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Suzuki H, Wang L, Bertinshaw J, Strand HUR, Käser S, Krautloher M, Yang Z, Wentzell N, Parcollet O, Jerzembeck F, Kikugawa N, Mackenzie AP, Georges A, Hansmann P, Gretarsson H, Keimer B. Distinct spin and orbital dynamics in Sr 2RuO 4. Nat Commun 2023; 14:7042. [PMID: 37923750 PMCID: PMC10624926 DOI: 10.1038/s41467-023-42804-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2023] [Accepted: 10/20/2023] [Indexed: 11/06/2023] Open
Abstract
The unconventional superconductor Sr2RuO4 has long served as a benchmark for theories of correlated-electron materials. The determination of the superconducting pairing mechanism requires detailed experimental information on collective bosonic excitations as potential mediators of Cooper pairing. We have used Ru L3-edge resonant inelastic x-ray scattering to obtain comprehensive maps of the electronic excitations of Sr2RuO4 over the entire Brillouin zone. We observe multiple branches of dispersive spin and orbital excitations associated with distinctly different energy scales. The spin and orbital dynamical response functions calculated within the dynamical mean-field theory are in excellent agreement with the experimental data. Our results highlight the Hund metal nature of Sr2RuO4 and provide key information for the understanding of its unconventional superconductivity.
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Affiliation(s)
- H Suzuki
- Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, D-70569, Stuttgart, Germany.
- Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai, 980-8578, Japan.
- Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, Sendai, 980-8578, Japan.
| | - L Wang
- Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, D-70569, Stuttgart, Germany
| | - J Bertinshaw
- Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, D-70569, Stuttgart, Germany
| | - H U R Strand
- School of Science and Technology, Örebro University, Fakultetsgatan 1, SE-701 82, Örebro, Sweden
- Institute for Molecules and Materials, Radboud University, 6525 AJ, Nijmegen, the Netherlands
| | - S Käser
- Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, D-70569, Stuttgart, Germany
- Department of Physics, Friedrich-Alexander-University (FAU) of Erlangen-Nürnberg, 91058, Erlangen, Germany
| | - M Krautloher
- Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, D-70569, Stuttgart, Germany
| | - Z Yang
- Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, D-70569, Stuttgart, Germany
| | - N Wentzell
- Center for Computational Quantum Physics, Flatiron Institute, Simons Foundation, 162 5th Avenue, New York, 10010, USA
| | - O Parcollet
- Center for Computational Quantum Physics, Flatiron Institute, Simons Foundation, 162 5th Avenue, New York, 10010, USA
- Université Paris-Saclay, CNRS, CEA, Institut de physique théorique, 91191, Gif-sur-Yvette, France
| | - F Jerzembeck
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187, Dresden, Germany
| | - N Kikugawa
- National Institute for Materials Science, Tsukuba, Ibaraki, 305-0003, Japan
| | - A P Mackenzie
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187, Dresden, Germany
| | - A Georges
- Center for Computational Quantum Physics, Flatiron Institute, Simons Foundation, 162 5th Avenue, New York, 10010, USA
- Collége de France, 11 place Marcelin Berthelot, 75005, Paris, France
- Centre de Physique Théorique (CPHT), CNRS, Ecole Polytechnique, IP Paris, 91128, Palaiseau, France
- Department of Quantum Matter Physics, University of Geneva, 24 Quai Ernest-Ansermet, 1211, Geneva 4, Switzerland
| | - P Hansmann
- Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, D-70569, Stuttgart, Germany
- Department of Physics, Friedrich-Alexander-University (FAU) of Erlangen-Nürnberg, 91058, Erlangen, Germany
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187, Dresden, Germany
| | - H Gretarsson
- Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, D-70569, Stuttgart, Germany.
- Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, D-22607, Hamburg, Germany.
| | - B Keimer
- Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, D-70569, Stuttgart, Germany.
