}=-(dM/dT)/C. Within the Fermi-liquid regime, Gamma_{mag}=-G_{r}(H-H_{c};{fit}) with G_{r}=-0.30+/-0.01 and H_{c};{fit}=(0.065+/-0.005) T which is consistent with scaling behavior of the specific-heat coefficient in YbRh2(Si0.95Ge0.05)_{2}. The field dependence of dM/dT indicates an inflection point of the entropy as a function of magnetic field upon passing the line T;{ small star, filled}(H) previously observed in Hall and thermodynamic measurements.
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Affiliation(s)
- Y Tokiwa
- Max-Planck Institute for Chemical Physics of Solids, D-01187 Dresden, Germany
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Park T, Sidorov VA, Ronning F, Zhu JX, Tokiwa Y, Lee H, Bauer ED, Movshovich R, Sarrao JL, Thompson JD. Isotropic quantum scattering and unconventional superconductivity. Nature 2008; 456:366-8. [PMID: 19020616 DOI: 10.1038/nature07431] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2008] [Accepted: 09/10/2008] [Indexed: 11/09/2022]
Abstract
Superconductivity without phonons has been proposed for strongly correlated electron materials that are tuned close to a zero-temperature magnetic instability of itinerant charge carriers. Near this boundary, quantum fluctuations of magnetic degrees of freedom assume the role of phonons in conventional superconductors, creating an attractive interaction that 'glues' electrons into superconducting pairs. Here we show that superconductivity can arise from a very different spectrum of fluctuations associated with a local (or Kondo-breakdown) quantum critical point that is revealed in isotropic scattering of charge carriers and a sublinear, temperature-dependent electrical resistivity. At this critical point, accessed by applying pressure to the strongly correlated, local-moment antiferromagnet CeRhIn(5), magnetic and charge fluctuations coexist and produce electronic scattering that is maximal at the optimal pressure for superconductivity. This previously unanticipated source of pairing glue opens possibilities for understanding and discovering new unconventional forms of superconductivity.
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Affiliation(s)
- T Park
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
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27
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Tokiwa Y, Movshovich R, Ronning F, Bauer ED, Papin P, Bianchi AD, Rauscher JF, Kauzlarich SM, Fisk Z. Anisotropic effect of Cd and Hg doping on the Pauli limited superconductor CeCoIn5. Phys Rev Lett 2008; 101:037001. [PMID: 18764281 DOI: 10.1103/physrevlett.101.037001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2008] [Indexed: 05/26/2023]
Abstract
We studied the effect of impurity on the first order superconducting (SC) transition and the high field-low temperature (HFLT) SC state of CeCoIn5 by measuring the specific heat of CeCo(In1-xCdx)_{5} with x=0.0011, 0.0022, and 0.0033 and CeCo(In1-xHgx)_{5} with x=0.000 16, 0.000 32, and 0.000 48 at temperatures down to 0.1 K and fields up to 14 T. Cd substitution rapidly suppresses the crossover temperature T0, where the SC transition changes from second to first order, to T=0 K with x=0.0022 for H parallel[100], while it remains roughly constant up to x=0.0033 for H parallel[001]. The associated anomaly of the proposed FFLO state in Hg-doped samples is washed out by x=0.000 48, while remaining at the same temperature, indicating high sensitivity of that state to impurities. We interpret these results as supporting the nonmagnetic, possibly FFLO, origin of the HFLT state in CeCoIn5.
