1
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Noad HML, Ishida K, Li YS, Gati E, Stangier V, Kikugawa N, Sokolov DA, Nicklas M, Kim B, Mazin II, Garst M, Schmalian J, Mackenzie AP, Hicks CW. Giant lattice softening at a Lifshitz transition in Sr 2RuO 4. Science 2023; 382:447-450. [PMID: 37883549 DOI: 10.1126/science.adf3348] [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] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2022] [Accepted: 09/16/2023] [Indexed: 10/28/2023]
Abstract
The interplay of electronic and structural degrees of freedom in solids is a topic of intense research. More than 60 years ago, Lifshitz discussed a counterintuitive possibility: lattice softening driven by conduction electrons at topological Fermi surface transitions. The effect that he predicted, however, was small and has not been convincingly observed. Using a piezo-based uniaxial pressure cell to tune the ultraclean metal strontium ruthenate while measuring the stress-strain relationship, we reveal a huge softening of the Young's modulus at a Lifshitz transition of a two-dimensional Fermi surface and show that it is indeed driven entirely by the conduction electrons of the relevant energy band.
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Affiliation(s)
- H M L Noad
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
| | - K Ishida
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
| | - Y-S Li
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
| | - E Gati
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
| | - V Stangier
- Institut für Theorie der Kondensierten Materie, Karlsruher Institut für Technologie, 76131 Karlsruhe, Germany
| | - N Kikugawa
- National Institute for Materials Science, Tsukuba, Ibaraki 305-0003, Japan
| | - D A Sokolov
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
| | - M Nicklas
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
| | - B Kim
- Department of Physics, Kunsan National University, Gunsan 54150, Korea
- Department of Physics, Kyungpook National University, Daegu 41566, Korea
| | - I I Mazin
- Department of Physics and Astronomy, George Mason University, Fairfax, VA 22030, USA
- Quantum Science and Engineering Center, George Mason University, Fairfax, VA 22030, USA
| | - M Garst
- Institut für Theoretische Festkörperphysik, Karlsruher Institut für Technologie, 76131 Karlsruhe, Germany
- Institut für QuantenMaterialien und Technologien, Karlsruher Institut für Technologie, 76131 Karlsruhe, Germany
| | - J Schmalian
- Institut für Theorie der Kondensierten Materie, Karlsruher Institut für Technologie, 76131 Karlsruhe, Germany
- Institut für QuantenMaterialien und Technologien, Karlsruher Institut für Technologie, 76131 Karlsruhe, Germany
| | - A P Mackenzie
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
- Scottish Universities Physics Alliance, School of Physics and Astronomy, University of St Andrews, St Andrews KY16 9SS, UK
| | - C W Hicks
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
- School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK
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2
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Kim B, Khmelevskyi S, Franchini C, Mazin II. Suppressed Fluctuations as the Origin of the Static Magnetic Order in Strained Sr_{2}RuO_{4}. Phys Rev Lett 2023; 130:026702. [PMID: 36706403 DOI: 10.1103/physrevlett.130.026702] [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: 06/22/2022] [Revised: 10/04/2022] [Accepted: 12/21/2022] [Indexed: 06/18/2023]
Abstract
Combining first-principles density-functional calculations and Moriya's self-consistent renormalization theory, we explain the recently reported counterintuitive appearance of an ordered magnetic state in uniaxially strained Sr_{2}RuO_{4} beyond the Lifshitz transition. We show that strain weakens the quantum spin fluctuations, which destroy the static order, more strongly than the tendency to magnetism. A different rate of decrease of the spin fluctuations vs magnetic stabilization energy promotes the onset of a static magnetic order beyond a critical strain.
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Affiliation(s)
- Bongjae Kim
- Department of Physics, Kunsan National University, Gunsan 54150, Korea
| | - Sergii Khmelevskyi
- Center for Computational Materials Science, Institute for Applied Physics, Vienna University of Technology, Wiedner Hauptstrasse 8-10, 1040 Vienna, Austria
| | - Cesare Franchini
- University of Vienna, Faculty of Physics and Center for Computational Materials Science, Vienna A-1090, Austria
- Dipartimento di Fisica e Astronomia, Università di Bologna, 40127 Bologna, Italy
| | - I I Mazin
- Department of Physics and Astronomy, George Mason University, Fairfax, Virginia 22030, USA
- Quantum Science and Engineering Center, George Mason University, Fairfax, Virginia 22030, USA
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3
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Heinze L, Jeschke HO, Mazin II, Metavitsiadis A, Reehuis M, Feyerherm R, Hoffmann JU, Bartkowiak M, Prokhnenko O, Wolter AUB, Ding X, Zapf VS, Corvalán Moya C, Weickert F, Jaime M, Rule KC, Menzel D, Valentí R, Brenig W, Süllow S. Magnetization Process of Atacamite: A Case of Weakly Coupled S=1/2 Sawtooth Chains. Phys Rev Lett 2021; 126:207201. [PMID: 34110224 DOI: 10.1103/physrevlett.126.207201] [Citation(s) in RCA: 1] [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: 04/19/2019] [Revised: 03/25/2021] [Accepted: 03/30/2021] [Indexed: 06/12/2023]
Abstract
We present a combined experimental and theoretical study of the mineral atacamite Cu_{2}Cl(OH)_{3}. Density-functional theory yields a Hamiltonian describing anisotropic sawtooth chains with weak 3D connections. Experimentally, we fully characterize the antiferromagnetically ordered state. Magnetic order shows a complex evolution with the magnetic field, while, starting at 31.5 T, we observe a plateaulike magnetization at about M_{sat}/2. Based on complementary theoretical approaches, we show that the latter is unrelated to the known magnetization plateau of a sawtooth chain. Instead, we provide evidence that the magnetization process in atacamite is a field-driven canting of a 3D network of weakly coupled sawtooth chains that form giant moments.