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Singh K, Sihi A, Pandey SK, Mukherjee K. Evidence of charge susceptibility and multiple f- chybridization configurations with the La doping in CeGe: a DFT + DMFT study. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2023; 35. [PMID: 37161911 DOI: 10.1088/1361-648x/acd09a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2023] [Accepted: 04/26/2023] [Indexed: 05/11/2023]
Abstract
Kondo coupling has been extensively investigated in several Ce-based systems. However, the search for materials showing the interplay between the Kondo effect, spin-orbit interaction, and crystal-field effect along with the presence of local charge susceptibility; remains a challenge for the condensed matter community. Actually, in Ce-based systems, the strong coupling of the conduction electrons to the local magnetic moments usually hides these properties. Here, we present a detailed investigation of Ce0.6La0.4Ge through a combined density functional theory and dynamic mean-field theory study. Our investigations give evidence of the significant charge susceptibility and the multiple differentf-chybridization configurations. The weakening of the magnetization owing to the dilution of the Ce-site is the main cause for the appearance of such properties, which is believed to occur due to the presence of the relevant local moment andf-chybridization over the competition with the on-site Coulomb interaction.
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Affiliation(s)
- Karan Singh
- School of Physical Sciences, Indian Institute of Technology Mandi, Mandi 175075, Himachal Pradesh, India
| | - Antik Sihi
- School of Physical Sciences, Indian Institute of Technology Mandi, Mandi 175075, Himachal Pradesh, India
| | - Sudhir K Pandey
- School of Mechanical and Materials Engineering, Indian Institute of Technology Mandi, Mandi 175075, Himachal Pradesh, India
| | - K Mukherjee
- School of Physical Sciences, Indian Institute of Technology Mandi, Mandi 175075, Himachal Pradesh, India
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3
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Ryee S, Wehling TO. Switching between Mott-Hubbard and Hund Physics in Moiré Quantum Simulators. NANO LETTERS 2023; 23:573-579. [PMID: 36622289 DOI: 10.1021/acs.nanolett.2c04169] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
Mott-Hubbard and Hund electron correlations have been realized thus far in separate classes of materials. Here, we show that a single moiré homobilayer encompasses both kinds of physics in a controllable manner. We develop a microscopic multiband model that we solve by dynamical mean-field theory to nonperturbatively address the local many-body correlations. We demonstrate how tuning with twist angle, dielectric screening, and hole density allows us to switch between Mott-Hubbard and Hund correlated states in a twisted WSe2 bilayer. The underlying mechanism is based on controlling Coulomb-interaction-driven orbital polarization and the energetics of concomitant local singlet and triplet spin configurations. From a comparison to recent experimental transport data, we find signatures of a filling-controlled transition from a triplet charge-transfer insulator to a Hund-Mott metal. Our finding establishes twisted transition-metal dichalcogenides as a tunable platform for exotic phases of quantum matter emerging from large local spin moments.
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Affiliation(s)
- Siheon Ryee
- I. Institute of Theoretical Physics, University of Hamburg, Notkestrasse 9, 22607Hamburg, Germany
| | - Tim O Wehling
- I. Institute of Theoretical Physics, University of Hamburg, Notkestrasse 9, 22607Hamburg, Germany
- The Hamburg Centre for Ultrafast Imaging, Luruper Chaussee 149, 22761Hamburg, Germany
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4
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Nomura Y, Sakai S, Arita R. Fermi Surface Expansion above Critical Temperature in a Hund Ferromagnet. PHYSICAL REVIEW LETTERS 2022; 128:206401. [PMID: 35657875 DOI: 10.1103/physrevlett.128.206401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2021] [Revised: 02/23/2022] [Accepted: 04/25/2022] [Indexed: 06/15/2023]
Abstract
Using a cluster extension of the dynamical mean-field theory, we show that strongly correlated metals subject to Hund's physics exhibit significant electronic structure modulations above magnetic transition temperatures. In particular, in a ferromagnet having a large local moment due to Hund's coupling (Hund's ferromagnet), the Fermi surface expands even above the Curie temperature (T_{C}) as if a spin polarization occurred. Behind this phenomenon, effective "Hund's physics" works in momentum space, originating from ferromagnetic fluctuations in the strong-coupling regime. The resulting significantly momentum-dependent (spatially nonlocal) electron correlations induce an electronic structure reconstruction involving a Fermi surface volume change and a redistribution of the momentum-space occupation. Our finding will give a deeper insight into the physics of Hund's ferromagnets above T_{C}.