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Affiliation(s)
- Y Tokiwa
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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Ugwu C, Tokiwa Y, Aoyagi H, Uchiyama H, Tanaka H. UV mutagenesis ofCupriavidus necatorfor extracellular production of (R)-3-hydroxybutyric acid. J Appl Microbiol 2008; 105:236-42. [DOI: 10.1111/j.1365-2672.2008.03774.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Gegenwart P, Westerkamp T, Krellner C, Tokiwa Y, Paschen S, Geibel C, Steglich F, Abrahams E, Si Q. Multiple Energy Scales at a Quantum Critical Point. Science 2007; 315:969-71. [PMID: 17303749 DOI: 10.1126/science.1136020] [Citation(s) in RCA: 191] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
We report thermodynamic measurements in a magnetic-field-driven quantum critical point of a heavy fermion metal, YbRh2Si2. The data provide evidence for an energy scale in the equilibrium excitation spectrum that is in addition to the one expected from the slow fluctuations of the order parameter. Both energy scales approach zero as the quantum critical point is reached, thereby providing evidence for a new class of quantum criticality.
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Affiliation(s)
- P Gegenwart
- Max Planck Institute for Chemical Physics of Solids, D-01187 Dresden, Germany.
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Tokiwa Y, Kitagawa M, Raku T. Enzymatic synthesis of arbutin undecylenic acid ester and its inhibitory effect on mushroom tyrosinase. Biotechnol Lett 2006; 29:481-6. [PMID: 17195058 DOI: 10.1007/s10529-006-9267-4] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2006] [Revised: 11/08/2006] [Accepted: 11/22/2006] [Indexed: 11/30/2022]
Abstract
A novel tyrosinase inhibitor, an arbutin derivative having undecylenic acid at the 6-position of its glucose moiety, was enzymatically synthesized. Its inhibitory activity was studied in vitro by using catechol and phenol as substrates. The IC(50) value of the arbutin ester on tyrosinase using catechol (4 x 10(-4) M) was 1% of that when arbutin (4 x 10(-2) M) was used. Using phenol, IC(50) of the arbutin ester (3 x 10(-4) M) as substrate was 10% of that of arbutin (3 x 10(-3) M). These results suggest that the arbutin ester inhibits the latter part of the tyrosinase reaction, which consists of hydroxylation and oxidation.
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Affiliation(s)
- Y Tokiwa
- National Institute of Advanced Industrial Science and Technology, Central 6, 1-1-1 Higashi, Tsukuba, Ibaraki, Japan.
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Tokiwa Y, Gegenwart P, Radu T, Ferstl J, Sparn G, Geibel C, Steglich F. Field-induced suppression of the heavy-fermion state in YbRh2Si2. Phys Rev Lett 2005; 94:226402. [PMID: 16090416 DOI: 10.1103/physrevlett.94.226402] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2004] [Indexed: 05/03/2023]
Abstract
We report dc-magnetization measurements on YbRh2Si2 at temperatures down to 0.04 K, magnetic fields B< or =11.5 T, and under hydrostatic pressure P< or =1.3 GPa. At ambient pressure a kink at B* =9.9 T indicates a new type of field-induced transition from an itinerant to a localized 4f state. This transition is different from the metamagnetic transition observed in other heavy-fermion compounds, as here ferromagnetic rather than antiferromagnetic correlations dominate below B*. Hydrostatic pressure experiments reveal a clear correspondence of B* to the characteristic spin fluctuation temperature determined from specific heat.
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Affiliation(s)
- Y Tokiwa
- Max-Planck-Institute for Chemical Physics of Solids, D-01187 Dresden, Germany
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Gegenwart P, Custers J, Tokiwa Y, Geibel C, Steglich F. Ferromagnetic quantum critical fluctuations in YbRh2(Si0.95Ge0.05)2. Phys Rev Lett 2005; 94:076402. [PMID: 15783833 DOI: 10.1103/physrevlett.94.076402] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2004] [Indexed: 05/24/2023]
Abstract
The bulk magnetic susceptibility chi(T,B) of YbRh(2)(Si(0.95)Ge(0.05))(2) has been investigated close to the field-induced quantum critical point at B(c) = 0.027 T. For B < or= 0.05 T a Curie-Weiss law with a negative Weiss temperature is observed at temperatures below 0.3 K. Outside this region, the susceptibility indicates ferromagnetic quantum critical fluctuations, chi(T) proportional, variantT-0.6 above 0.3 K. At low temperatures the Pauli susceptibility follows chi(0) proportional, variant(B-B(c))(-0.6) and scales with the coefficient of the T(2) term in the electrical resistivity. The Sommerfeld-Wilson ratio is highly enhanced and increases up to 30 close to the critical field.