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Affiliation(s)
- L Heinze
- Institut für Physik der Kondensierten Materie, Technische Universität Braunschweig, D-38106 Braunschweig, Germany
| | - H O Jeschke
- Research Institute for Interdisciplinary Science, Okayama University, Okayama 700-8530, Japan
| | - I I Mazin
- Department of Physics and Astronomy, George Mason University, Fairfax, Virginia 22030, USA
- Quantum Science and Engineering Center, George Mason University, Fairfax, Virginia 22030, USA
| | - A Metavitsiadis
- Institut für Theoretische Physik, Technische Universität Braunschweig, D-38106 Braunschweig, Germany
| | - M Reehuis
- Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, D-14109 Berlin, Germany
| | - R Feyerherm
- Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, D-14109 Berlin, Germany
| | - J-U Hoffmann
- Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, D-14109 Berlin, Germany
| | - M Bartkowiak
- Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, D-14109 Berlin, Germany
| | - O Prokhnenko
- Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, D-14109 Berlin, Germany
| | - A U B Wolter
- Institute for Solid State and Materials Research, Leibniz IFW Dresden, D-01069 Dresden, Germany
| | - X Ding
- National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - V S Zapf
- National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - C Corvalán Moya
- National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
- National Atomic Energy Commission (CNEA), Tres de Febrero University (UNTREF), National Scientific and Technical Research Council (CONICET), Argentina
| | - F Weickert
- National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - M Jaime
- National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - K C Rule
- Australian Nuclear Science and Technology Organisation, Lucas Heights, New South Wales 2234, Australia
| | - D Menzel
- Institut für Physik der Kondensierten Materie, Technische Universität Braunschweig, D-38106 Braunschweig, Germany
| | - R Valentí
- Institut für Theoretische Physik, Goethe-Universität Frankfurt, D-60438 Frankfurt am Main, Germany
| | - W Brenig
- Institut für Theoretische Physik, Technische Universität Braunschweig, D-38106 Braunschweig, Germany
| | - S Süllow
- Institut für Physik der Kondensierten Materie, Technische Universität Braunschweig, D-38106 Braunschweig, Germany
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4
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Ghimire NJ, Dally RL, Poudel L, Jones DC, Michel D, Magar NT, Bleuel M, McGuire MA, Jiang JS, Mitchell JF, Lynn JW, Mazin II. Competing magnetic phases and fluctuation-driven scalar spin chirality in the kagome metal YMn 6Sn 6. Sci Adv 2020; 6:6/51/eabe2680. [PMID: 33355145 DOI: 10.1126/sciadv.abe2680] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2020] [Accepted: 11/02/2020] [Indexed: 05/25/2023]
Abstract
Identification, understanding, and manipulation of novel magnetic textures are essential for the discovery of new quantum materials for future spin-based electronic devices. In particular, materials that manifest a large response to external stimuli such as a magnetic field are subject to intense investigation. Here, we study the kagome-net magnet YMn6Sn6 by magnetometry, transport, and neutron diffraction measurements combined with first-principles calculations. We identify a number of nontrivial magnetic phases, explain their microscopic nature, and demonstrate that one of them hosts a large topological Hall effect (THE). We propose a previously unidentified fluctuation-driven mechanism, which leads to the THE at elevated temperatures. This interesting physics comes from parametrically frustrated interplanar exchange interactions that trigger strong magnetic fluctuations. Our results pave a path to chiral spin textures, promising for novel spintronics.
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Affiliation(s)
- Nirmal J Ghimire
- Department of Physics and Astronomy, George Mason University, Fairfax, VA 22030, USA.
- Quantum Science and Engineering Center, George Mason University, Fairfax, VA 22030, USA
| | - Rebecca L Dally
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - L Poudel
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
- Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742, USA
| | - D C Jones
- Department of Physics and Astronomy, George Mason University, Fairfax, VA 22030, USA
- Quantum Science and Engineering Center, George Mason University, Fairfax, VA 22030, USA
| | - D Michel
- Department of Physics and Astronomy, George Mason University, Fairfax, VA 22030, USA
- Quantum Science and Engineering Center, George Mason University, Fairfax, VA 22030, USA
| | - N Thapa Magar
- Department of Physics and Astronomy, George Mason University, Fairfax, VA 22030, USA
| | - M Bleuel
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
- Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742, USA
| | - Michael A McGuire
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
| | - J S Jiang
- Materials Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439, USA
| | - J F Mitchell
- Materials Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439, USA
| | - Jeffrey W Lynn
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - I I Mazin
- Department of Physics and Astronomy, George Mason University, Fairfax, VA 22030, USA
- Quantum Science and Engineering Center, George Mason University, Fairfax, VA 22030, USA
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5
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Petsch AN, Zhu M, Enderle M, Mao ZQ, Maeno Y, Mazin II, Hayden SM. Reduction of the Spin Susceptibility in the Superconducting State of Sr_{2}RuO_{4} Observed by Polarized Neutron Scattering. Phys Rev Lett 2020; 125:217004. [PMID: 33275021 DOI: 10.1103/physrevlett.125.217004] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/07/2020] [Revised: 07/01/2020] [Accepted: 10/14/2020] [Indexed: 06/12/2023]
Abstract
Recent observations [A. Pustogow et al., Nature (London) 574, 72 (2019).NATUAS0028-083610.1038/s41586-019-1596-2] of a drop of the ^{17}O nuclear magnetic resonance (NMR) Knight shift in the superconducting state of Sr_{2}RuO_{4} challenged the popular picture of a chiral odd-parity paired state in this compound. Here we use polarized neutron scattering (PNS) to show that there is a 34±6% drop in the magnetic susceptibility at the Ru site below the superconducting transition temperature. We measure at lower fields H∼1/3H_{c2} than a previous PNS study allowing the suppression to be observed. The PNS measurements show a smaller susceptibility suppression than NMR measurements performed at similar field and temperature. Our results rule out the chiral odd-parity d=z[over ^](k_{x}±ik_{y}) state and are consistent with several recent proposals for the order parameter including even-parity B_{1g} and odd-parity helical states.
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Affiliation(s)
- A N Petsch
- H.H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, United Kingdom
| | - M Zhu
- H.H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, United Kingdom
| | | | - Z Q Mao
- Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
- Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Y Maeno
- Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | - I I Mazin
- Department of Physics and Astronomy, George Mason University and Quantum Science and Engineering Center, Fairfax, Virginia 22030, USA
| | - S M Hayden
- H.H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, United Kingdom
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6
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Mazin II, Shimizu M, Takemori N, Jeschke HO. Novel Fe-Based Superconductor LaFe_{2}As_{2} in Comparison with Traditional Pnictides. Phys Rev Lett 2019; 123:267001. [PMID: 31951452 DOI: 10.1103/physrevlett.123.267001] [Citation(s) in RCA: 1] [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: 05/15/2019] [Indexed: 06/10/2023]
Abstract
The recently discovered Fe-based superconductor (FeBS) LaFe_{2}As_{2} seems to break away from an established pattern that doping an FeBS beyond 0.2e/Fe destroys superconductivity. LaFe_{2}As_{2} has an apparent doping of 0.5e, yet superconducts at 12.1 K. Its Fermi surface bears no visual resemblance with the canonical FeBS fermiology. It also exhibits two phases, none magnetic and only one superconducting. We show that the difference between them nonetheless has a magnetic origin, the one featuring disordered moments, and the other locally nonmagnetic. We find that La there assumes an unusual valence of +2.6 to +2.7, so that the effective doping is reduced to 0.30-0.35e. A closer look reveals the same key elements: hole Fermi surfaces near Γ-Z and electron ones near the X-P lines, with the corresponding peak in susceptibility, and a strong tendency to stripe magnetism. The physics of LaFe_{2}As_{2} is thus more similar to the FeBS paradigm than hitherto appreciated.