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Affiliation(s)
- Yusuke Nomura
- RIKEN Center for Emergent Matter Science, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Shiro Sakai
- RIKEN Center for Emergent Matter Science, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Ryotaro Arita
- RIKEN Center for Emergent Matter Science, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
- Department of Applied Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
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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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Maurya AK, Sarder MTH, Medhi A. Ground state of a three-band Hubbard model with Hund's coupling: Janus-faced behavior in presence of magnetic order. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:425603. [PMID: 34298529 DOI: 10.1088/1361-648x/ac1766] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2021] [Accepted: 07/23/2021] [Indexed: 06/13/2023]
Abstract
We study the ground state of the three-band degenerate Hubbard model on a square lattice at integer fillings using the variational slave-spin mean field method. At half-filling, the method reproduces the well known result that the ground state is antiferromagnetic (AF) insulating at smaller values of Hubbard onsite repulsionU, while it becomes Mott insulating with Néel AF order at higherU. Away from half-filling, for two particles per site, we show that the model supports a ferromagnetic (FM) metallic state with fully polarized spins at sufficiently largeU. The FM state occurs irrespective of the value of Hund's couplingJ. The ferromagnetism atJ= 0 can be explained by the Stoner mechanism while that forJ> 0 is shown to arise from the superexchange process. At this band filling, the Hund's couplingJis known to have the Janus-faced effect on electronic correlations where it enhances correlations at smallerUwhile reducing it at higherU. We show that these two effects are separated by the paramagnetic (PM) to FM transition point. The former effect is obtained at the PM state while the latter occurs in the FM state. The FM phase also occurs for one particle per site but here Hund's couplingJreduces the effect of electronic correlations at allU.
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Affiliation(s)
- Arun Kumar Maurya
- Indian Institute of Science Education and Research Thiruvananthapuram, Kerala 695551, India
| | | | - Amal Medhi
- Indian Institute of Science Education and Research Thiruvananthapuram, Kerala 695551, India
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7
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Ryee S, Han MJ, Choi S. Hund Physics Landscape of Two-Orbital Systems. PHYSICAL REVIEW LETTERS 2021; 126:206401. [PMID: 34110184 DOI: 10.1103/physrevlett.126.206401] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2020] [Revised: 02/10/2021] [Accepted: 03/29/2021] [Indexed: 06/12/2023]
Abstract
Motivated by the recent discovery of superconductivity in infinite-layer nickelates RE_{1-δ}Sr_{δ}NiO_{2} (RE=Nd, Pr), we study the role of Hund coupling J in a quarter-filled two-orbital Hubbard model, which has been on the periphery of the attention. A region of negative effective Coulomb interaction of this model is revealed to be differentiated from three- and five-orbital models in their typical Hund metal active fillings. We identify distinctive regimes including four different correlated metals, one of which stems from the proximity to a Mott insulator, while the other three, which we call "intermediate" metal, weak Hund metal, and valence-skipping metal, from the effect of J being away from Mottness. Defining criteria characterizing these metals is suggested, establishing the existence of Hund metallicity in two-orbital systems.
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Affiliation(s)
- Siheon Ryee
- Department of Physics, KAIST, Daejeon 34141, Republic of Korea
| | - Myung Joon Han
- Department of Physics, KAIST, Daejeon 34141, Republic of Korea
| | - Sangkook Choi
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
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8
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Direct observation of kink evolution due to Hund's coupling on approach to metal-insulator transition in NiS 2-xSe x. Nat Commun 2021; 12:1208. [PMID: 33623023 PMCID: PMC7902648 DOI: 10.1038/s41467-021-21460-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2020] [Accepted: 01/15/2021] [Indexed: 11/24/2022] Open
Abstract
Understanding characteristic energy scales is a fundamentally important issue in the study of strongly correlated systems. In multiband systems, an energy scale is affected not only by the effective Coulomb interaction but also by the Hund’s coupling. Direct observation of such energy scale has been elusive so far in spite of extensive studies. Here, we report the observation of a kink structure in the low energy dispersion of NiS2−xSex and its characteristic evolution with x, by using angle resolved photoemission spectroscopy. Dynamical mean field theory calculation combined with density functional theory confirms that this kink originates from Hund’s coupling. We find that the abrupt deviation from the Fermi liquid behavior in the electron self-energy results in the kink feature at low energy scale and that the kink is directly related to the coherence-incoherence crossover temperature scale. Our results mark the direct observation of the evolution of the characteristic temperature scale via kink features in the spectral function, which is the hallmark of Hund’s physics in the multiorbital system. A decisive spectroscopic evidence of the Hund’s coupling energy scale in multi-orbital correlated systems has been lacking. Here, the authors identify a kink feature due to Hund´s coupling in the spectral function of NiS2xSex as they track its evolution across the Mott-insulator transition.
