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Korshunov MM, Kuzmichev SA, Kuzmicheva TE. Direct Observation of the Spin Exciton in Andreev Spectroscopy of Iron-Based Superconductors. MATERIALS (BASEL, SWITZERLAND) 2022; 15:6120. [PMID: 36079499 PMCID: PMC9458014 DOI: 10.3390/ma15176120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/29/2022] [Revised: 08/31/2022] [Accepted: 09/01/2022] [Indexed: 06/15/2023]
Abstract
Quasiparticle excitations provide viable information on the physics of unconventional superconductors. Higgs and Leggett modes are some of the classic examples. Another important bosonic excitation is the spin exciton originating from the sign-changing superconducting gap structure. Here we report a direct observation of the temperature-dependent spin exciton in the Andreev spectra of iron-based superconductors. Combined with the other experimental evidence, our observation confirms the extended s-wave (s±) order parameter symmetry and indirectly proves the spin-fluctuation mechanism of Cooper pairing.
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Affiliation(s)
- Maxim M. Korshunov
- Kirensky Institute of Physics, Federal Research Center KSC SB RAS, Akademgorodok, 660036 Krasnoyarsk, Russia
| | - Svetoslav A. Kuzmichev
- Faculty of Physics, Lomonosov Moscow State University, 119991 Moscow, Russia
- Lebedev Physical Institute, Russian Academy of Sciences, 119991 Moscow, Russia
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2
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Zhao L, Liu H, Tong S, Wang J, Han T, Liu C, Gao C, Han Y. Application of impedance spectroscopy in exploring electrical properties of dielectric materials under high pressure. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2022; 34:434001. [PMID: 35973420 DOI: 10.1088/1361-648x/ac8a33] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/21/2022] [Accepted: 08/16/2022] [Indexed: 06/15/2023]
Abstract
Impedance spectroscopy (IS) is an indispensable method of exploring electrical properties of materials. In this review, we provide an overview on the specific applications of IS measurement in the investigations of various electrical properties of materials under high pressure, including electric conduction in bulk and grain boundary, dielectric properties, ionic conduction, and electrostrictive effect. Related studies are summarized to demonstrate the method of analyzing different electrical transport processes with various designed equivalent circuits of IS and reveal some interesting phenomena of electrical properties of materials under high pressure.
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Affiliation(s)
- Lin Zhao
- State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, People's Republic of China
| | - Hao Liu
- State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, People's Republic of China
| | - Shuang Tong
- State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, People's Republic of China
| | - Jia Wang
- Institute for Interdisciplinary Biomass Functional Materials Studies, Jilin Engineering Normal University, Changchun 130052, People's Republic of China
| | - Tao Han
- State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, People's Republic of China
| | - Cailong Liu
- Shandong Key Laboratory of Optical Communication Science and Technology, School of Physical Science and Information Technology of Liaocheng University, Liaocheng 252059, People's Republic of China
| | - Chunxiao Gao
- State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, People's Republic of China
| | - Yonghao Han
- State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, People's Republic of China
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3
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John Mukkattukavil D, Hellsvik J, Ghosh A, Chatzigeorgiou E, Nocerino E, Wang Q, von Arx K, Huang SW, Ekholm V, Hossain Z, Thamizhavel A, Chang J, Månsson M, Nordström L, Såthe C, Agåker M, Rubensson JE, Sassa Y. Resonant inelastic soft x-ray scattering on LaPt 2Si 2. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2022; 34:324003. [PMID: 35640576 DOI: 10.1088/1361-648x/ac7500] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Accepted: 05/31/2022] [Indexed: 06/15/2023]
Abstract
X-ray absorption and resonant inelastic x-ray scattering spectra of LaPt2Si2single crystal at the Si 2pand La 4dedges are presented. The data are interpreted in terms of density functional theory, showing that the Si spectra can be described in terms of Sisanddlocal partial density of states (LPDOS), and the La spectra are due to quasi-atomic local 4fexcitations. Calculations show that Ptd-LPDOS dominates the occupied states, and a sharp localized Lafstate is found in the unoccupied states, in line with the observations.
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Affiliation(s)
| | - Johan Hellsvik
- PDC Center for High Performance Computing, KTH Royal Institute of Technology, SE-106 91 Stockholm, Sweden
- Nordita, KTH Royal Institute of Technology and Stockholm University, Hannes Alfvéns väg 12, SE-106 91 Stockholm, Sweden
| | - Anirudha Ghosh
- MAX IV Laboratory, Lund University, SE-221 00 Lund, Sweden
| | | | - Elisabetta Nocerino
- Department of Applied Physics, KTH Royal Institute of Technology, SE-106 91 Stockholm, Sweden
| | - Qisi Wang
- Physik-Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
| | - Karin von Arx
- Physik-Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
- Department of Physics, Chalmers University of Technology, Göteborg, SE-412 96, Sweden
| | - Shih-Wen Huang
- MAX IV Laboratory, Lund University, SE-221 00 Lund, Sweden
| | - Victor Ekholm
- MAX IV Laboratory, Lund University, SE-221 00 Lund, Sweden
| | - Zakir Hossain
- Department of Physics, Indian Institute of Technology, Kanpur 208016, India
| | | | - Johan Chang
- Physik-Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
| | - Martin Månsson
- Department of Applied Physics, KTH Royal Institute of Technology, SE-106 91 Stockholm, Sweden
| | - Lars Nordström
- Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden
| | - Conny Såthe
- MAX IV Laboratory, Lund University, SE-221 00 Lund, Sweden
| | - Marcus Agåker
- Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden
- MAX IV Laboratory, Lund University, SE-221 00 Lund, Sweden
| | - Jan-Erik Rubensson
- Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden
| | - Yasmine Sassa
- Department of Physics, Chalmers University of Technology, Göteborg, SE-412 96, Sweden
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4
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Band Structure of Organic-Ion-Intercalated (EMIM) xFeSe Superconductor. MATERIALS 2022; 15:ma15051856. [PMID: 35269087 PMCID: PMC8911679 DOI: 10.3390/ma15051856] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/22/2021] [Revised: 02/17/2022] [Accepted: 02/25/2022] [Indexed: 12/10/2022]
Abstract
The band structure and the Fermi surface of the recently discovered superconductor (EMIM)xFeSe are studied within the density functional theory in the generalized gradient approximation. We show that the bands near the Fermi level are formed primarily by Fe-d orbitals. Although there is no direct contribution of EMIM orbitals to the near-Fermi level states, the presence of organic cations leads to a shift of the chemical potential. It results in the appearance of small electron pockets in the quasi-two-dimensional Fermi surface of (EMIM)xFeSe.
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5
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Iron pnictides and chalcogenides: a new paradigm for superconductivity. Nature 2022; 601:35-44. [PMID: 34987212 DOI: 10.1038/s41586-021-04073-2] [Citation(s) in RCA: 30] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Accepted: 09/29/2021] [Indexed: 11/09/2022]
Abstract
Superconductivity is a remarkably widespread phenomenon that is observed in most metals cooled to very low temperatures. The ubiquity of such conventional superconductors, and the wide range of associated critical temperatures, is readily understood in terms of the well-known Bardeen-Cooper-Schrieffer theory. Occasionally, however, unconventional superconductors are found, such as the iron-based materials, which extend and defy this understanding in unexpected ways. In the case of the iron-based superconductors, this includes the different ways in which the presence of multiple atomic orbitals can manifest in unconventional superconductivity, giving rise to a rich landscape of gap structures that share the same dominant pairing mechanism. In addition, these materials have also led to insights into the unusual metallic state governed by the Hund's interaction, the control and mechanisms of electronic nematicity, the impact of magnetic fluctuations and quantum criticality, and the importance of topology in correlated states. Over the fourteen years since their discovery, iron-based superconductors have proven to be a testing ground for the development of novel experimental tools and theoretical approaches, both of which have extensively influenced the wider field of quantum materials.