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Affiliation(s)
- I I Mazin
- Code 6393, Naval Research Laboratory, Washington, DC 20375, USA
| | - Makoto Shimizu
- Department of Physics, Okayama University, Okayama 700-8530, Japan
| | - Nayuta Takemori
- Research Institute for Interdisciplinary Science, Okayama University, Okayama 700-8530, Japan
| | - Harald O Jeschke
- Research Institute for Interdisciplinary Science, Okayama University, Okayama 700-8530, Japan
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7
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Mazin II. Why have band theorists been so successful in explaining and predicting novel superconductors? J Phys Condens Matter 2019; 31:174001. [PMID: 30695752 DOI: 10.1088/1361-648x/ab02ad] [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: 06/09/2023]
Abstract
In this contribution to the J. Phys.: Condens. Matter memorial issue in honor of Sandro Massidda I reflect on a phenomenon Sandro had been a part of. While theoretical condensed matter physicists have made, over the years, exciting and most elegant contributions to the theory of superconductivity (which, in and by itself, is one of the most beautiful constructs in theoretical physics), some of them of utmost importance, they have had less success in predicting and explaining superconducting states and mechanisms in specific materials. More down-to-earth computational materials scientists, who often go by the moniker 'band theorists', have been much more successful in applying (usually other people's) ideas in such circumstances. In this essay I give some examples, largely drawn from my own experience, and speculate on their meaning.
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Affiliation(s)
- I I Mazin
- Code 6393, Naval Research Laboratory, Washington, DC 20375, United States of America
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Steffens P, Sidis Y, Kulda J, Mao ZQ, Maeno Y, Mazin II, Braden M. Spin Fluctuations in Sr_{2}RuO_{4} from Polarized Neutron Scattering: Implications for Superconductivity. Phys Rev Lett 2019; 122:047004. [PMID: 30768293 DOI: 10.1103/physrevlett.122.047004] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/09/2018] [Indexed: 06/09/2023]
Abstract
Triplet pairing in Sr_{2}RuO_{4} was initially suggested based on the hypothesis of strong ferromagnetic spin fluctuations. Using polarized inelastic neutron scattering, we accurately determine the full spectrum of spin fluctuations in Sr_{2}RuO_{4}. Besides the well-studied incommensurate magnetic fluctuations, we do find a sizable quasiferromagnetic signal, quantitatively consistent with all macroscopic and microscopic probes. We use this result to address the possibility of magnetically driven triplet superconductivity in Sr_{2}RuO_{4}. We conclude that, even though the quasiferromagnetic signal is stronger and sharper than previously anticipated, spin fluctuations alone are not enough to generate a triplet state strengthening the need for additional interactions or an alternative pairing scenario.
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Affiliation(s)
- P Steffens
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany
- Institut Laue Langevin, 71 avenue des Martyrs, 38000 Grenoble, France
| | - Y Sidis
- Laboratoire Léon Brillouin, C.E.A./C.N.R.S., F-91191 Gif-sur-Yvette CEDEX, France
| | - J Kulda
- Institut Laue Langevin, 71 avenue des Martyrs, 38000 Grenoble, France
| | - Z Q Mao
- Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
- Department of Physics, Tulane University, New Orleans, Louisiana 70118, USA
- Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Y Maeno
- Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | - I I Mazin
- Code 6393, Naval Research Laboratory, Washington, DC 20375, USA
| | - M Braden
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany
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Lechermann F, Bernstein N, Mazin II, Valentí R. Uncovering the Mechanism of the Impurity-Selective Mott Transition in Paramagnetic V_{2}O_{3}. Phys Rev Lett 2018; 121:106401. [PMID: 30240239 DOI: 10.1103/physrevlett.121.106401] [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: 01/26/2018] [Indexed: 06/08/2023]
Abstract
While the phase diagrams of the one- and multiorbital Hubbard model have been well studied, the physics of real Mott insulators is often much richer, material dependent, and poorly understood. In the prototype Mott insulator V_{2}O_{3}, chemical pressure was initially believed to explain why the paramagnetic-metal to antiferromagnetic-insulator transition temperature is lowered by Ti doping while Cr doping strengthens correlations, eventually rendering the high-temperature phase paramagnetic insulating. However, this scenario has been recently shown both experimentally and theoretically to be untenable. Based on full structural optimization, we demonstrate via the charge self-consistent combination of density functional theory and dynamical mean-field theory that changes in the V_{2}O_{3} phase diagram are driven by defect-induced local symmetry breakings resulting from dramatically different couplings of Cr and Ti dopants to the host system. This finding emphasizes the high sensitivity of the Mott metal-insulator transition to the local environment and the importance of accurately accounting for the one-electron Hamiltonian, since correlations crucially respond to it.
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Affiliation(s)
- Frank Lechermann
- I. Institut für Theoretische Physik, Universität Hamburg, Jungiusstraße 9, D-20355 Hamburg, Germany
| | - Noam Bernstein
- Code 6393, Naval Research Laboratory, Washington, DC 20375, USA
| | - I I Mazin
- Code 6393, Naval Research Laboratory, Washington, DC 20375, USA
| | - Roser Valentí
- Institut für Theoretische Physik, Goethe-Universität Frankfurt, Max-von-Laue-Straße 1, 60438 Frankfurt am Main, Germany
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10
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Guterding D, Jeschke HO, Mazin II, Glasbrenner JK, Bascones E, Valentí R. Nontrivial Role of Interlayer Cation States in Iron-Based Superconductors. Phys Rev Lett 2017; 118:017204. [PMID: 28106450 DOI: 10.1103/physrevlett.118.017204] [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: 10/27/2016] [Indexed: 06/06/2023]
Abstract
Unconventional superconductivity in iron pnictides and chalcogenides has been suggested to be controlled by the interplay of low-energy antiferromagnetic spin fluctuations and the particular topology of the Fermi surface in these materials. Based on this premise, one would also expect the large class of isostructural and isoelectronic iron germanide compounds to be good superconductors. As a matter of fact, they, however, superconduct at very low temperatures or not at all. In this work we establish that superconductivity in iron germanides is suppressed by strong ferromagnetic tendencies, which surprisingly do not originate from changes in bond angles or bond distances with respect to iron pnictides and chalcogenides, but are due to changes in the electronic structure in a wide range of energies happening upon substitution of atom species (As by Ge and the corresponding spacer cations). Our results indicate that superconductivity in iron-based materials may not always be fully understood based on d or d-p model Hamiltonians only.