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Affiliation(s)
- P Gegenwart
- Max-Planck Institute for Chemical Physics of Solids, D-01187 Dresden, Germany
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Custers J, Gegenwart P, Wilhelm H, Neumaier K, Tokiwa Y, Trovarelli O, Geibel C, Steglich F, Pépin C, Coleman P. The break-up of heavy electrons at a quantum critical point. Nature 2003; 424:524-7. [PMID: 12891349 DOI: 10.1038/nature01774] [Citation(s) in RCA: 160] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2003] [Accepted: 05/28/2003] [Indexed: 11/09/2022]
Abstract
The point at absolute zero where matter becomes unstable to new forms of order is called a quantum critical point (QCP). The quantum fluctuations between order and disorder that develop at this point induce profound transformations in the finite temperature electronic properties of the material. Magnetic fields are ideal for tuning a material as close as possible to a QCP, where the most intense effects of criticality can be studied. A previous study on the heavy-electron material YbRh2Si2 found that near a field-induced QCP electrons move ever more slowly and scatter off one another with ever increasing probability, as indicated by a divergence to infinity of the electron effective mass and scattering cross-section. But these studies could not shed light on whether these properties were an artefact of the applied field, or a more general feature of field-free QCPs. Here we report that, when germanium-doped YbRh2Si2 is tuned away from a chemically induced QCP by magnetic fields, there is a universal behaviour in the temperature dependence of the specific heat and resistivity: the characteristic kinetic energy of electrons is directly proportional to the strength of the applied field. We infer that all ballistic motion of electrons vanishes at a QCP, forming a new class of conductor in which individual electrons decay into collective current-carrying motions of the electron fluid.
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Affiliation(s)
- J Custers
- Max-Planck-Institute for Chemical Physics of Solids, D-01187 Dresden, Germany
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Abstract
To improve trehalose lipophilicity, trehalose was regioselectively esterified with vinyl fatty acid esters in dimethyl formamide by protease from Bacillus subtilis to give 6-O-lauroyltrehalose, 6-O-myristoyltrehalose, 6-O-palmitoyltrehalose, 6-O-stearoyltrehalose, 6-O-oleoyltrehalose and 6-O-linoleoyltrehalose. The influence of structural variation by changing fatty acid substitute was examined by measurement of the surface tension and biodegradability.
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Affiliation(s)
- T Raku
- New Energy and Industrial Technology Development Organization (NEDO), Tsukuba Central 6, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8566, Japan
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Abstract
While hemoglobin is one of the most well characterized proteins due to its function in oxygen transport, few additional properties of hemoglobin have been described. While screening serum samples for novel antimicrobial factors, it was found that intact hemoglobin tetramers, including that from human, exhibited considerable activity against gram-positive and gram-negative bacteria, and fungi. To further characterize this surprising activity, the antimicrobial potency of sections of human hemoglobin was tested against a panel of microorganisms. In all cases separate testing of the alpha and beta subunits provided activity at least as potent as the intact tetramer. This activity is derived from the protein portion of hemoglobin since removal of the heme prosthetic group did not lead to decreases in potency. In addition, cyanogen bromide cleavage of both subunits provided fragments that still contained substantial antimicrobial activity. It has been possible to map specific regions of the human hemoglobin molecule that are responsible for significant antimicrobial activity. The carboxyl terminal thirty amino acids of the beta subunit, which form a cationic alpha-helix based on the crystal structure of the intact tetramer, were active against Escherichia coli, Staphylococcus aureus and Candida albicans. In view of the fact that different hemoglobin-derived peptide fragments exhibit diverse antibiotic activities, it is conceivable that, in addition to its role in oxygen transport. hemoglobin functions as an important multi-defense agent against a wide range of microorganisms.