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6
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Kim MG, Ratcliff W, Pajerowski DM, Kim JW, Yan JQ, Lynn JW, Goldman AI, Kreyssig A. Magnetic ordering and structural distortion in a PrFeAsO single crystal studied by neutron and x-ray scattering. PHYSICAL REVIEW. B 2021; 103:10.1103/physrevb.103.174405. [PMID: 37588030 PMCID: PMC10428661 DOI: 10.1103/physrevb.103.174405] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/18/2023]
Abstract
We report the magnetic ordering and structural distortion in PrFeAsO crystals, the basis compound for one of the oxypnictide superconductors, using high-resolution x-ray diffraction, neutron diffraction, and x-ray resonant magnetic scattering (XRMS). We find the structural tetragonal-to-orthorhombic phase transition at T S = 147 K , the AFM phase transition of the Fe moments at T Fe = 72 K , and the Pr AFM phase transition at T Pr = 21 K . Combined high-resolution neutron diffraction and XRMS show unambiguously that the Pr moments point parallel to the longer orthorhombic a axis and order antiferromagnetically along the a axis but ferromagnetically along the b and c directions in the stripelike AFM order. The temperature-dependent magnetic order parameter of the Pr moments shows no evidence for a reorientation of moments.
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Affiliation(s)
- M. G. Kim
- Department of Physics, University of Wisconsin at Milwaukee, Milwaukee, Wisconsin 53201, USA
- Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA
- Ames Laboratory, US DOE, and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | - W. Ratcliff
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - D. M. Pajerowski
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - J.-W. Kim
- Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA
| | - J.-Q. Yan
- Ames Laboratory, US DOE, and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | - J. W. Lynn
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - A. I. Goldman
- Ames Laboratory, US DOE, and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | - A. Kreyssig
- Ames Laboratory, US DOE, and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
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7
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Sanna S, Carretta P, Moroni M, Prando G, Bonfà P, Allodi G, De Renzi R, Martinelli A. Fast recovery of the pristine magnetic and structural phases in superconducting LaFeAsO 0.89F 0.11 by Mn/Fe substitution. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:174002. [PMID: 30690437 DOI: 10.1088/1361-648x/ab0234] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We report an experimental study on the effect of Mn impurities in the optimally doped [Formula: see text] compound. The results show that a very tiny amount of Mn, of the order of 0.1%, is enough to destroy superconductivity and to recover at low temperatures both the magnetic ground state and the orthorhombic structure of the pristine LaFeAsO parent compound. The results are discussed within a model where electron correlations enhance the Ruderman-Kittel-Kasuya-Yosida interaction among impurities.
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Affiliation(s)
- S Sanna
- Dipartimento di Fisica e Astronomia, Università di Bologna, via Berti-Pichat 6-2, I-40127 Bologna, Italy. CNR-SPIN Corso Perrone 24, I-16152 Genova, Italy
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8
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Kong P, Wang J, Jin Y, Zhang C, Lu C, Tian Y, Chen H. Exploration of high-pressure structural transition and electronic properties of BaFe 2S 3. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:115401. [PMID: 30557855 DOI: 10.1088/1361-648x/aaf8f8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The iron-based compound BaFe2S3 has received considerable attention in recent years due to its unique electronic properties with important applications. But, there has been relatively little attention devoted to the structure evolution of BaFe2S3 under high pressure. Here, we report a detailed theoretical study of the structural, electronic and sound velocity properties of BaFe2S3 under high pressure by CALYPSO structure search method in combination with the first-principles calculations. We have uncovered three novel structures of BaFe2S3 under high pressure with space group P2221, Imm2, and C2/m symmetries. Theoretical calculations reveal that the structures of BaFe2S3 under high pressure satisfy the phase transition sequence of Cmcm → P2221 → Imm2 → C2/m, and the corresponding transition pressures are 31.6, 47.4 and 57.0 GPa, respectively. Our results enrich the high pressure phases of BaFe2S3 and will stimulate future experiments to synthesize these new phases.
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Affiliation(s)
- Panlong Kong
- Department of Physics and Optoelectronic Engineering, Yangtze University, Jingzhou 434023, People's Republic of China. Department of Physics, Nanyang Normal University, Nanyang 473061, People's Republic of China. Center for High Pressure Science and Technology Advanced Research (HPSTAR), Beijing 100094, People's Republic of China
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9
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Miao J, Niu X, Jiang J, Peng R, Xie B, Chen F, Xu H, Feng D. Enhanced superconductivity of Ba 0.5K 0.5Fe 2As 2 under surface potassium dosing. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:455601. [PMID: 30251965 DOI: 10.1088/1361-648x/aae423] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Surface potassium dosing has been proven to be an effective method in tuning the electron doping and enhancing the superconducting transition temperatures in both iron chalcogenides and electron doped iron pnictides. However, it is not clear how surface potassium dosing affects the hole doping and superconductivity in hole doped Fe-based superconductors. Here we performed K-dosing on Ba0.5K0.5Fe2As2, a prototypical hole-doped iron pnictide compound, and explored the electronic structure by in situ angle-resolved photoemission spectroscopy measurements. Starting from the slightly over-doped Ba0.5K0.5Fe2As2, surface K-dosing effectively reduces the hole concentration towards optimal doping and enhances the superconductivity. Intriguingly, the enhancement of superconductivity does not slow down at optimal doping, and the gap further increases with K dosing even when the carrier doping effect is saturated. Meanwhile, the quasiparticle coherence of the inner hole pockets is enhanced by higher K dosing. Our results uncover a novel scattering-reduction effect of K-dosing in Ba1-x K x Fe2As2, which collaborates with the carrier doping effect and enhances superconductivity.
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Affiliation(s)
- Jin Miao
- State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200433, People's Republic of China. Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, People's Republic of China
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10
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Abstract
Iron-based superconductors display a variety of magnetic phases originating in the competition between electronic, orbital, and spin degrees of freedom. Previous theoretical investigations of the multi-orbital Hubbard model in one-dimension revealed the existence of an orbital-selective Mott phase (OSMP) with block spin order. Recent inelastic neutron scattering (INS) experiments on the BaFe2Se3 ladder compound confirmed the relevance of the block-OSMP. Moreover, the powder INS spectrum revealed an unexpected structure, containing both low-energy acoustic and high-energy optical modes. Here we present the theoretical prediction for the dynamical spin structure factor within a block-OSMP regime using the density-matrix renormalization-group method. In agreement with experiments, we find two dominant features: low-energy dispersive and high-energy dispersionless modes. We argue that the former represents the spin-wave-like dynamics of the block ferromagnetic islands, while the latter is attributed to a novel type of local on-site spin excitations controlled by the Hund coupling. Exploring the orbital-selective Mott phase (OSMP) addresses the central issue of electron correlations in the iron-based superconductors. Here the authors theoretically study the dynamical spin structure factor in the block-OSMP regime and unveil momentum dependent characteristics for different spin excitation modes.
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11
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Magnetic moment evolution and spin freezing in doped BaFe 2As 2. Sci Rep 2017; 7:8003. [PMID: 28808249 PMCID: PMC5556117 DOI: 10.1038/s41598-017-07286-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2016] [Accepted: 06/27/2017] [Indexed: 12/02/2022] Open
Abstract
Fe-Kβ X-ray emission spectroscopy measurements reveal an asymmetric doping dependence of the magnetic moments μbare in electron- and hole-doped BaFe2As2. At low temperature, μbare is nearly constant in hole-doped samples, whereas it decreases upon electron doping. Increasing temperature substantially enhances μbare in the hole-doped region, which is naturally explained by the theoretically predicted crossover into a spin-frozen state. Our measurements demonstrate the importance of Hund’s-coupling and electronic correlations, especially for hole-doped BaFe2As2, and the inadequacy of a fully localized or fully itinerant description of the 122 family of Fe pnictides.