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9
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Karp J, Bramberger M, Grundner M, Schollwöck U, Millis AJ, Zingl M. Sr_{2}MoO_{4} and Sr_{2}RuO_{4}: Disentangling the Roles of Hund's and van Hove Physics. PHYSICAL REVIEW LETTERS 2020; 125:166401. [PMID: 33124840 DOI: 10.1103/physrevlett.125.166401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2020] [Accepted: 09/22/2020] [Indexed: 06/11/2023]
Abstract
Sr_{2}MoO_{4} is isostructural to the unconventional superconductor Sr_{2}RuO_{4} but with two electrons instead of two holes in the Mo/Ru-t_{2g} orbitals. Both materials are Hund's metals, but while Sr_{2}RuO_{4} has a van Hove singularity in close proximity to the Fermi surface, the van Hove singularity of Sr_{2}MoO_{4} is far from the Fermi surface. By using density functional plus dynamical mean-field theory, we determine the relative influence of van Hove and Hund's metal physics on the correlation properties. We show that theoretically predicted signatures of Hund's metal physics occur on the occupied side of the electronic spectrum of Sr_{2}MoO_{4}, identifying Sr_{2}MoO_{4} as an ideal candidate system for a direct experimental confirmation of the theoretical concept of Hund's metals via photoemission spectroscopy.
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Affiliation(s)
- Jonathan Karp
- Department of Applied Physics and Applied Math, Columbia University, New York, New York 10027, USA
| | - Max Bramberger
- Arnold Sommerfeld Center of Theoretical Physics, Department of Physics, University of Munich, Theresienstrasse 37, 80333 Munich, Germany
- Munich Center for Quantum Science and Technology (MCQST), Schellingstrasse 4, 80799 Munich, Germany
| | - Martin Grundner
- Arnold Sommerfeld Center of Theoretical Physics, Department of Physics, University of Munich, Theresienstrasse 37, 80333 Munich, Germany
- Munich Center for Quantum Science and Technology (MCQST), Schellingstrasse 4, 80799 Munich, Germany
| | - Ulrich Schollwöck
- Arnold Sommerfeld Center of Theoretical Physics, Department of Physics, University of Munich, Theresienstrasse 37, 80333 Munich, Germany
- Munich Center for Quantum Science and Technology (MCQST), Schellingstrasse 4, 80799 Munich, Germany
| | - Andrew J Millis
- Department of Physics, Columbia University, New York, New York 10027, USA
- Center for Computational Quantum Physics, Flatiron Institute, 162 5th Avenue, New York, New York 10010, USA
| | - Manuel Zingl
- Center for Computational Quantum Physics, Flatiron Institute, 162 5th Avenue, New York, New York 10010, USA
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10
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van Loon EGCP, Krien F, Katanin AA. Bethe-Salpeter Equation at the Critical End Point of the Mott Transition. PHYSICAL REVIEW LETTERS 2020; 125:136402. [PMID: 33034474 DOI: 10.1103/physrevlett.125.136402] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/2020] [Revised: 08/17/2020] [Accepted: 08/21/2020] [Indexed: 06/11/2023]
Abstract
Strong repulsive interactions between electrons can lead to a Mott metal-insulator transition. The dynamical mean-field theory (DMFT) explains the critical end point and the hysteresis region usually in terms of single-particle concepts, such as the spectral function and the quasiparticle weight. In this Letter, we reconsider the critical end point of the metal-insulator transition on the DMFT's two-particle level. We show that the relevant eigenvalue and eigenvector of the nonlocal Bethe-Salpeter kernel in the charge channel provide a unified picture of the hysteresis region and of the critical end point of the Mott transition. In particular, they simultaneously explain the thermodynamics of the hysteresis region and the iterative stability of the DMFT equations. This analysis paves the way for a deeper understanding of phase transitions in correlated materials.