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Affiliation(s)
- Daniel Guterding
- Institut für Theoretische Physik, Goethe-Universität Frankfurt, Max-von-Laue-Straße 1, 60438 Frankfurt am Main, Germany
| | - Harald O Jeschke
- Institut für Theoretische Physik, Goethe-Universität Frankfurt, Max-von-Laue-Straße 1, 60438 Frankfurt am Main, Germany
| | - I I Mazin
- Code 6393, Naval Research Laboratory, Washington, District of Columbia 20375, USA
| | - J K Glasbrenner
- National Research Council/Code 6393, Naval Research Laboratory, Washington, District of Columbia 20375, USA
| | - E Bascones
- Instituto de Ciencia de Materiales de Madrid, ICMM-CSIC, Cantoblanco, 28049 Madrid, Spain
| | - Roser Valentí
- Institut für Theoretische Physik, Goethe-Universität Frankfurt, Max-von-Laue-Straße 1, 60438 Frankfurt am Main, Germany
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11
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Ortenzi L, Gretarsson H, Kasahara S, Matsuda Y, Shibauchi T, Finkelstein KD, Wu W, Julian SR, Kim YJ, Mazin II, Boeri L. Structural origin of the anomalous temperature dependence of the local magnetic moments in the CaFe2As2 family of materials. Phys Rev Lett 2015; 114:047001. [PMID: 25679903 DOI: 10.1103/physrevlett.114.047001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2014] [Indexed: 06/04/2023]
Abstract
We report a combination of Fe Kβ x-ray emission spectroscopy and density functional reduced Stoner theory calculations to investigate the correlation between structural and magnetic degrees of freedom in CaFe2(As1-xPx)2. The puzzling temperature behavior of the local moment found in rare earth-doped CaFe2As2 [H. Gretarsson et al., Phys. Rev. Lett. 110, 047003 (2013)] is also observed in CaFe2(As1-xPx)2. We explain this phenomenon based on first-principles calculations with scaled magnetic interaction. One scaling parameter is sufficient to describe quantitatively the magnetic moments in both CaFe2(As1-xPx)2 (x=0.055) and Ca0.78La0.22Fe2As2 at all temperatures. The anomalous growth of the local moments with increasing temperature can be understood from the observed large thermal expansion of the c-axis lattice parameter combined with strong magnetoelastic coupling. These effects originate from the strong tendency to form As-As dimers across the Ca layer in the CaFe2As2 family of materials. Our results emphasize the dual local-itinerant character of magnetism in Fe pnictides.
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Affiliation(s)
- L Ortenzi
- Institute for Complex Systems (ISC-CNR), c/o Dipartimento di Fisica, Università "La Sapienza", Piazzale Aldo Moro, n. 5, 00185 Rome, Italy and Max-Planck-Institut für Festkörperforschung, Heisenbergstraβe 1, D-70569 Stuttgart, Germany
| | - H Gretarsson
- Max-Planck-Institut für Festkörperforschung, Heisenbergstraβe 1, D-70569 Stuttgart, Germany and Department of Physics, University of Toronto, 60 Saint George Street, Toronto, Ontario M5S 1A7, Canada
| | - S Kasahara
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - Y Matsuda
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - T Shibauchi
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan and Department of Advanced Materials Science, University of Tokyo, Kashiwa 277-8561, Japan
| | - K D Finkelstein
- Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York 14853, USA
| | - W Wu
- Department of Physics, University of Toronto, 60 Saint George Street, Toronto, Ontario M5S 1A7, Canada
| | - S R Julian
- Department of Physics, University of Toronto, 60 Saint George Street, Toronto, Ontario M5S 1A7, Canada
| | - Young-June Kim
- Department of Physics, University of Toronto, 60 Saint George Street, Toronto, Ontario M5S 1A7, Canada
| | - I I Mazin
- Code 6390, Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375, USA
| | - L Boeri
- Institute for Theoretical and Computational Physics, TU Graz, Petersgasse 16, 8010 Graz, Austria
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Mazin II, Jeschke HO, Lechermann F, Lee H, Fink M, Thomale R, Valentí R. Theoretical prediction of a strongly correlated Dirac metal. Nat Commun 2014; 5:4261. [PMID: 24980208 DOI: 10.1038/ncomms5261] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2014] [Accepted: 05/30/2014] [Indexed: 11/09/2022] Open
Abstract
Recently, the most intensely studied objects in the electronic theory of solids have been strongly correlated systems and graphene. However, the fact that the Dirac bands in graphene are made up of sp(2) electrons, which are subject to neither strong Hubbard repulsion U nor strong Hund's rule coupling J, creates certain limitations in terms of novel, interaction-induced physics that could be derived from Dirac points. Here we propose GaCu3(OH)6Cl2 (Ga-substituted herbertsmithite) as a correlated Dirac-Kagome metal combining Dirac electrons, strong interactions and frustrated magnetic interactions. Using density functional theory, we calculate its crystallographic and electronic properties, and observe that it has symmetry-protected Dirac points at the Fermi level. Its many-body physics is diverse, with possible charge, magnetic and superconducting instabilities. Through a combination of various many-body methods we study possible symmetry-lowering phase transitions such as Mott-Hubbard, charge or magnetic ordering, and unconventional superconductivity, which in this compound assumes an f-wave symmetry.