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Affiliation(s)
- C A Parish
- Department of Chemistry, Columbia University, New York, NY 10027, USA
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Uchida H, Nakajima-Kambe T, Shigeno-Akutsu Y, Nomura N, Tokiwa Y, Nakahara T. Properties of a bacterium which degrades solid poly(tetramethylene succinate)-co-adipate, a biodegradable plastic. FEMS Microbiol Lett 2000; 189:25-9. [PMID: 10913861 DOI: 10.1111/j.1574-6968.2000.tb09201.x] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Various microorganisms were screened for their ability to degrade poly(tetramethylene succinate)-co-(tetramethylene adipate) (PBSA). Strain BS-3, which was newly isolated from a soil sample, was selected as the best strain. From taxonomical studies, the strain was tentatively ascribed to belong to the genus Acidovorax, most probably to the species A. delafieldii. Strain BS-3 could degrade both solid and emulsified PBSA, and also emulsified poly(tetramethylene succinate). During the degradation, a lipase activity was observed in the culture broth. This lipase activity was induced more strongly by PBSA than by tributyrin or triolein which are typical substrates of lipase. These observations strongly suggest that this lipase was involved in the PBSA biodegradation in strain BS-3.
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Affiliation(s)
- H Uchida
- Institute of Applied Biochemistry, University of Tsukuba, Japan
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Maszenan AM, Seviour RJ, Patel BK, Schumann P, Burghardt J, Tokiwa Y, Stratton HM. Three isolates of novel polyphosphate-accumulating gram-positive cocci, obtained from activated sludge, belong to a new genus, Tetrasphaera gen. nov., and description of two new species, Tetrasphaera japonica sp. nov. and Tetrasphaera australiensis sp. nov. Int J Syst Evol Microbiol 2000; 50 Pt 2:593-603. [PMID: 10758865 DOI: 10.1099/00207713-50-2-593] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Two isolates of Gram-positive cocci (Ben 109T and Ben 110) which could accumulate polyphosphate and were microscopically similar in appearance to so-called 'G-bacteria', appearing as tetrads, were isolated from samples of activated sludge biomass by micromanipulation and grown in axenic culture. On the basis of their phenotypic and chemotaxonomic characters and 16S rDNA sequences, these isolates, together with strain T1-X7T isolated and described previously in Japan, belong to a new genus. These isolates are phylogenetically different from Tessaracoccus bendigoensis, Friedmanniella spumicola and Friedmanniella capsulata, Gram-positive cocci isolated previously in this laboratory. They are characterized by type A1 gamma peptidoglycan, with meso-diaminopimelic acid as the diagnostic diamino acid. The main cellular fatty acid of Ben 109T, Ben 110 and T1-X7T is 14-methylpentadecanoic acid (i-C16:0). The major menaquinones of Ben 109T are MK-8(H4), with MK-8(H2) and MK-8 in trace amounts. In Ben 110 MK-8(H4) and MK-6(H4) are the major menaquinones, while T1-X7T has MK-8(H4), MK-7(H4) and MK-6(H4) as its menaquinones. All three contain phosphatidylinositol, phosphatidylglycerol and diphosphatidylglycerol as their polar lipids. These properties, together with 16S rDNA sequence data, suggest that they all belong to a single new genus for which the name Tetrasphaera gen. nov. is proposed. However, the lipid, cellular fatty acid profiles and DNA-DNA similarity data suggest that Ben 109T and Ben 110 are sufficiently different from T1-X7T to represent a different species of the genus Tetrasphaera. Strain T1-X7T represents the type species Tetrasphaera japonica sp. nov. of this new genus, and strains Ben 109T and Ben 110 belong to the other species, Tetrasphaera australiensis sp. nov.