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Affiliation(s)
- Erik G C P van Loon
- Institut für Theoretische Physik, Universität Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany
- Bremen Center for Computational Materials Science, Universität Bremen, Am Fallturm 1a, 28359 Bremen, Germany
| | - Friedrich Krien
- Jožef Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia
| | - Andrey A Katanin
- Moscow Institute of Physics and Technology, 141701 Dolgoprudny, Russia
- M. N. Mikheev Institute of Metal Physics, Russian Academy of Sciences, 620108 Yekaterinburg, Russia
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11
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Wang Y, Walter E, Lee SSB, Stadler KM, von Delft J, Weichselbaum A, Kotliar G. Global Phase Diagram of a Spin-Orbital Kondo Impurity Model and the Suppression of Fermi-Liquid Scale. PHYSICAL REVIEW LETTERS 2020; 124:136406. [PMID: 32302177 DOI: 10.1103/physrevlett.124.136406] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/04/2019] [Accepted: 02/28/2020] [Indexed: 06/11/2023]
Abstract
Many correlated metallic materials are described by Landau Fermi-liquid theory at low energies, but for Hund metals the Fermi-liquid coherence scale T_{FL} is found to be surprisingly small. In this Letter, we study the simplest impurity model relevant for Hund metals, the three-channel spin-orbital Kondo model, using the numerical renormalization group (NRG) method and compute its global phase diagram. In this framework, T_{FL} becomes arbitrarily small close to two new quantum critical points that we identify by tuning the spin or spin-orbital Kondo couplings into the ferromagnetic regimes. We find quantum phase transitions to a singular Fermi-liquid or a novel non-Fermi-liquid phase. The new non-Fermi-liquid phase shows frustrated behavior involving alternating overscreenings in spin and orbital sectors, with universal power laws in the spin (ω^{-1/5}), orbital (ω^{1/5}) and spin-orbital (ω^{1}) dynamical susceptibilities. These power laws, and the NRG eigenlevel spectra, can be fully understood using conformal field theory arguments, which also clarify the nature of the non-Fermi-liquid phase.
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Affiliation(s)
- Y Wang
- Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - E Walter
- Arnold Sommerfeld Center for Theoretical Physics, Center for NanoScience, and Munich Center for Quantum Science and Technology, Ludwig-Maximilians-Universität München, 80333 Munich, Germany
| | - S-S B Lee
- Arnold Sommerfeld Center for Theoretical Physics, Center for NanoScience, and Munich Center for Quantum Science and Technology, Ludwig-Maximilians-Universität München, 80333 Munich, Germany
| | - K M Stadler
- Arnold Sommerfeld Center for Theoretical Physics, Center for NanoScience, and Munich Center for Quantum Science and Technology, Ludwig-Maximilians-Universität München, 80333 Munich, Germany
| | - J von Delft
- Arnold Sommerfeld Center for Theoretical Physics, Center for NanoScience, and Munich Center for Quantum Science and Technology, Ludwig-Maximilians-Universität München, 80333 Munich, Germany
| | - A Weichselbaum
- Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, New York 11973, USA
- Arnold Sommerfeld Center for Theoretical Physics, Center for NanoScience, and Munich Center for Quantum Science and Technology, Ludwig-Maximilians-Universität München, 80333 Munich, Germany
| | - G Kotliar
- Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, New York 11973, USA
- Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08856, USA
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12
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Kugler FB, Zingl M, Strand HUR, Lee SSB, von Delft J, Georges A. Strongly Correlated Materials from a Numerical Renormalization Group Perspective: How the Fermi-Liquid State of Sr_{2}RuO_{4} Emerges. PHYSICAL REVIEW LETTERS 2020; 124:016401. [PMID: 31976705 DOI: 10.1103/physrevlett.124.016401] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2019] [Indexed: 06/10/2023]
Abstract
The crossover from fluctuating atomic constituents to a collective state as one lowers temperature or energy is at the heart of the dynamical mean-field theory description of the solid state. We demonstrate that the numerical renormalization group is a viable tool to monitor this crossover in a real-materials setting. The renormalization group flow from high to arbitrarily small energy scales clearly reveals the emergence of the Fermi-liquid state of Sr_{2}RuO_{4}. We find a two-stage screening process, where orbital fluctuations are screened at much higher energies than spin fluctuations, and Fermi-liquid behavior, concomitant with spin coherence, below a temperature of 25 K. By computing real-frequency correlation functions, we directly observe this spin-orbital scale separation and show that the van Hove singularity drives strong orbital differentiation. We extract quasiparticle interaction parameters from the low-energy spectrum and find an effective attraction in the spin-triplet sector.