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12
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Improving superconductivity in BaFe 2As 2-based crystals by cobalt clustering and electronic uniformity. Sci Rep 2017; 7:949. [PMID: 28424488 PMCID: PMC5430462 DOI: 10.1038/s41598-017-00984-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2016] [Accepted: 03/17/2017] [Indexed: 11/18/2022] Open
Abstract
Quantum materials such as antiferromagnets or superconductors are complex in that chemical, electronic, and spin phenomena at atomic scales can manifest in their collective properties. Although there are some clues for designing such materials, they remain mainly unpredictable. In this work, we find that enhancement of transition temperatures in BaFe2As2-based crystals are caused by removing local-lattice strain and electronic-structure disorder by thermal annealing. While annealing improves Néel-ordering temperature in BaFe2As2 crystal (TN = 132 K to 136 K) by improving in-plane electronic defects and reducing overall a-lattice parameter, it increases superconducting-ordering temperature in optimally cobalt-doped BaFe2As2 crystal (Tc = 23 to 25 K) by precipitating-out the cobalt dopants and giving larger overall a-lattice parameter. While annealing improves local chemical and electronic uniformity resulting in higher TN in the parent, it promotes nanoscale phase separation in the superconductor resulting in lower disparity and strong superconducting band gaps in the dominant crystal regions, which lead to both higher overall Tc and critical-current-density, Jc.
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Das P, Sangeetha NS, Pandey A, Benson ZA, Heitmann TW, Johnston DC, Goldman AI, Kreyssig A. Collinear antiferromagnetism in trigonal SrMn 2As 2 revealed by single-crystal neutron diffraction. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:035802. [PMID: 27845919 DOI: 10.1088/0953-8984/29/3/035802] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Iron pnictides and related materials have been a topic of intense research for understanding the complex interplay between magnetism and superconductivity. Here we report on the magnetic structure of SrMn2As2 that crystallizes in a trigonal structure ([Formula: see text]) and undergoes an antiferromagnetic (AFM) transition at [Formula: see text] K. The magnetic susceptibility remains nearly constant at temperatures [Formula: see text] with [Formula: see text] whereas it decreases significantly with [Formula: see text]. This shows that the ordered Mn moments lie in the [Formula: see text] plane instead of aligning along the [Formula: see text]-axis as in tetragonal BaMn2As2. Single-crystal neutron diffraction measurements on SrMn2As2 demonstrate that the Mn moments are ordered in a collinear Néel AFM phase with [Formula: see text] AFM alignment between a moment and all nearest neighbor moments in the basal plane and also perpendicular to it. Moreover, quasi-two-dimensional AFM order is manifested in SrMn2As2 as evident from the temperature dependence of the order parameter.
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Affiliation(s)
- Pinaki Das
- Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA
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14
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Xiang ZJ, Wang NZ, Wang AF, Zhao D, Sun ZL, Luo XG, Wu T, Chen XH. Incoherence-coherence crossover and low-temperature Fermi-liquid-like behavior in AFe2As2 (A = K, Rb, Cs): evidence from electrical transport properties. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:425702. [PMID: 27589485 DOI: 10.1088/0953-8984/28/42/425702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We study the normal-state transport properties of AFe2As2 (A = K, Rb and Cs) single crystals using Hall coefficient, resistivity and magnetoresistance (MR) measurements. In all three materials, the Hall coefficient R H shows a strong temperature dependence, which is typical for multi-band systems. In particular, R H develops an upturn below a characteristic temperature [Formula: see text], which is in agreement with the incoherence-coherence crossover reported in recent nuclear magnetic resonance studies. A Fermi-liquid-like state, characterized by T (2) behavior of the resistivity and a positive orbital MR obeying Kohler's rule, emerges below T FL ∼0.4 [Formula: see text]. The superconducting transition temperature T c experiences a simultaneous suppression with [Formula: see text] and T FL as the alkali ion's radius increases from A = K to A = Cs, suggesting that the unconventional superconductivity in the AFe2As2 series is related to the strength of the electronic coherence. A phase diagram, similar to that in the heavy fermion Kondo lattice system, is obtained. Based on all the experimental evidence, we argue that the physical properties of this family of heavily hole-doped Fe-based superconductors are controlled by the hybridization between itinerant carriers and localized orbitals, and the Kondo scenario could be effective in such a case.
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Affiliation(s)
- Z J Xiang
- Hefei National Laboratory for Physical Science at Microscale and Department of Physics, and Key Laboratory of Strongly-coupled Quantum Matter Physics, Chinese Academy of Sciences, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China
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15
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Ghosh S, Raghuvanshi N, Mohapatra S, Kumar A, Singh A. Multi-orbital quantum antiferromagnetism in iron pnictides-effective spin couplings and quantum corrections to sublattice magnetization. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:366002. [PMID: 27406889 DOI: 10.1088/0953-8984/28/36/366002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Effective spin couplings and spin fluctuation induced quantum corrections to sublattice magnetization are obtained in the [Formula: see text] AF state of a realistic three-orbital interacting electron model involving xz, yz and xy Fe 3d orbitals, providing insight into the multi-orbital quantum antiferromagnetism in iron pnictides. The xy orbital is found to be mainly responsible for the generation of strong ferromagnetic spin coupling in the b direction, which is critically important to fully account for the spin wave dispersion as measured in inelastic neutron scattering experiments. The ferromagnetic spin coupling is strongly suppressed as the xy band approaches half filling, and is ascribed to particle-hole exchange in the partially filled xy band. The strongest AF spin coupling in the a direction is found to be in the orbital off-diagonal sector involving the xz and xy orbitals. First order quantum corrections to sublattice magnetization are evaluated for the three orbitals, and yield a significant [Formula: see text] average reduction from the Hartree-Fock value.
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Affiliation(s)
- Sayandip Ghosh
- Department of Physics, Indian Institute of Technology Kanpur 208016, India
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16
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Ehlers G, Podlesnyak AA, Kolesnikov AI. The cold neutron chopper spectrometer at the Spallation Neutron Source-A review of the first 8 years of operation. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2016; 87:093902. [PMID: 27782573 DOI: 10.1063/1.4962024] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/28/2016] [Accepted: 08/20/2016] [Indexed: 06/06/2023]
Abstract
The first eight years of operation of the Cold Neutron Chopper Spectrometer (CNCS) at the Spallation Neutron Source in Oak Ridge is being reviewed. The instrument has been part of the facility user program since 2009, and more than 250 individual user experiments have been performed to date. CNCS is an extremely powerful and versatile instrument and offers leading edge performance in terms of beam intensity, energy resolution, and flexibility to trade one for another. Experiments are being routinely performed with the sample at extreme conditions: T ≲ 0.05 K, p ≳ 2 GPa, and B = 8 T can be achieved individually or in combination. In particular, CNCS is in a position to advance the state of the art with inelastic neutron scattering under pressure, and some of the recent accomplishments in this area will be presented in more detail.
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Affiliation(s)
- G Ehlers
- Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - A A Podlesnyak
- Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - A I Kolesnikov
- Chemical and Engineering Materials Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
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17
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Wang Z, Hu WJ, Nevidomskyy AH. Spin Ferroquadrupolar Order in the Nematic Phase of FeSe. PHYSICAL REVIEW LETTERS 2016; 116:247203. [PMID: 27367404 DOI: 10.1103/physrevlett.116.247203] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2016] [Indexed: 06/06/2023]
Abstract
We provide evidence that spin ferroquadrupolar (FQ) order is the likely ground state in the nonmagnetic nematic phase of stoichiometric FeSe. By studying the variational mean-field phase diagram of a bilinear-biquadratic Heisenberg model up to the 2nd nearest neighbor, we find the FQ phase in close proximity to the columnar antiferromagnet commonly realized in iron-based superconductors; the stability of the FQ phase is further verified by the density matrix renormalization group. The dynamical spin structure factor in the FQ state is calculated with flavor-wave theory, which yields a qualitatively consistent result with inelastic neutron scattering experiments on FeSe at both low and high energies. We verify that FQ can coexist with C_{4} breaking environments in the mean-field calculation, and further discuss the possibility that quantum fluctuations in FQ act as a source of nematicity.