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Abstract
Amycolatopsis sp. strain HT-6, a poly(tetramethylene succinate) (PTMS)-degrading actinomycete, was observed to degrade poly(tetramethylene carbonate) (PTMC). In a liquid culture with 150 mg of PTMC film, 59% degradation was achieved, but with a low yield of cell growth. On the other hand, PTMS copolymerized with a small amount of PTMC, forming a copolyester carbonate (PEC) that was completely and rapidly degraded with a high yield of cell growth.
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Affiliation(s)
- H Pranamuda
- Agency for the Assessment and Application of Technology, Jakarta 10340, Indonesia
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Ohkuni H, Inada Y, Tokiwa Y, Sakurai K, Settai R, Honma T, Haga Y, Yamamoto E, Yamagami H, Takahashi S, Yanagisawa T. Fermi surface properties and de Haas-van Alphen oscillation in both the normal and superconducting mixed states of URu2Si2. ACTA ACUST UNITED AC 1999. [DOI: 10.1080/014186399256916] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
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Asada Y, Miyake M, Miyake J, Kurane R, Tokiwa Y. Photosynthetic accumulation of poly-(hydroxybutyrate) by cyanobacteria--the metabolism and potential for CO2 recycling. Int J Biol Macromol 1999; 25:37-42. [PMID: 10416648 DOI: 10.1016/s0141-8130(99)00013-6] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Regulatory mechanism in PHB [poly-(hydroxybutyrate)] accumulation by cyanobacteria, especially by a thermophilic isolate, Synechococcus MA19 was reviewed in comparison with a genetically engineered strain. The strain, MA19 accumulates PHB under nitrogen starved and photoautotrophic conditions (MA19-N). Little PHB synthase activity was detected in crude extracts from the cells grown in nitrogen sufficient conditions (MA19 + N). The activity was detected exclusively in membrane fractions from MA19 + N. The change of the enzyme activity was insensitive to chloramphenicol, which suggests post-translational activation. In vitro, acetyl phosphate activated PHB synthase in membrane fractions from MA19 + N, and the extent of activation depended on the concentration of acetyl phosphate. Phosphotransacetylase which catalyzes the conversion of acetyl-CoA to acetyl phosphate was detected in crude extracts from MA19-N but not in those from MA19 + N. These results suggested that intracellular acetyl phosphate concentration could be controlled, depending on C-N balance and intracellular acetyl-CoA concentration. On the contrary, in genetically-engineered cyanobacterium (transformant with PHB synthesizing genes from Ralstonia eutropha), it did not seem to be PHB synthase but acetyl-CoA flux that limits PHB synthesis. The closer association of PHB granules with thylakoid membranes in MA19 is suggested than that in the genetically-engineered cyanobacterium, which may reflect the difference of distribution of PHB synthase. Transposon-mutagenesis was used to acquire mutants of its altered PHB regulatory mechanism. PHA production by cyanobacteria was considered from the aspects of photobioreactors.
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Affiliation(s)
- Y Asada
- National Institute of Bioscience and Human-Technology, Tsukuba, Ibaraki, Japan.
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Suyama T, Shigematsu T, Takaichi S, Nodasaka Y, Fujikawa S, Hosoya H, Tokiwa Y, Kanagawa T, Hanada S. Roseateles depolymerans gen. nov., sp. nov., a new bacteriochlorophyll a-containing obligate aerobe belonging to the beta-subclass of the Proteobacteria. Int J Syst Bacteriol 1999; 49 Pt 2:449-57. [PMID: 10319464 DOI: 10.1099/00207713-49-2-449] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Strains 61AT (T = type strain) and 61B2, the first bacteriochlorophyll (BChl) a-containing obligate aerobes to be classified in the beta-subclass of the Proteobacteria, were isolated from river water. The strains were originally isolated as degraders of poly(hexamethylene carbonate) (PHC). The organisms can utilize PHC and some other biodegradable plastics. The strains grow only under aerobic conditions. Good production of BChl a and caroterioid pigments is achieved on PHC agar plates and an equivalent production is observed under oligotrophic conditions on agar medium. Spectrometric results suggest that BChl a is present in light-harvesting complex I and the photochemical reaction centre. The main carotenoids are spirilloxanthin and its precursors. Analysis of the 16S rRNA gene sequence indicated that the phylogenetic positions of the two strains are similar to each other and that their closest relatives are the genera Rubrivivax, ideonella and Leptothrix with similarities of 96.3, 96.2 and 96.1%, respectively. The cells are motile, straight rods and contain poly-beta-hydroxybutyrate granules. Ubiquinone-8 is the predominant quinone. Vitamins are not required for growth. The G + C content of genomic DNA is 66.2-66.3 mol%. Genetic and phenotypic features suggest that the strains represent a new genus in the beta-subclass which is evenly distant from known genera. Consequently, the name Roseateles depolymerans gen. nov., sp. nov. is proposed for the strains; the type strain of Roseateles depolymerans is strain 61AT (= DSM 11813T).