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Affiliation(s)
- I I Mazin
- Code 6393, Naval Research Laboratory, Washington, District of Columbia 20375, USA
| | - Harald O Jeschke
- Institut für Theoretische Physik, Goethe-Universität Frankfurt, Max-von-Laue-Strasse 1, 60438 Frankfurt am Main, Germany
| | - Frank Lechermann
- I. Institut für Theoretische Physik, Universität Hamburg, D-20355 Hamburg, Germany
| | - Hunpyo Lee
- Institut für Theoretische Physik, Goethe-Universität Frankfurt, Max-von-Laue-Strasse 1, 60438 Frankfurt am Main, Germany
| | - Mario Fink
- Institut für Theoretische Physik I, Universität Würzburg, am Hubland, 97074 Würzburg, Germany
| | - Ronny Thomale
- Institut für Theoretische Physik I, Universität Würzburg, am Hubland, 97074 Würzburg, Germany
| | - Roser Valentí
- Institut für Theoretische Physik, Goethe-Universität Frankfurt, Max-von-Laue-Strasse 1, 60438 Frankfurt am Main, Germany
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13
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Eschrig M, Golubov AA, Mazin II, Nadgorny B, Tanaka Y, Valls OT, Zutić I. Comment on "Unified formalism of Andreev reflection at a ferromagnet/superconductor interface". Phys Rev Lett 2013; 111:139703. [PMID: 24116824 DOI: 10.1103/physrevlett.111.139703] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2013] [Indexed: 06/02/2023]
Affiliation(s)
- M Eschrig
- Department of Physics, Royal Holloway, University of London, Egham, Surrey TW20 0EX, United Kingdom
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14
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Blomberg EC, Tanatar MA, Fernandes RM, Mazin II, Shen B, Wen HH, Johannes MD, Schmalian J, Prozorov R. Sign-reversal of the in-plane resistivity anisotropy in hole-doped iron pnictides. Nat Commun 2013; 4:1914. [DOI: 10.1038/ncomms2933] [Citation(s) in RCA: 95] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2012] [Accepted: 04/26/2013] [Indexed: 11/09/2022] Open
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15
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Abstract
Contrary to previous studies that classify Na(2)IrO(3) as a realization of the Heisenberg-Kitaev model with a dominant spin-orbit coupling, we show that this system represents a highly unusual case in which the electronic structure is dominated by the formation of quasimolecular orbitals (QMOs), with substantial quenching of the orbital moments. The QMOs consist of six atomic orbitals on an Ir hexagon, but each Ir atom belongs to three different QMOs. The concept of such QMOs in solids invokes very different physics compared to the models considered previously. Employing density functional theory calculations and model considerations we find that both the insulating behavior and the experimentally observed zigzag antiferromagnetism in Na(2)IrO(3) naturally follow from the QMO model.
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Affiliation(s)
- I I Mazin
- Code 6393, Naval Research Laboratory, Washington, DC 20375, USA
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16
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Choi SK, Coldea R, Kolmogorov AN, Lancaster T, Mazin II, Blundell SJ, Radaelli PG, Singh Y, Gegenwart P, Choi KR, Cheong SW, Baker PJ, Stock C, Taylor J. Spin waves and revised crystal structure of honeycomb iridate Na2IrO3. Phys Rev Lett 2012; 108:127204. [PMID: 22540621 DOI: 10.1103/physrevlett.108.127204] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2011] [Indexed: 05/31/2023]
Abstract
We report inelastic neutron scattering measurements on Na2IrO3, a candidate for the Kitaev spin model on the honeycomb lattice. We observe spin-wave excitations below 5 meV with a dispersion that can be accounted for by including substantial further-neighbor exchanges that stabilize zigzag magnetic order. The onset of long-range magnetic order below T(N)=15.3 K is confirmed via the observation of oscillations in zero-field muon-spin rotation experiments. Combining single-crystal diffraction and density functional calculations we propose a revised crystal structure model with significant departures from the ideal 90° Ir-O-Ir bonds required for dominant Kitaev exchange.
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Affiliation(s)
- S K Choi
- Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
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17
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Putzke C, Coldea AI, Guillamón I, Vignolles D, McCollam A, Leboeuf D, Watson MD, Mazin II, Kasahara S, Terashima T, Shibauchi T, Matsuda Y, Carrington A. de Haas-van Alphen study of the Fermi surfaces of superconducting LiFeP and LiFeAs. Phys Rev Lett 2012; 108:047002. [PMID: 22400881 DOI: 10.1103/physrevlett.108.047002] [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: 07/25/2011] [Indexed: 05/31/2023]
Abstract
We report a de Haas-van Alphen oscillation study of the 111 iron pnictide superconductors LiFeAs with T(c) ≈ 18 K and LiFeP with T(c) ≈ 5 K. We find that for both compounds the Fermi surface topology is in good agreement with density functional band-structure calculations and has almost nested electron and hole bands. The effective masses generally show significant enhancement, up to ~3 for LiFeP and ~5 for LiFeAs. However, one hole Fermi surface in LiFeP shows a very small enhancement, as compared with its other sheets. This difference probably results from k-dependent coupling to spin fluctuations and may be the origin of the different nodal and nodeless superconducting gap structures in LiFeP and LiFeAs, respectively.
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Affiliation(s)
- C Putzke
- HH Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, United Kingdom
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18
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Pascut GL, Coldea R, Radaelli PG, Bombardi A, Beutier G, Mazin II, Johannes MD, Jansen M. Direct observation of charge order in triangular metallic AgNiO2 by single-crystal resonant X-ray scattering. Phys Rev Lett 2011; 106:157206. [PMID: 21568611 DOI: 10.1103/physrevlett.106.157206] [Citation(s) in RCA: 4] [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: 09/10/2010] [Indexed: 05/30/2023]
Abstract
We report resonant x-ray scattering measurements on a single crystal of the orbitally degenerate triangular metallic antiferromagnet 2H-AgNiO2 to probe the spontaneous transition to a triple-cell superstructure at temperatures below T(S)=365 K. We observe a strong resonant enhancement of the supercell reflections through the Ni K edge. The empirically extracted K-edge shift between the crystallographically distinct Ni sites of 2.5(3) eV is much larger than the value expected from the shift in final states, and implies a core-level shift of ∼1 eV, thus providing direct evidence for the onset of spontaneous honeycomb charge order in the triangular Ni layers. We also provide band-structure calculations that explain quantitatively the observed edge shifts in terms of changes in the Ni electronic energy levels due to charge order and hybridization with the surrounding oxygens.
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Affiliation(s)
- G L Pascut
- Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
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19
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Abstract
AbstractThe use of first principles methods based on density functional theory to investigate novel thermoelectric materials is illustrated for several empty and filled skutterudite compounds, including CoSb3, COP3, La(Fe,Co)4Sb12 and La(Fe,Co)P12. Band structures and their relationship to transport properties especially as regards optimization of thermoelectric properties is discussed. Phonon models constructed from calculations and existing experimental data for CoSb3 are presented. These have been extended to the filled skutterudites, particularly LaFe4Sb12 using additional first principles calculations to fix the La related parameters in the model. This model allows an interpretation of neutron scattering data as well as an understanding of the low frequency phonon modes that transport heat in these compounds.