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Affiliation(s)
- Fabian B Kugler
- Arnold Sommerfeld Center for Theoretical Physics, Center for NanoScience, and Munich Center for Quantum Science and Technology, Ludwig-Maximilians-Universität München, 80333 Munich, Germany
| | - Manuel Zingl
- Center for Computational Quantum Physics, Flatiron Institute, 162 5th Avenue, New York, New York 10010, USA
| | - Hugo U R Strand
- Center for Computational Quantum Physics, Flatiron Institute, 162 5th Avenue, New York, New York 10010, USA
| | - Seung-Sup B Lee
- Arnold Sommerfeld Center for Theoretical Physics, Center for NanoScience, and Munich Center for Quantum Science and Technology, Ludwig-Maximilians-Universität München, 80333 Munich, Germany
| | - Jan von Delft
- Arnold Sommerfeld Center for Theoretical Physics, Center for NanoScience, and Munich Center for Quantum Science and Technology, Ludwig-Maximilians-Universität München, 80333 Munich, Germany
| | - Antoine Georges
- Center for Computational Quantum Physics, Flatiron Institute, 162 5th Avenue, New York, New York 10010, USA
- Collège de France, 11 place Marcelin Berthelot, 75005 Paris, France
- Centre de Physique Théorique, CNRS, Ecole Polytechnique, IP Paris, 91128 Palaiseau, France
- Department of Quantum Matter Physics, University of Geneva, 1211 Geneva 4, Switzerland
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13
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Signatures of Mottness and Hundness in archetypal correlated metals. Nat Commun 2019; 10:2721. [PMID: 31221960 PMCID: PMC6586627 DOI: 10.1038/s41467-019-10257-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2017] [Accepted: 04/26/2019] [Indexed: 02/06/2023] Open
Abstract
Physical properties of multi-orbital materials depend not only on the strength of the effective interactions among the valence electrons but also on their type. Strong correlations are caused by either Mott physics that captures the Coulomb repulsion among charges, or Hund physics that aligns the spins in different orbitals. We identify four energy scales marking the onset and the completion of screening in orbital and spin channels. The differences in these scales, which are manifest in the temperature dependence of the local spectrum and of the charge, spin and orbital susceptibilities, provide clear signatures distinguishing Mott and Hund physics. We illustrate these concepts with realistic studies of two archetypal strongly correlated materials, and corroborate the generality of our conclusions with a model Hamiltonian study.
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14
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Isidori A, Berović M, Fanfarillo L, De' Medici L, Fabrizio M, Capone M. Charge Disproportionation, Mixed Valence, and Janus Effect in Multiorbital Systems: A Tale of Two Insulators. PHYSICAL REVIEW LETTERS 2019; 122:186401. [PMID: 31144864 DOI: 10.1103/physrevlett.122.186401] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2018] [Revised: 04/12/2019] [Indexed: 06/09/2023]
Abstract
Multiorbital Hubbard models host strongly correlated "Hund's metals" even for interactions much stronger than the bandwidth. We characterize this interaction-resilient metal as a mixed-valence state. In particular, it can be pictured as a bridge between two strongly correlated insulators: a high-spin Mott insulator and a charge-disproportionated insulator which is stabilized by a very large Hund's coupling. This picture is confirmed comparing models with negative and positive Hund's coupling for different fillings. Our results provide a characterization of the Hund's metal state and connect its presence with charge disproportionation, which has indeed been observed in chromates and proposed to play a role in iron-based superconductors.