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Affiliation(s)
- T Suyama
- National Institute of Bioscience and Human Technology, Ibaraki, Japan.
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42
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Tsuchii A, Tokiwa Y. Colonization and disintegration of tire rubber by a colonial mutant of nocardia. J Biosci Bioeng 1999; 87:542-4. [PMID: 16232513 DOI: 10.1016/s1389-1723(99)80108-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/1998] [Accepted: 01/23/1999] [Indexed: 11/25/2022]
Abstract
Forty-seven percent of a tire tread strip with a natural rubber content of 100 phr (parts per hundred of rubber) was completely mineralized by a mutant strain, Rc, of the rubber-degrading organism, Nocardia sp. strain 835A, while 34% was disintegrated into very small particles after a cultivation period of 8 weeks.
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Affiliation(s)
- A Tsuchii
- Applied Microbiology Department, National Institute of Bioscience and Human-Technology, Higashi, Tsukuba, Ibaragi 305-0046, Japan
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Suyama T, Tokiwa Y, Ouichanpagdee P, Kanagawa T, Kamagata Y. Phylogenetic affiliation of soil bacteria that degrade aliphatic polyesters available commercially as biodegradable plastics. Appl Environ Microbiol 1998; 64:5008-11. [PMID: 9835597 PMCID: PMC90957 DOI: 10.1128/aem.64.12.5008-5011.1998] [Citation(s) in RCA: 111] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Thirty-nine morphologically different soil bacteria capable of degrading poly(beta-hydroxyalkanoate), poly(epsilon-caprolactone), poly(hexamethylene carbonate), or poly(tetramethylene succinate) were isolated. Their phylogenetic positions were determined by 16S ribosomal DNA sequencing, and all of them fell into the classes Firmicutes and Proteobacteria. Determinations of substrate utilization revealed characteristic patterns of substrate specificities.
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Affiliation(s)
- T Suyama
- National Institute of Bioscience and Human Technology, Agency of Industrial Science and Technology, Tsukuba, Ibaraki 305-8566, Japan.
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Abstract
Bacteria that degrade an aliphatic polycarbonate, poly(hexamethylene carbonate), were isolated from river water in Ibaraki. Prefecture, Japan, after enrichment in liquid medium containing poly(hexamethylene carbonate) suspensions as carbon source, and dilution to single cells. Four of the strains, 35L, WFF52, 61A and 61B2, degraded poly(hexamethylene carbonate) on agar plate containing suspended poly(hexamethylene carbonate). Degradation of poly(hexamethylene carbonate) was confirmed by gel permeation chromatography. Besides poly(hexamethylene carbonate), the strains were found to degrade poly(tetramethylene carbonate). The strains were characterized morphologically, physiologically, and by 16S rDNA sequence analysis. Strains 35L and WFF52 were tentatively identified as Pseudomonas sp. and Variovorax sp., respectively, while strains 61A and 61B2 constitute an unidentified branch within the beta subclass of the Proteobacteria.
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Affiliation(s)
- T Suyama
- National Institute of Bioscience and Human Technology, Tsukuba, Ibaraki, Japan.