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Cohen RE, Fei Y, Downs R, Mazin II, Isaak DG. Magnetic Collapse and the Behavior of Transition Metal Oxides: FeO at High Pressures. ACTA ACUST UNITED AC 2011. [DOI: 10.1557/proc-499-27] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
ABSTRACTLinearized augmented plane wave (LAPW) results are presented for FeO at high pressures using the Generalized Gradient Approximation (GGA) to study the high-spin low-spin transition previously predicted by LAPW with the Local Density Approximation (LDA) and Linear Muffin Tin Orbital (LMTO-ASA) methods within the GGA. We find a first-order transition at a pressure of about 105 GPa for the cubic lattice, consistent with earlier LAPW results, but much lower than obtained with the LMTO. The results are generally consistent with recent Mössbauer experiments that show a transition at about 100 GPa. We also discuss the origin of the transition, and show that it is not due to electrostatic crystal-field effects, but is rather due to hybridization and band widening with pressure. Examination of experimental data and computations suggest that the high pressure hexagonal phase of FeO is likely a polytype between the B8 NiAs and anti-B8 AsNi structures. The former is predicted to be an antiferromagnetic metal, and the latter an antiferromagnetic insulator. Implications for geophysics are discussed.
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21
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Golubov AA, Brinkman A, Tanaka Y, Mazin II, Dolgov OV. Andreev spectra and subgap bound states in multiband superconductors. Phys Rev Lett 2009; 103:077003. [PMID: 19792677 DOI: 10.1103/physrevlett.103.077003] [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: 12/29/2008] [Indexed: 05/28/2023]
Abstract
A theory of Andreev conductance is formulated for junctions involving normal metals (N) and multiband superconductors (S) and applied to the case of superconductors with nodeless extended s(+/-)-wave order parameter symmetry, as possibly realized in the recently discovered ferropnictides. We find qualitative differences from tunneling into s-wave or d-wave superconductors that may help to identify such a state. First, interband interference leads to a suppression of Andreev reflection in the case of a highly transparent N/S interface and to a current deficit in the tunneling regime. Second, surface bound states may appear, both at zero and at nonzero energies.
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Affiliation(s)
- A A Golubov
- MESA+ Institute for Nanotechnology, University of Twente, 7500 AE Enschede, The Netherlands
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22
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Parker D, Mazin II. Possible phase-sensitive tests of pairing symmetry in pnictide superconductors. Phys Rev Lett 2009; 102:227007. [PMID: 19658896 DOI: 10.1103/physrevlett.102.227007] [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: 12/23/2008] [Indexed: 05/28/2023]
Abstract
The discovery of the new class of pnictide superconductors has engendered a controversy about their pairing symmetry, with proposals ranging from an extended s wave or "s_{+/-}" symmetry to nodal or nodeless d-wave symmetry to still more exotic order parameters such as p wave. In this Letter, building on the earlier, similar work performed for the cuprates, we propose several phase-sensitive Josephson interferometry experiments, each of which may allow resolution of the issue.
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Affiliation(s)
- D Parker
- Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, D.C., 20375, USA
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23
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Pillay D, Johannes MD, Mazin II. Electronic structure of the NaxCoO2 surface. Phys Rev Lett 2008; 101:246808. [PMID: 19113650 DOI: 10.1103/physrevlett.101.246808] [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: 05/29/2008] [Indexed: 05/27/2023]
Abstract
The idea that surface effects may play an important role in suppressing eg' Fermi surface pockets on NaxCoO2 (0.333 < or = x < or = 0.75) has been frequently proposed to explain the discrepancy between local-density approximation calculations which find eg' hole pockets present and Angle resolved photoemission spectra (ARPES) experiments, which do not observe the hole pockets. Since ARPES is a surface sensitive technique, it is important to investigate the effects that surface formation will have on the electronic structure. We show that a combination of surface formation and contamination effects could resolve the ongoing controversy between ARPES experiments and theory.
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Affiliation(s)
- D Pillay
- Code 6393, Naval Research Laboratory, Washington, DC 20375, USA
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24
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Mazin II, Johannes MD, Sawatzky GA. Comment on "Low-lying States and hidden kinematic collective charge instabilities in parent cobaltate superconductors". Phys Rev Lett 2008; 101:089703-089704. [PMID: 18764667 DOI: 10.1103/physrevlett.101.089703] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2006] [Indexed: 05/26/2023]
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25
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Mazin II, Singh DJ, Johannes MD, Du MH. Unconventional superconductivity with a sign reversal in the order parameter of LaFeAsO1-xFx. Phys Rev Lett 2008; 101:057003. [PMID: 18764420 DOI: 10.1103/physrevlett.101.057003] [Citation(s) in RCA: 120] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2008] [Indexed: 05/15/2023]
Abstract
We argue that the newly discovered superconductivity in a nearly magnetic, Fe-based layered compound is unconventional and mediated by antiferromagnetic spin fluctuations, though different from the usual superexchange and specific to this compound. This resulting state is an example of extended s-wave pairing with a sign reversal of the order parameter between different Fermi surface sheets. The main role of doping in this scenario is to lower the density of states and suppress the pair-breaking ferromagnetic fluctuations.
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Affiliation(s)
- I I Mazin
- Code 6393, Naval Research Laboratory, Washington, D.C. 20375, USA
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26
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van Mechelen JLM, van der Marel D, Grimaldi C, Kuzmenko AB, Armitage NP, Reyren N, Hagemann H, Mazin II. Electron-phonon interaction and charge carrier mass enhancement in SrTiO3. Phys Rev Lett 2008; 100:226403. [PMID: 18643435 DOI: 10.1103/physrevlett.100.226403] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2007] [Revised: 04/15/2008] [Indexed: 05/26/2023]
Abstract
We report a comprehensive THz, infrared and optical study of Nb-doped SrTiO3 as well as dc conductivity and Hall effect measurements. Our THz spectra at 7 K show the presence of an unusually narrow (<2 meV) Drude peak. For all carrier concentrations the Drude spectral weight shows a factor of three mass enhancement relative to the effective mass in the local density approximation, whereas the spectral weight contained in the incoherent midinfrared response indicates that the mass enhancement is at least a factor two. We find no evidence of a particularly large electron-phonon coupling that would result in small polaron formation.