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Affiliation(s)
- Zhentao Wang
- Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA
| | - Wen-Jun Hu
- Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA
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18
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Gonnelli RS, Daghero D, Tortello M, Ummarino GA, Bukowski Z, Karpinski J, Reuvekamp PG, Kremer RK, Profeta G, Suzuki K, Kuroki K. Fermi-Surface Topological Phase Transition and Horizontal Order-Parameter Nodes in CaFe2As2 Under Pressure. Sci Rep 2016; 6:26394. [PMID: 27216477 PMCID: PMC4877643 DOI: 10.1038/srep26394] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2016] [Accepted: 04/26/2016] [Indexed: 11/09/2022] Open
Abstract
Iron-based compounds (IBS) display a surprising variety of superconducting properties that seems to arise from the strong sensitivity of these systems to tiny details of the lattice structure. In this respect, systems that become superconducting under pressure, like CaFe2As2, are of particular interest. Here we report on the first directional point-contact Andreev-reflection spectroscopy (PCARS) measurements on CaFe2As2 crystals under quasi-hydrostatic pressure, and on the interpretation of the results using a 3D model for Andreev reflection combined with ab-initio calculations of the Fermi surface (within the density functional theory) and of the order parameter symmetry (within a random-phase-approximation approach in a ten-orbital model). The almost perfect agreement between PCARS results at different pressures and theoretical predictions highlights the intimate connection between the changes in the lattice structure, a topological transition in the holelike Fermi surface sheet, and the emergence on the same sheet of an order parameter with a horizontal node line.
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Affiliation(s)
- R S Gonnelli
- Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, 10129 Torino, Italy
| | - D Daghero
- Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, 10129 Torino, Italy
| | - M Tortello
- Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, 10129 Torino, Italy
| | - G A Ummarino
- Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, 10129 Torino, Italy
| | - Z Bukowski
- Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50-950 Wrocław, Poland
| | - J Karpinski
- Laboratory for Solid State Physics, Swiss Federal Institute of Technology (ETH), CH-8093 Zürich, Switzerland
| | - P G Reuvekamp
- Max Planck Institute for Solid State Research, D-70569 Stuttgart, Germany
| | - R K Kremer
- Max Planck Institute for Solid State Research, D-70569 Stuttgart, Germany
| | - G Profeta
- Dipartimento di Scienze Fisiche e Chimiche, Università dell'Aquila, 67100 Coppito (AQ), Italy
| | - K Suzuki
- Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - K Kuroki
- Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan
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19
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Lai X, Zhang H, Wang Y, Wang X, Zhang X, Lin J, Huang F. Observation of Superconductivity in Tetragonal FeS. J Am Chem Soc 2015; 137:10148-51. [DOI: 10.1021/jacs.5b06687] [Citation(s) in RCA: 148] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Xiaofang Lai
- Beijing
National Laboratory for Molecular Sciences and State Key Laboratory
of Rare Earth Materials Chemistry and Applications, College of Chemistry
and Molecular Engineering, Peking University, Beijing 100871, China
| | - Hui Zhang
- CAS
Key Laboratory of Materials for Energy Conversion and State Key Laboratory
of High Performance Ceramics and Superfine Microstructure, Shanghai
Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China
| | - Yingqi Wang
- Beijing
National Laboratory for Molecular Sciences and State Key Laboratory
of Rare Earth Materials Chemistry and Applications, College of Chemistry
and Molecular Engineering, Peking University, Beijing 100871, China
| | - Xin Wang
- Beijing
National Laboratory for Molecular Sciences and State Key Laboratory
of Rare Earth Materials Chemistry and Applications, College of Chemistry
and Molecular Engineering, Peking University, Beijing 100871, China
| | - Xian Zhang
- Beijing
National Laboratory for Molecular Sciences and State Key Laboratory
of Rare Earth Materials Chemistry and Applications, College of Chemistry
and Molecular Engineering, Peking University, Beijing 100871, China
| | - Jianhua Lin
- Beijing
National Laboratory for Molecular Sciences and State Key Laboratory
of Rare Earth Materials Chemistry and Applications, College of Chemistry
and Molecular Engineering, Peking University, Beijing 100871, China
| | - Fuqiang Huang
- Beijing
National Laboratory for Molecular Sciences and State Key Laboratory
of Rare Earth Materials Chemistry and Applications, College of Chemistry
and Molecular Engineering, Peking University, Beijing 100871, China
- CAS
Key Laboratory of Materials for Energy Conversion and State Key Laboratory
of High Performance Ceramics and Superfine Microstructure, Shanghai
Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China
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20
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Mourigal M, Wu S, Stone MB, Neilson JR, Caron JM, McQueen TM, Broholm CL. Block Magnetic Excitations in the Orbitally Selective Mott Insulator BaFe_{2}Se_{3}. PHYSICAL REVIEW LETTERS 2015; 115:047401. [PMID: 26252707 DOI: 10.1103/physrevlett.115.047401] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2014] [Indexed: 06/04/2023]
Abstract
Iron pnictides and selenides display a variety of unusual magnetic phases originating from the interplay between electronic, orbital, and lattice degrees of freedom. Using powder inelastic neutron scattering on the two-leg ladder BaFe_{2}Se_{3}, we fully characterize the static and dynamic spin correlations associated with the Fe_{4} block state, an exotic magnetic ground state observed in this low-dimensional magnet and in Rb_{0.89}Fe_{1.58}Se_{2}. All the magnetic excitations of the Fe_{4} block state predicted by an effective Heisenberg model with localized spins are observed below 300 meV and quantitatively reproduced. However, the data only account for 16(3)μ_{B}^{2} per Fe^{2+}, approximatively 2/3 of the total spectral weight expected for localized S=2 moments. Our results highlight how orbital degrees of freedom in iron-based magnets can conspire to stabilize an exotic magnetic state.
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Affiliation(s)
- M Mourigal
- Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - Shan Wu
- Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - M B Stone
- Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - J R Neilson
- Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - J M Caron
- Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - T M McQueen
- Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA
- Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - C L Broholm
- Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA
- Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
- Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA
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21
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Abstract
The interplay of superconductivity and magnetism is a subject of ongoing interest, stimulated most recently by the discovery of Fe-based superconductivity and the recognition that spin-fluctuations near a magnetic quantum critical point may provide an explanation for the superconductivity and the order parameter. Here we investigate magnetism in the Na filled Fe-based skutterudites using first principles calculations. NaFe4Sb12 is a known ferromagnet near a quantum critical point. We find a ferromagnetic metallic state for this compound driven by a Stoner type instability, consistent with prior work. In accord with prior work, the magnetization is overestimated, as expected for a material near an itinerant ferromagnetic quantum critical point. NaFe4P12 also shows a ferromagnetic instability at the density functional level, but this instability is much weaker than that of NaFe4Sb12, possibly placing it on the paramagnetic side of the quantum critical point. NaFe4As12 shows intermediate behavior. We also present results for skutterudite FeSb3, which is a metastable phase that has been reported in thin film form.
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22
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Mannella N. The magnetic moment enigma in Fe-based high temperature superconductors. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:473202. [PMID: 25352180 DOI: 10.1088/0953-8984/26/47/473202] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The determination of the most appropriate starting point for the theoretical description of Fe-based materials hosting high-temperature superconductivity remains among the most important unsolved problem in this relatively new field. Most of the work to date has focused on the pnictides, with LaFeAsO, BaFe(2)As(2) and LiFeAs being representative parent compounds of three families known as 1111, 122 and 111, respectively. This topical review examines recent progress in this area, with particular emphasis on the implication of experimental data which have provided evidence for the presence of electron itinerancy and the detection of local spin moments. In light of the results presented, the necessity of a theoretical framework contemplating the presence and the interplay between itinerant electrons and large spin moments is discussed. It is argued that the physics at the heart of the macroscopic properties of pnictides Fe-based high-temperature superconductors appears to be far more complex and interesting than initially predicted.
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Affiliation(s)
- Norman Mannella
- Department of Physics and Astronomy, University of Tennessee, Knoxville, TN,USA
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23
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Cantoni C, Mitchell JE, May AF, McGuire MA, Idrobo JC, Berlijn T, Dagotto E, Chisholm MF, Zhou W, Pennycook SJ, Sefat AS, Sales BC. Orbital occupancy and charge doping in iron-based superconductors. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2014; 26:6193-6198. [PMID: 25070045 DOI: 10.1002/adma.201401518] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2014] [Revised: 06/05/2014] [Indexed: 06/03/2023]
Abstract
The intrinsic Fe local magnetic moment and Fe orbital occupations of iron-based superconductors are unveiled through the local, real-space capability of aberration-corrected scanning transmission electron microscopy/electron energy loss spectroscopy (STEM/EELS). Although the ordering of Fe moments needs to be suppressed for superconductivity to arise, the local, fluctuating Fe magnetic moment is enhanced near optimal superconductivity.