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45
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Abstract
Of 10 strains of mannanase-producing anaerobic bacteria isolated from soils and methanogenic sludges, Clostridium tertium KT-5A, which was isolated from lotus soil, produced high amounts of extracellular beta-1,4-mannanase. The isolate was an aerotolerant anaerobe without quinon systems; the cell growth cultivated with no addition of reducing agents was also stable. High yields of mannanase were obtained by inducing enzyme production with galactomannan guar gum and beef extract/peptone as carbon and nitrogen sources, respectively. Fermentation end products on galactomannan fermentation were formate, acetate, lactate, butyrate, carbon dioxide and hydrogen. The extracellular mannanase displayed high activity on galactomannans of locust bean gum galactose/mannose (G/M) ratio 1:4 and spino gum (G/M 1:3), but weak activity on guar gum galactomannan (G/M 1:2) and konjac glucomannan. As far as is known, this is the first report on the isolation of an active mannanase-producing anaerobic bacterium from natural environments.
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Affiliation(s)
- N Kataoka
- Research and Development Department, Ebara Corporation, Kanagawa, Japan
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46
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Abstract
By applying the plate count and clear-zone methods, it was confirmed that polylactide (PLA)-degrading microorganisms are sparsely distributed in soil environments. An Amycolatopsis isolate was successfully isolated. Microbial degradation of PLA film was demonstrated; i.e., about 60% of the 100-mg film initially added was degraded by the strain after 14 days of liquid culture.
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Abstract
A strip of tread compound cut from a truck tire was degraded only slightly when it was used as the sole growth substrate for a strain of Nocardia. On the contrary, its degradation was markedly enhanced by addition of a strip cut from a latex glove which the organism readily utilized as a growth substrate. When a glove strip was added, the biomass concentration in the experimental flask became more than 10-fold higher than the control without a glove strip and the colonization of the tire strip was significantly enhanced. After 8 weeks' cultivation, about 28% of the tire strip was disintegrated into very small black particles (mostly less than 30 microns in diameter) and the weight of the remaining unchanged portion of the strip was about 49% of the initial weight. Four kinds of truck tire treads were attacked in differing degrees by the organism under the same conditions. The treads containing more than 70 phr (parts per hundred of rubber) of natural rubber were considerably attacked, while those with a natural rubber content of less than 55 phr were attacked only slightly. The microbial activity against the rubber in the side wall of a truck tire was relatively high, but the inner liner was hardly attacked and the bead rubber not at all.
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Affiliation(s)
- A Tsuchii
- Applied Microbiology Department, National Institute of Bioscience and Human-Technology, Ibaragi, Japan
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Palevsky PM, Burr R, Moreland L, Tokiwa Y, Greenberg A. Failure of low molecular weight dextran to prevent clotting during continuous renal replacement therapy. ASAIO J 1995; 41:847-9. [PMID: 8589465] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Clotting of the extracorporeal circuit during continuous renal replacement therapy results in decreased ultrafiltration rates, impaired solute clearance and, ultimately, occlusion of the extracorporeal circuit. The authors conducted an open-label randomized controlled trial to determine whether low molecular weight dextran could prevent hemofilter clotting in patients undergoing continuous venovenous hemodialysis. Eleven patients were randomized to receive a continuous infusion of 10% low molecular weight dextran at 25 mL/hr; 8 patients served as control subjects. No differences in the frequency of hemofilter clotting or hemofilter lifespan were detected. The authors concluded that continuous infusion of low dose low molecular weight dextran is not effective in preventing clotting during continuous renal replacement therapy.
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Affiliation(s)
- P M Palevsky
- Department of Medicine, University of Pittsburgh School of Medicine, Pennsylvania 15261, USA
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Takagi S, Koyama M, Kameyama H, Tokiwa Y. Development of Polycaprolactone/Gelatinized Starch Blends and Their Enzymatic Degradation. Studies in Polymer Science 1994. [DOI: 10.1016/b978-0-444-81708-2.50048-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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