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Affiliation(s)
- J L M van Mechelen
- Département de Physique de la Matière Condensée, Université de Genève, Genève, Switzerland
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27
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28
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Wawrzyńska E, Coldea R, Wheeler EM, Mazin II, Johannes MD, Sörgel T, Jansen M, Ibberson RM, Radaelli PG. Orbital degeneracy removed by charge order in triangular antiferromagnet AgNiO2. Phys Rev Lett 2007; 99:157204. [PMID: 17995209 DOI: 10.1103/physrevlett.99.157204] [Citation(s) in RCA: 4] [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: 05/04/2007] [Indexed: 05/25/2023]
Abstract
We report a high-resolution neutron diffraction study on the orbitally degenerate spin-1/2 hexagonal metallic antiferromagnet AgNiO2. A structural transition to a tripled unit cell with expanded and contracted NiO6 octahedra indicates sqrt[3]xsqrt[3] charge order on the Ni triangular lattice. This suggests charge order as a possible mechanism of lifting the orbital degeneracy in the presence of charge fluctuations, as an alternative to the more usual Jahn-Teller distortions. A novel magnetic ground state is observed at low temperatures with the electron-rich S=1 Ni sites arranged in alternating ferromagnetic rows on a triangular lattice, surrounded by a honeycomb network of nonmagnetic and metallic Ni ions. We also report first-principles band-structure calculations that explain microscopically the origin of these phenomena.
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Affiliation(s)
- E Wawrzyńska
- H.H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, United Kingdom
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29
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Dolgov OV, Mazin II, Golubov AA, Savrasov SY, Maksimov EG. Critical temperature and enhanced isotope effect in the presence of paramagnons in phonon-mediated superconductors. Phys Rev Lett 2005; 95:257003. [PMID: 16384497 DOI: 10.1103/physrevlett.95.257003] [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: 06/14/2005] [Indexed: 05/05/2023]
Abstract
We reconsider the long-standing problem of the effect of spin fluctuations on the critical temperature and isotope effect in a phonon-mediated superconductor. Although the general physics of the interplay between phonons and paramagnons has been rather well understood, the existing approximate formulas fail to describe the correct behavior of Tc for general phonon and paramagnon spectra. Using a controllable approximation, we derive an analytical formula for Tc which agrees well with exact numerical solutions of the Eliashberg equations for a broad range of parameters. Based on both numerical and analytical results, we predict a strong enhancement of the isotope effect when the frequencies of spin fluctuation and phonons are of the same order. This effect may have important consequences for near-magnetic superconductors such as MgCNi3.
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Affiliation(s)
- O V Dolgov
- Max-Planck-Institut für Festkörperphysik, Heisenbergstrasse 1, 70569 Stuttgart, Germany
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30
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Abstract
Recently discovered superconductivity in YbC6 and CaC6, at temperatures substantially higher than previously known for intercalated graphites, raises several new questions. (1) Is the mechanism considerably different from that of previously known intercalated graphites? (2) If superconductivity is conventional, what are the relevant phonons? (3) Given the extreme similarity between YbC6 and CaC6, why are their critical temperatures so different? We address these questions on the basis of first-principles calculations and conclude that coupling with intercalant phonons is likely to be the main force for superconductivity in YbC6 and CaC6, but not in alkaline-intercalated compounds, and explain the difference in T(c) by the "isotope effect" due to the difference in Yb and Ca atomic masses.
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Affiliation(s)
- I I Mazin
- Center for Computational Materials Science, Naval Research Laboratory, Washington, DC 20375, USA
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31
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Johannes MD, Mazin II, Singh DJ, Papaconstantopoulos DA. Nesting, spin fluctuations, and odd-gap superconductivity in NaxCoO2.yH2O. Phys Rev Lett 2004; 93:097005. [PMID: 15447132 DOI: 10.1103/physrevlett.93.097005] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2004] [Indexed: 05/24/2023]
Abstract
We calculated the one-electron susceptibility of hydrated NaxCoO2 and find strong nesting, involving about 70% of all electrons at the Fermi level and nearly commensurate with a 2 x 2 superstructure. This nesting creates a tendency to a charge density wave compatible with the charge order often seen at x approximately 0.5 and usually ascribed to electrostatic repulsion of Na ions. In the spin channel, it leads to strong spin fluctuations, which should be important for superconductivity. The state most compatible with this nesting structure is an odd-gap triplet s-wave state.
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Affiliation(s)
- M D Johannes
- Code 6391, Naval Research Laboratory, Washington, DC 20375, USA
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32
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Aguayo A, Mazin II, Singh DJ. Why Ni3Al is an itinerant ferromagnet but Ni3Ga is not. Phys Rev Lett 2004; 92:147201. [PMID: 15089568 DOI: 10.1103/physrevlett.92.147201] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2003] [Revised: 10/31/2003] [Indexed: 05/24/2023]
Abstract
Ni3Al and Ni3Ga are closely related materials on opposite sides of a ferromagnetic quantum critical point. The Stoner factor of Ni is virtually the same in both compounds and the density of states is larger in Ni3Ga. Thus in Stoner theory it should be more magnetic, and in local-density approximation (LDA) calculations it is. However, experimentally it is a paramagnet, while Ni3Al is an itinerant ferromagnet. We show that critical spin fluctuations are stronger in Ni3Ga, due to weaker q dependence of the susceptibility, and this effect is enough to reverse the trend. The approach combines LDA calculations with Landau theory and the fluctuation-dissipation theorem using the same momentum cutoff for both compounds. The calculations provide evidence for strong, beyond LDA, spin fluctuations associated with the critical point in both materials, but stronger in Ni3Ga than in Ni3Al.
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Affiliation(s)
- A Aguayo
- Center for Computational Materials Science, Naval Research Laboratory, Washington, D.C. 20375, USA
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33
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Maksimov EG, Kortus J, Dolgov OV, Mazin II. Reflectance measurements and superconductivity in MgB2. Phys Rev Lett 2002; 89:129703. [PMID: 12225131 DOI: 10.1103/physrevlett.89.129703] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/13/2001] [Indexed: 05/23/2023]
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34
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Mazin II, Andersen OK, Jepsen O, Dolgov OV, Kortus J, Golubov AA, Kuz'menko AB, Van Der Marel D. Superconductivity in MgB2: clean or dirty? Phys Rev Lett 2002; 89:107002. [PMID: 12225216 DOI: 10.1103/physrevlett.89.107002] [Citation(s) in RCA: 18] [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: 04/01/2002] [Indexed: 05/23/2023]
Abstract
A large number of experimental facts and theoretical arguments favor a two-gap model for superconductivity in MgB2. However, this model predicts strong suppression of the critical temperature by interband impurity scattering and, presumably, a strong correlation between the critical temperature and the residual resistivity. No such correlation has been observed. We argue that this fact can be understood if the band disparity of the electronic structure is taken into account, not only in the superconducting state, but also in normal transport.