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Affiliation(s)
- Claudia Cantoni
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
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24
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Enayat M, Sun Z, Singh UR, Aluru R, Schmaus S, Yaresko A, Liu Y, Lin C, Tsurkan V, Loidl A, Deisenhofer J, Wahl P. Real-space imaging of the atomic-scale magnetic structure of Fe
1+
y
Te. Science 2014; 345:653-6. [DOI: 10.1126/science.1251682] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- Mostafa Enayat
- Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
| | - Zhixiang Sun
- Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
| | - Udai Raj Singh
- Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
| | - Ramakrishna Aluru
- Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
| | - Stefan Schmaus
- Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
| | - Alexander Yaresko
- Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
| | - Yong Liu
- Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
| | - Chengtian Lin
- Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
| | - Vladimir Tsurkan
- Center for Electronic Correlations and Magnetism, Experimental Physics V, University of Augsburg, D-86159 Augsburg, Germany
- Institute of Applied Physics, Academy of Sciences of Moldova, MD 2028, Chisinau, Republica Moldova
| | - Alois Loidl
- Center for Electronic Correlations and Magnetism, Experimental Physics V, University of Augsburg, D-86159 Augsburg, Germany
| | - Joachim Deisenhofer
- Center for Electronic Correlations and Magnetism, Experimental Physics V, University of Augsburg, D-86159 Augsburg, Germany
| | - Peter Wahl
- Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
- Scottish Universities Physics Alliance, School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9SS, UK
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25
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Charnukha A. Optical conductivity of iron-based superconductors. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:253203. [PMID: 24899620 DOI: 10.1088/0953-8984/26/25/253203] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
The new family of unconventional iron-based superconductors discovered in 2006 immediately relieved their copper-based high-temperature predecessors as the most actively studied superconducting compounds in the world. The experimental and theoretical effort made in order to unravel the mechanism of superconductivity in these materials has been overwhelming. Although our understanding of their microscopic properties has been improving steadily, the pairing mechanism giving rise to superconducting transition temperatures up to 55 K remains elusive. And yet the hope is strong that these materials, which possess a drastically different electronic structure but similarly high transition temperatures compared to the copper-based compounds, will shed essential new light onto the several-decade-old problem of unconventional superconductivity. In this work we review the current understanding of the itinerant-charge-carrier dynamics in the iron-based superconductors and parent compounds largely based on the optical conductivity data the community has gleaned over the past seven years using such experimental techniques as reflectivity, ellipsometry, and terahertz transmission measurements and analyze the implications of these studies for the microscopic properties of the iron-based materials as well as the mechanism of superconductivity therein.
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26
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Avci S, Chmaissem O, Allred J, Rosenkranz S, Eremin I, Chubukov A, Bugaris D, Chung D, Kanatzidis M, Castellan JP, Schlueter J, Claus H, Khalyavin D, Manuel P, Daoud-Aladine A, Osborn R. Magnetically driven suppression of nematic order in an iron-based superconductor. Nat Commun 2014; 5:3845. [DOI: 10.1038/ncomms4845] [Citation(s) in RCA: 138] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2013] [Accepted: 04/08/2014] [Indexed: 11/09/2022] Open
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27
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Fobes D, Zaliznyak IA, Xu Z, Zhong R, Gu G, Tranquada JM, Harriger L, Singh D, Garlea VO, Lumsden M, Winn B. Ferro-orbital ordering transition in iron telluride Fe(1+y)Te. PHYSICAL REVIEW LETTERS 2014; 112:187202. [PMID: 24856717 DOI: 10.1103/physrevlett.112.187202] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2013] [Indexed: 06/03/2023]
Abstract
Fe(1+y)Te with y≲0.05 exhibits a first-order phase transition on cooling to a state with a lowered structural symmetry, bicollinear antiferromagnetic order, and metallic conductivity, dρ/dT>0. Here, we study samples with y=0.09(1), where the frustration effects of the interstitial Fe decouple different orders, leading to a sequence of transitions. While the lattice distortion is closely followed by incommensurate magnetic order, the development of bicollinear order and metallic electronic coherence is uniquely associated with a separate hysteretic first-order transition, at a markedly lower temperature, to a phase with dramatically enhanced bond-order wave (BOW) order. The BOW state suggests ferro-orbital ordering, where electronic delocalization in ferromagnetic zigzag chains decreases local spin and results in metallic transport.
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Affiliation(s)
- David Fobes
- CMPMSD, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Igor A Zaliznyak
- CMPMSD, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Zhijun Xu
- CMPMSD, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Ruidan Zhong
- CMPMSD, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Genda Gu
- CMPMSD, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - John M Tranquada
- CMPMSD, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Leland Harriger
- NCNR, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - Deepak Singh
- NCNR, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - V Ovidiu Garlea
- QCMD, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Mark Lumsden
- QCMD, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Barry Winn
- QCMD, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
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28
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Gaczyński P, Klimczuk T, Walker H, Springell R, Colineau E, Eloirdi R, Griveau JC, Caciuffo R. (237)Np Mössbauer effect study on NpFeAsO. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:156002. [PMID: 24675054 DOI: 10.1088/0953-8984/26/15/156002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We report (237)Np Mössbauer measurements on NpFeAsO. The Np atoms were found to occupy only one crystallographic site. The value of the isomer shift (δ ∼ 9.1 mm s(-1) versus NpAl2) indicates a 5f(4) electronic configuration (Np(3+) ions). The magnetic ordering of the Np sublattice below 60 K is established and the saturated ordered magnetic moment is determined to be 1.73μB at 3.6 K. The unique set of hyperfine parameters exclude a modulated magnetic structure or spin waves on the Np site. The neptunium magnetic moments μNp are found to lie along the tetragonal c-axis.
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Affiliation(s)
- P Gaczyński
- European Commission, JRC, Institute for Transuranium Elements, Postfach 2340, 76125 Karlsruhe, Germany. Institute of Physical and Theoretical Chemistry, Technische Universität Braunschweig, Hans-Sommer-Str. 10, D-38106 Braunschweig, Germany
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29
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Song CL, Wang YL, Jiang YP, Li Z, Wang L, He K, Chen X, Hoffman JE, Ma XC, Xue QK. Imaging the electron-boson coupling in superconducting FeSe films using a scanning tunneling microscope. PHYSICAL REVIEW LETTERS 2014; 112:057002. [PMID: 24580624 DOI: 10.1103/physrevlett.112.057002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2013] [Indexed: 06/03/2023]
Abstract
Scanning tunneling spectroscopy has been used to reveal signatures of a bosonic mode in the local quasiparticle density of states of superconducting FeSe films. The mode appears below Tc as a "dip-hump" feature at energy Ω∼4.7kBTc beyond the superconducting gap Δ. Spectra on strained regions of the FeSe films reveal simultaneous decreases in Δ and Ω. This contrasts with all previous reports on other high-Tc superconductors, where Δ locally anticorrelates with Ω. A local strong coupling model is found to reconcile the discrepancy well, and to provide a unified picture of the electron-boson coupling in unconventional superconductors.
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Affiliation(s)
- Can-Li Song
- State Key Laboratory for Surface Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China and State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China and Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Yi-Lin Wang
- State Key Laboratory for Surface Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Ye-Ping Jiang
- State Key Laboratory for Surface Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China and State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
| | - Zhi Li
- State Key Laboratory for Surface Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Lili Wang
- State Key Laboratory for Surface Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Ke He
- State Key Laboratory for Surface Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Xi Chen
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
| | - Jennifer E Hoffman
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Xu-Cun Ma
- State Key Laboratory for Surface Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Qi-Kun Xue
- State Key Laboratory for Surface Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China and State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
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30
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Soh JH, Tucker GS, Pratt DK, Abernathy DL, Stone MB, Ran S, Bud'ko SL, Canfield PC, Kreyssig A, McQueeney RJ, Goldman AI. Inelastic neutron scattering study of a nonmagnetic collapsed tetragonal phase in nonsuperconducting CaFe2As2: evidence of the impact of spin fluctuations on superconductivity in the iron-arsenide compounds. PHYSICAL REVIEW LETTERS 2013; 111:227002. [PMID: 24329466 DOI: 10.1103/physrevlett.111.227002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2013] [Indexed: 06/03/2023]
Abstract
The relationship between antiferromagnetic spin fluctuations and superconductivity has become a central topic of research in studies of superconductivity in the iron pnictides. We present unambiguous evidence of the absence of magnetic fluctuations in the nonsuperconducting collapsed tetragonal phase of CaFe2As2 via inelastic neutron scattering time-of-flight data, which is consistent with the view that spin fluctuations are a necessary ingredient for unconventional superconductivity in the iron pnictides. We demonstrate that the collapsed tetragonal phase of CaFe2As2 is nonmagnetic, and discuss this result in light of recent reports of high-temperature superconductivity in the collapsed tetragonal phase of closely related compounds.