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Affiliation(s)
- I I Mazin
- Center for Computational Materials Science, Naval Research Laboratory, Washington, DC 20375-5000, USA
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35
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Abstract
It has long been suspected that spin fluctuations in ZrZn2 may lead to a triplet superconductivity. We point out another possibility, an inhomogeneous singlet (Fulde-Ferrell) state. We calculated the electronic structure, as well as the zone center phonons and their coupling with electrons. We find that the exchange splitting is nonuniform and the Fermi surface exhibits substantial nesting. Both factors favor a Fulde-Ferrell state at parts of the Fermi surface. We find a substantial coupling of Zr rattling modes with electrons, which can provide the necessary pairing in the s-channel.
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Affiliation(s)
- D J Singh
- Code 6390, Naval Research Laboratory, Washington, D.C. 20375, USA
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36
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Liu AY, Mazin II, Kortus J. Beyond Eliashberg superconductivity in MgB2: anharmonicity, two-phonon scattering, and multiple gaps. Phys Rev Lett 2001; 87:087005. [PMID: 11497975 DOI: 10.1103/physrevlett.87.087005] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/2001] [Indexed: 05/23/2023]
Abstract
Density-functional calculations of the phonon spectrum and electron-phonon coupling in MgB (2) are presented. The E(2g) phonons, which involve in-plane B displacements, couple strongly to the p(x,y) electronic bands. The isotropic electron-phonon coupling constant is calculated to be about 0.8. Allowing for different order parameters in different bands, the superconducting lambda in the clean limit is calculated to be significantly larger. The E(2g) phonons are strongly anharmonic, and the nonlinear contribution to the coupling between the E(2g) modes and the p(x,y) bands is significant.
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Affiliation(s)
- A Y Liu
- Department of Physics, Georgetown University, Washington, DC 20057, USA
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37
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Kortus J, Mazin II, Belashchenko KD, Antropov VP, Boyer LL. Superconductivity of metallic boron in MgB2. Phys Rev Lett 2001; 86:4656-4659. [PMID: 11384307 DOI: 10.1103/physrevlett.86.4656] [Citation(s) in RCA: 162] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2001] [Indexed: 05/23/2023]
Abstract
Boron in MgB2 forms stacks of honeycomb layers with magnesium as a space filler. Band structure calculations indicate that Mg is substantially ionized, and the bands at the Fermi level derive mainly from B orbitals. Strong bonding with an ionic component and considerable metallic density of states yield a sizable electron-phonon coupling. Together with high phonon frequencies, which we estimate via zone-center frozen phonon calculations to be between 300 and 700 cm(-1), this produces a high critical temperature, consistent with recent experiments. Thus MgB2 can be viewed as an analog of the long sought, but still hypothetical, superconducting metallic hydrogen.
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Affiliation(s)
- J Kortus
- Georgetown University, Washington, D.C. 20057 and Center for Computational Materials Science, Code 6390, Naval Research Laboratory, Washington, D.C. 20375
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Mazin II, Savitskii EM, Uspenskii YA. Electron-phonon effects in 4d metals: calculation of coupling constant and resistivity. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0305-4608/14/1/017] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Abstract
Magnetic collapse in transition metal ions is predicted from first-principles computations at pressures reached in the Earth's lower mantle and core. Magnetic collapse would lead to marked changes in geophysically important properties, such as elasticity and conductivity, and also to different geochemical behavior, such as element partitioning, than estimated by extrapolating low-pressure data, and thus change the understanding of Earth's structure and evolution. Magnetic collapse results from band widening rather than from changes in crystal field splitting under pressure. Seismic anomalies in the outer core and the lowermost mantle may be due to magnetic collapse of ferrous iron, dissolved in iron liquid in the outer core, and in solution in magnesiowustite in the lowermost mantle.
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Affiliation(s)
- RE Cohen
- R. E. Cohen and I. I. Mazin, Geophysical Laboratory and Center for High-Pressure Research, Carnegie Institution of Washington, 5251 Broad Branch Road, NW, Washington, DC 20015, USA. D. G. Isaak, Institute of Geophysics and Planetary Physics, University of California at Los Angeles, Los Angeles, CA 90095-1567, and Department of Mathematics and Physics, Azusa Pacific University, Azusa, CA 91702, USA
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Goncharov AF, Eggert JH, Mazin II, Hemley RJ, Mao H. Raman excitations and orientational ordering in deuterium at high pressure. Phys Rev B Condens Matter 1996; 54:R15590-R15593. [PMID: 9985709 DOI: 10.1103/physrevb.54.r15590] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Goncharov AF, Mazin II, Eggert JH, Hemley RJ, Mao H. Invariant points and phase transitions in deuterium at megabar pressures. Phys Rev Lett 1995; 75:2514-2517. [PMID: 10059331 DOI: 10.1103/physrevlett.75.2514] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Mazin II, Cohen RE. Insulator-metal transition in solid hydrogen: Implication of electronic-structure calculations for recent experiments. Phys Rev B Condens Matter 1995; 52:R8597-R8600. [PMID: 9979903 DOI: 10.1103/physrevb.52.r8597] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Liechtenstein AI, Mazin II, Andersen OK. s-wave superconductivity from an antiferromagnetic spin-fluctuation model for bilayer materials. Phys Rev Lett 1995; 74:2303-2306. [PMID: 10057894 DOI: 10.1103/physrevlett.74.2303] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Krantz MC, Mazin II, Leach DH, Lee WY, Cardona M. Normal-state electronic Raman-scattering efficiencies of YBa2Cu3O7- delta, Bi2Sr2CaCu2O8, and Tl2Ba2Ca2Cu3O10: Effects of local-density-approximation Fermi-surface mass fluctuations. Phys Rev B Condens Matter 1995; 51:5949-5954. [PMID: 9979509 DOI: 10.1103/physrevb.51.5949] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Liechtenstein AI, Mazin II. Quantitative model for the superconductivity suppression in R1-xPrxBa2Cu3O7 with different rare earths. Phys Rev Lett 1995; 74:1000-1003. [PMID: 10058902 DOI: 10.1103/physrevlett.74.1000] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Jepsen O, Mazin II, Liechtenstein AI, Andersen OK, Rodriguez CO. Momentum dependence of the linewidth of Raman-active phonons in the normal state of YBa2Cu3O7. Phys Rev B Condens Matter 1995; 51:3961-3964. [PMID: 9979226 DOI: 10.1103/physrevb.51.3961] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Mazin II, Liechtenstein AI, Jepsen O, Andersen OK, Rodriguez CO. Displacive excitation of coherent phonons in YBa2Cu3O7. Phys Rev B Condens Matter 1994; 49:9210-9213. [PMID: 10009709 DOI: 10.1103/physrevb.49.9210] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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