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Affiliation(s)
- J H Soh
- Ames Laboratory, U.S. Department of Energy and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | - G S Tucker
- Ames Laboratory, U.S. Department of Energy and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | - D K Pratt
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - D L Abernathy
- Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - M B Stone
- Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - S Ran
- Ames Laboratory, U.S. Department of Energy and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | - S L Bud'ko
- Ames Laboratory, U.S. Department of Energy and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | - P C Canfield
- Ames Laboratory, U.S. Department of Energy and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | - A Kreyssig
- Ames Laboratory, U.S. Department of Energy and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | - R J McQueeney
- Ames Laboratory, U.S. Department of Energy and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | - A I Goldman
- Ames Laboratory, U.S. Department of Energy and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
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31
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Taylor AE, Ewings RA, Perring TG, Parker DR, Ollivier J, Clarke SJ, Boothroyd AT. Absence of strong magnetic fluctuations in FeP-based systems LaFePO and Sr₂ScO₃FeP. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2013; 25:425701. [PMID: 24065357 DOI: 10.1088/0953-8984/25/42/425701] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We report neutron inelastic scattering measurements on polycrystalline LaFePO and Sr2ScO3FeP, two members of the iron phosphide families of superconductors. No evidence is found for any magnetic fluctuations in the spectrum of either material in the energy and wavevector ranges probed. Special attention is paid to the wavevector at which spin-density-wave-like fluctuations are seen in other iron-based superconductors. We estimate that the magnetic signal, if present, is at least a factor of four (Sr2ScO3FeP) or seven (LaFePO) smaller than in the related iron arsenide and chalcogenide superconductors. These results suggest that magnetic fluctuations are not as influential on the electronic properties of the iron phosphide systems as they are in other iron-based superconductors.
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Affiliation(s)
- A E Taylor
- Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, UK
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32
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Presniakov I, Morozov I, Sobolev A, Roslova M, Boltalin A, Son V, Volkova O, Vasiliev A, Wurmehl S, Büchner B. Local structure and hyperfine interactions of 57Fe in NaFeAs studied by Mössbauer spectroscopy. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2013; 25:346003. [PMID: 23913008 DOI: 10.1088/0953-8984/25/34/346003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Detailed 57Fe Mössbauer spectroscopy measurements on superconducting NaFeAs powder samples have been performed in the temperature range 13 K ≤ T < 300 K. The 57Fe spectra recorded in the paramagnetic range (T > TN ≈ 46 K) are discussed supposing that most of the Fe2+ ions are located in distorted (FeAs4) tetrahedra of NaFeAs phase, while an additional minor (<10%) component of the spectra corresponds to impurity or intergrowth NaFe2As2 phase with a nominal composition near NaFe2As2. Our results reveal that the structural transition (TS ≈ 55 K) has a weak effect on the electronic structure of iron ions, while at T ≤ TN the spectra show a continuous distribution of hyperfine fields HFe. The shape of these spectra is analyzed in terms of two models: (i) an incommensurate spin density wave modulation of iron magnetic structure, (ii) formation of a microdomain structure or phase separation. It is shown that the hyperfine parameters obtained using these two methods have very similar values over the whole temperature range. Analysis of the temperature dependence HFe(T) with the Bean–Rodbell model leads to ζ = 1.16 ± 0.05, suggesting that the magnetic phase transition is first order in nature. A sharp evolution of the VZZ(T) and η(T) parameters of the full Hamiltonian of hyperfine interactions near T ≈ (TN,TS) is interpreted as a manifestation of the anisotropic electron redistribution between the dxz-, dyz- and dxy-orbitals of the iron ions.
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Affiliation(s)
- I Presniakov
- Lomonosov Moscow State University, Moscow, 119992 Leninskie Gory, Moscow, Russia
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33
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Baek SH, Harnagea L, Wurmehl S, Büchner B, Grafe HJ. Anomalous superconducting state in LiFeAs implied by the 75As Knight shift measurement. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2013; 25:162204. [PMID: 23553364 DOI: 10.1088/0953-8984/25/16/162204] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
(75)As NMR investigation of a single crystal of superconducting LiFeAs is presented. The Knight shift and the in situ ac susceptibility measurements as a function of temperature and external field are indicative of two superconducting (SC) transition temperatures, each of which is associated with its own upper critical field. Strikingly, the Knight shift maintains its normal state value over a temperature range in the SC state before it drops abruptly, being consistent with spin-singlet pairing. Together with our previous NMR study, the anomalous SC state featuring the constant Knight shift is attributed to the extremely sensitive SC properties of LiFeAs, probably stemming from its proximity to a critical instability.
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Affiliation(s)
- S-H Baek
- IFW-Dresden, Institute for Solid State Research, Dresden, Germany.
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34
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Chen JM, Haw SC, Lee JM, Chen SA, Lu KT, Deng MJ, Chen SW, Ishii H, Hiraoka N, Tsuei KD. Electronic structure and characteristics of Fe 3d valence states of Fe(1.01)Se superconductors under pressure probed by x-ray absorption spectroscopy and resonant x-ray emission spectroscopy. J Chem Phys 2012; 137:244702. [PMID: 23277947 DOI: 10.1063/1.4772466] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The electronic structure and characteristics of Fe 3d valence states of iron-chalcogenide Fe(1.01)Se superconductors under pressure were probed with x-ray absorption spectroscopy and resonant x-ray emission spectroscopy (RXES). The intensity of the pre-edge peak at ~7112.7 eV of the Fe K-edge x-ray absorption spectrum of Fe(1.01)Se decreases for pressure from 0.5 GPa increased to 6.9 GPa. The satellite line Kβ' was reduced in intensity upon applying pressure and became absent for pressure 52 GPa. Fe(1.01)Se shows a small net magnetic moment of Fe(2+), likely arising from strong Fe-Fe spin fluctuations. The 1s3p-RXES spectra of Fe(1.01)Se at pressures 0.5, 6.9, and 52 GPa recorded at the Fe K-edge reveal that unoccupied Fe 3d states exhibit a delocalized character, stemming from hybridization of Fe 3d and 4p orbitals arising from a local distortion around the Fe atom in a tetrahedral site. Application of pressure causes suppression of this on-site Fe 3d-Fe 4p hybridization, and thereby decreases the intensity of the pre-edge feature in the Fe K-edge absorption spectrum of Fe(1.01)Se. Compression enhances spin fluctuations at Fe sites in Fe(1.01)Se and increases the corresponding T(c), through a competition between nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic superexchange interactions. This result aids our understanding of the physics underlying iron-based superconductors.
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Affiliation(s)
- J M Chen
- National Synchrotron Radiation Research Center, Hsinchu, Taiwan.
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35
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Peng H, De D, Wu Z, Diaz-Pinto C. Observation of multiple superconducting gaps in Fe₁+yTe₁-xSex via a nanoscale approach to point-contact spectroscopy. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2012; 24:455703. [PMID: 23092957 DOI: 10.1088/0953-8984/24/45/455703] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We report a novel experimental approach to point-contact Andreev reflection spectroscopy with diagnostic capability via a unique design for nanoscale normal metal/superconductor devices with excellent thermomechanical stability, and have employed this method to unveil the existence of two superconducting energy gaps in iron chalcogenide Fe(1+y)Te(1-x)Se(x), which is crucial for understanding its pairing mechanism. This work opens up new opportunities to study gap structures in superconductors and elemental excitations in solids.
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Affiliation(s)
- Haibing Peng
- Department of Physics and the Texas Center for Superconductivity, University of Houston, 4800 Calhoun Road, Houston, TX 77204-5005, USA.
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36
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Kim MG, Lamsal J, Heitmann TW, Tucker GS, Pratt DK, Khan SN, Lee YB, Alam A, Thaler A, Ni N, Ran S, Bud'ko SL, Marty KJ, Lumsden MD, Canfield PC, Harmon BN, Johnson DD, Kreyssig A, McQueeney RJ, Goldman AI. Effects of transition metal substitutions on the incommensurability and spin fluctuations in BaFe2As2 by elastic and inelastic neutron scattering. PHYSICAL REVIEW LETTERS 2012; 109:167003. [PMID: 23215117 DOI: 10.1103/physrevlett.109.167003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2012] [Indexed: 06/01/2023]
Abstract
The spin fluctuation spectra from nonsuperconducting Cu-substituted, and superconducting Co-substituted, BaFe(2)As(2) are compared quantitatively by inelastic neutron scattering measurements and are found to be indistinguishable. Whereas diffraction studies show the appearance of incommensurate spin-density wave order in Co and Ni substituted samples, the magnetic phase diagram for Cu substitution does not display incommensurate order, demonstrating that simple electron counting based on rigid-band concepts is invalid. These results, supported by theoretical calculations, suggest that substitutional impurity effects in the Fe plane play a significant role in controlling magnetism and the appearance of superconductivity, with Cu distinguished by enhanced impurity scattering and split-band behavior.
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Affiliation(s)
- M G Kim
- Ames Laboratory, U.S. DOE, Ames, Iowa 50011, USA
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37
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May AF, McGuire MA, Cao H, Sergueev I, Cantoni C, Chakoumakos BC, Parker DS, Sales BC. Spin reorientation in TlFe1.6Se2 with complete vacancy ordering. PHYSICAL REVIEW LETTERS 2012; 109:077003. [PMID: 23006396 DOI: 10.1103/physrevlett.109.077003] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/29/2012] [Indexed: 06/01/2023]
Abstract
The relationship between vacancy ordering and magnetism in TlFe(1.6)Se(2) has been investigated via single crystal neutron diffraction, nuclear forward scattering, and transmission electron microscopy. The examination of chemically and structurally homogeneous crystals allows the true ground state to be revealed, which is characterized by Fe moments lying in the ab plane below 100 K. This is in sharp contrast to crystals containing regions of order and disorder, where a competition between c axis and ab plane orientations of the moments is observed. The properties of partially disordered TlFe(1.6)Se(2) are, therefore, not associated with solely the ordered or disordered regions. This contrasts the viewpoint that phase separation results in independent physical properties in intercalated iron selenides, suggesting a coupling between ordered and disordered regions may play an important role in the superconducting analogues.
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Affiliation(s)
- Andrew F May
- Materials Science and Technology Division, Oak Ridge National Laboratory, Tennessee 37831, USA
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38
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Carpenter MA, Zhang Z, Howard CJ. A linear-quadratic order parameter coupling model for magnetoelastic phase transitions in Fe(1-x)O and MnO. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2012; 24:156002. [PMID: 22418618 DOI: 10.1088/0953-8984/24/15/156002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The combined structural and antiferromagnetic phase transition in wüstite, Fe(1-x)O, at the Néel temperature, T(N) ~ 195 K, is treated in terms of coupling between two macroscopic order parameters related to separate discrete instabilities. These each couple with a rhombohedral shear strain to give an indirect mechanism of linear (structural)-quadratic (magnetic) coupling between them. Based on patterns of lattice parameter and magnetic ordering data from the literature, it appears that the overall behaviour matches the general pattern of linear-quadratic coupling for a system with two rather similar instability temperatures. At low pressures, the magnetic instability occurs at a higher temperature than the structural instability but the coupling results in a single phase transition dominated by the influence of the magnetic order parameter. For Fe(0.99)O the magnetic order parameter, m, varies with temperature as ~m(8) ∝ (T(N) - T), while for Fe(0.94)O the temperature dependence is of ~m(4) or ~m(2). It is proposed that, with increasing pressure, there is a crossover of instability temperatures such that the structural instability occurs first at pressures above ~13 GPa. This would be expected to give rise to a first-order phase transition, as appears to occur, but magnetic ordering would still occur simultaneously if the coupling is sufficiently strong. Symmetry analysis and comparison with the behaviour of MnO shows that there are a number of different possible magnetically ordered structures which could be stabilized by pressure or non-hydrostatic stress to give topologically rich phase diagrams.
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Affiliation(s)
- Michael A Carpenter
- Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK
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Zaliznyak IA, Xu Z, Tranquada JM, Gu G, Tsvelik AM, Stone MB. Unconventional temperature enhanced magnetism in Fe1.1Te. PHYSICAL REVIEW LETTERS 2011; 107:216403. [PMID: 22181901 DOI: 10.1103/physrevlett.107.216403] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2011] [Indexed: 05/15/2023]
Abstract
Our inelastic neutron scattering study of spin excitations in iron telluride reveals remarkable thermal evolution of the collective magnetism. In the temperature range relevant for the superconductivity in FeTe(1-x)Se(x) materials, where the local-moment behavior is dominated by liquidlike correlations of emergent spin plaquettes, we observe unusual, marked increase of magnetic fluctuations upon heating. The effective spin per Fe at T ≈ 10 K, in the phase with weak antiferromagnetic order, corresponds to S ≈ 1, consistent with the recent analyses that emphasize importance of Hund's coupling [K. Haule and G. Kotliar, New J. Phys. 11, 025021 (2009).]. However, it grows to S ≈ 3/2 in the high-T disordered phase, suggestive of the Kondo-type behavior, where local magnetic moments are entangled with the itinerant electrons.
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Affiliation(s)
- Igor A Zaliznyak
- CMPMSD, Brookhaven National Laboratory, Upton, New York 11973, USA.
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40
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Paulose PL, Ramakrishnan S, Hossain Z. Doping dependent evolution of magnetism and superconductivity in Eu(1-x)K(x)Fe2As2 (x = 0-1) and temperature dependence of the lower critical field H(c1). JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:455702. [PMID: 22019495 DOI: 10.1088/0953-8984/23/45/455702] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We have synthesized polycrystalline samples of Eu(1-x)K(x)Fe2As2 (x = 0-1) and carried out systematic characterization using x-ray diffraction, ac and dc magnetic susceptibility, and electrical resistivity measurements. A clear signature of the coexistence of a superconducting transition (T(c) = 5.5 K) with spin density wave (SDW) ordering is observed in our underdoped sample with x = 0.15. The SDW transition disappears completely for the x = 0.3 sample and superconductivity arises below 20 K. The superconducting transition temperature Tc increases with increase in the K content and a maximum Tc = 33 K is reached for x = 0.5, beyond which it decreases again. The doping dependent Tx phase diagram is extracted from the magnetic and electrical transport data. It is found that magnetic ordering of Eu moments coexists with the superconductivity up to x = 0.6. The isothermal magnetization data taken at 2 K for the doped samples suggest the 2+ valence state of the Eu ions. We also present the temperature dependence of the lower critical field H(c1) of the superconducting polycrystalline samples. The values of H(c1)(0) obtained for x = 0.3, 0.5, and 0.7 after taking the demagnetization factor into account are 202, 330, and 212 Oe, respectively. The London penetration depth λ(T) calculated from the lower critical field does not show exponential dependence at low temperature, as would be expected for a fully gapped clean s-wave superconductor. In contrast, it shows a T2 power law feature up to T = 0.3Tc, as observed in Ba(1-x)K(x)Fe2As2 and BaFe(2-x)Co(x)As2.
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41
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d-Wave Superconductivity and s-Wave Charge Density Waves: Coexistence between Order Parameters of Different Origin and Symmetry. Symmetry (Basel) 2011. [DOI: 10.3390/sym3040699] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
A review of the theory describing the coexistence between d-wave superconductivity and s-wave charge-density-waves (CDWs) is presented. The CDW gapping is identified with pseudogapping observed in high-Tc oxides. According to the cuprate specificity, the analysis is carried out for the two-dimensional geometry of the Fermi surface (FS). Phase diagrams on the σ0 − α plane—here, σ0 is the ratio between the energy gaps in the parent pure CDW and superconducting states, and the quantity 2α is connected with the degree of dielectric (CDW) FS gapping—were obtained for various possible configurations of the order parameters in the momentum space. Relevant tunnel and photoemission experimental data for high-Tc oxides are compared with theoretical predictions. A brief review of the results obtained earlier for the coexistence between s-wave superconductivity and CDWs is also given.
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42
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Khasanov A, Jiang J, Hellstrom EE, Nath A. Origin of the dynamics of the spin state in undoped BaFe2As2: Mössbauer studies. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:342201. [PMID: 21841224 DOI: 10.1088/0953-8984/23/34/342201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Fe-As based superconductors provide a good system for understanding the relationship between magnetism and superconductivity. Considerable efforts have been expended in understanding the magnetic behavior of the parent compound, BaFe2As2. However, it had not been realized that traces of adsorbed O2 by the material bring about drastic changes in its magnetic behavior. O2 is known to trap electrons, forming O2(-). Guided by this discovery, we observe in the absence of O2 a dynamic transition between intermediate and low spin states of Fe and hysteresis effects, and in the presence of O2 trapping of the magnetic state. These observations are likely to have a bearing on the role of magnetism in superconductivity.
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Affiliation(s)
- Airat Khasanov
- Department of Chemistry, University of North Carolina, Asheville, NC 28804, USA
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43
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Joseph B, Iadecola A, Malavasi L, Saini NL. Temperature-dependent local structure of NdFeAsO(1-x)F(x) system using arsenic K-edge extended x-ray absorption fine structure. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:265701. [PMID: 21666306 DOI: 10.1088/0953-8984/23/26/265701] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Local structure of NdFeAsO(1-x)F(x) (x = 0.0, 0.05, 0.15 and 0.18) high temperature iron-pnictide superconductor system is studied using arsenic K-edge extended x-ray absorption fine structure measurements as a function of temperature. Fe-As bond length shows only a weak temperature and F-substitution dependence, consistent with the strong covalent nature of this bond. The temperature dependence of the mean square relative displacements of the Fe-As bond length are well described by the correlated Einstein model for all the samples, but with different Einstein temperatures for the superconducting and non-superconducting samples. The results indicate distinct local Fe-As lattice dynamics in the superconducting and non-superconducting iron-pnictide systems.
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Affiliation(s)
- B Joseph
- Dipartimento di Chimica, Sezione di Chimica Fisica, INSTM (UdR Pavia), Università di Pavia, Viale Taramelli 16, 27100 Pavia, Italy
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Brydon PMR, Daghofer M, Timm C. Magnetic order in orbital models of the iron pnictides. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:246001. [PMID: 21613725 DOI: 10.1088/0953-8984/23/24/246001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We examine the appearance of the experimentally observed stripe spin-density-wave magnetic order in five different orbital models of the iron pnictide parent compounds. A restricted mean-field ansatz is used to determine the magnetic phase diagram of each model. Using the random phase approximation, we then check this phase diagram by evaluating the static spin susceptibility in the paramagnetic state close to the mean-field phase boundaries. The momenta for which the susceptibility is peaked indicate in an unbiased way the actual ordering vector of the nearby mean-field state. The dominant orbitally resolved contributions to the spin susceptibility are also examined to determine the origin of the magnetic instability. We find that the observed stripe magnetic order is possible in four of the models, but it is extremely sensitive to the degree of nesting between the electron and hole Fermi pockets. In the more realistic five-orbital models, this order competes with a strong-coupling incommensurate state which appears to be controlled by details of the electronic structure below the Fermi energy. We conclude by discussing the implications of our work for the origin of the magnetic order in the pnictides.
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Affiliation(s)
- P M R Brydon
- Institut für Theoretische Physik, Technische Universität Dresden, Dresden, Germany.
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45
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Khasanov A, Bhargava SC, Stevens JG, Jiang J, Weiss JD, Hellstrom EE, Nath A. Mössbauer studies of the superconducting cobalt/nickel-doped BaFe2As2. Whither go the injected electron(s)? JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:202201. [PMID: 21540518 DOI: 10.1088/0953-8984/23/20/202201] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Mössbauer studies of cobalt- and nickel-doped BaFe(2)As(2) show that the s-electron density at the (57)Fe nuclei, as measured by the isomer shift, is the same as that for the parent BaFe(2)As(2). Apparently, the electron population of the d shell, which shields the s-electron density at the nuclei, remains unchanged. We invoke the involvement of p-orbital hybridization with the d orbital in Fe-As bonding. Furthermore, the shrinkage of the lattice on substitution enhances the As-As sp hybridization, providing a path for the migration of additional electrons. The proposed mechanism is consistent with Hall coefficient and thermoelectric effect measurements.
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Affiliation(s)
- Airat Khasanov
- Department of Chemistry, University of North Carolina, Asheville, NC 28804, USA
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46
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Das T, Balatsky AV. Two energy scales in the magnetic resonance spectrum of electron and hole doped pnictide superconductors. PHYSICAL REVIEW LETTERS 2011; 106:157004. [PMID: 21568605 DOI: 10.1103/physrevlett.106.157004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2010] [Indexed: 05/30/2023]
Abstract
We argue that a multiband superconductor with sign-changing gaps may have multiple spin resonances. We calculate the RPA-based spin resonance spectra of a pnictide superconductor by using the five-band tight-binding model or angle-resolved photoemission spectroscopy Fermi surface (FS) and experimental values of superconducting gaps. The resonance spectra split in both energy and momenta due to the effects of multiband and multiple gaps in s(±) pairing; the higher energy peak appears around the commensurate momenta due to scattering between α-FS to γ/δ-FS pockets. The second resonance is incommensurate, coming from β-FS to γ/δ-FS scatterings, and its q vector is doping-dependent and, hence, on the FS topology. Energies of both resonances ω(res)(1,2) are strongly doping-dependent and are proportional to the gap amplitudes at the contributing FSs.
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Affiliation(s)
- Tanmoy Das
- Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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47
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48
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Shermadini Z, Krzton-Maziopa A, Bendele M, Khasanov R, Luetkens H, Conder K, Pomjakushina E, Weyeneth S, Pomjakushin V, Bossen O, Amato A. Coexistence of magnetism and superconductivity in the iron-based compound Cs0.8(FeSe0.98)2. PHYSICAL REVIEW LETTERS 2011; 106:117602. [PMID: 21469895 DOI: 10.1103/physrevlett.106.117602] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2011] [Indexed: 05/30/2023]
Abstract
We report on muon-spin rotation and relaxation (μSR), electrical resistivity, magnetization and differential scanning calorimetry measurements performed on a high-quality single crystal of Cs(0.8)(FeSe(0.98))(2). Whereas our transport and magnetization data confirm the bulk character of the superconducting state below T(c)=29.6(2) K, the μSR data indicate that the system is magnetic below T(N)=478.5(3) K, where a first-order transition occurs. The first-order character of the magnetic transition is confirmed by differential scanning calorimetry data. Taken all together, these data indicate in Cs(0.8)(FeSe(0.98))(2) a microscopic coexistence between the superconducting phase and a strong magnetic phase. The observed T(N) is the highest reported to date for a magnetic superconductor.
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Affiliation(s)
- Z Shermadini
- Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
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49
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Yin WG, Lee CC, Ku W. Unified picture for magnetic correlations in iron-based superconductors. PHYSICAL REVIEW LETTERS 2010; 105:107004. [PMID: 20867542 DOI: 10.1103/physrevlett.105.107004] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2010] [Indexed: 05/29/2023]
Abstract
The varying metallic antiferromagnetic correlations observed in iron-based superconductors are unified in a model consisting of both itinerant electrons and localized spins. The decisive factor is found to be the sensitive competition between the superexchange antiferromagnetism and the orbital-degenerate double-exchange ferromagnetism. Our results reveal the crucial role of Hund's rule coupling for the strongly correlated nature of the system and suggest that the iron-based superconductors are closer kin to manganites than cuprates in terms of their diverse magnetism and incoherent normal-state electron transport. This unified picture would be instrumental for exploring other exotic properties and the mechanism of superconductivity in this new class of superconductors.
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Affiliation(s)
- Wei-Guo Yin
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
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