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Affiliation(s)
- Aldo Isidori
- International School for Advanced Studies (SISSA), Via Bonomea 265, I-34136 Trieste, Italy
| | - Maja Berović
- International School for Advanced Studies (SISSA), Via Bonomea 265, I-34136 Trieste, Italy
| | - Laura Fanfarillo
- International School for Advanced Studies (SISSA), Via Bonomea 265, I-34136 Trieste, Italy
- CNR-IOM Democritos, Via Bonomea 265, I-34136 Trieste, Italy
| | - Luca De' Medici
- Laboratoire de Physique et d'Étude des Matériaux, UMR8213 CNRS/ESPCI/UPMC, Paris, France
| | - Michele Fabrizio
- International School for Advanced Studies (SISSA), Via Bonomea 265, I-34136 Trieste, Italy
| | - Massimo Capone
- International School for Advanced Studies (SISSA), Via Bonomea 265, I-34136 Trieste, Italy
- CNR-IOM Democritos, Via Bonomea 265, I-34136 Trieste, Italy
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15
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Avella A, Oleś AM, Horsch P. Defect-Induced Orbital Polarization and Collapse of Orbital Order in Doped Vanadium Perovskites. PHYSICAL REVIEW LETTERS 2019; 122:127206. [PMID: 30978090 DOI: 10.1103/physrevlett.122.127206] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2018] [Indexed: 06/09/2023]
Abstract
We explore mechanisms of orbital-order decay in the doped Mott insulators R_{1-x}(Sr,Ca)_{x}VO_{3} (R=Pr,Y,La) caused by charged (Sr,Ca) defects. Our unrestricted Hartree-Fock analysis focuses on the combined effect of random charged impurities and associated doped holes up to x=0.5. The study is based on a generalized multiband Hubbard model for the relevant vanadium t_{2g} electrons and includes the long-range (i) Coulomb potentials of defects and (ii) electron-electron interactions. We show that the rotation of t_{2g} orbitals, induced by the electric field of defects, is a very efficient perturbation that largely controls the suppression of orbital order in these compounds. We investigate the inverse participation number spectra and find that electron states remain localized on few sites even in the regime where orbital order is collapsed. From the change of kinetic and superexchange energy, we can conclude that the motion of doped holes, which is the dominant effect for the reduction of magnetic order in high-T_{c} compounds, is of secondary importance here.
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Affiliation(s)
- Adolfo Avella
- Dipartimento di Fisica "E.R. Caianiello," Università degli Studi di Salerno, I-84084 Fisciano (SA), Italy
- CNR-SPIN, UOS di Salerno, I-84084 Fisciano (SA), Italy
- Unità CNISM di Salerno, Università degli Studi di Salerno, I-84084 Fisciano (SA), Italy
| | - Andrzej M Oleś
- Marian Smoluchowski Institute of Physics, Jagiellonian University, Prof. S. Łojasiewicza 11, PL-30348 Kraków, Poland
- Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
| | - Peter Horsch
- Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
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16
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17
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Lee TH, Chubukov A, Miao H, Kotliar G. Pairing Mechanism in Hund's Metal Superconductors and the Universality of the Superconducting Gap to Critical Temperature Ratio. PHYSICAL REVIEW LETTERS 2018; 121:187003. [PMID: 30444397 DOI: 10.1103/physrevlett.121.187003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2018] [Revised: 08/20/2018] [Indexed: 06/09/2023]
Abstract
We analyze a simple model containing the physical ingredients of a Hund's metal, the local spin fluctuations with power-law correlators, (Ω_{0}/|Ω|)^{γ}, with γ greater than one, interacting with electronic quasiparticles. While the critical temperature and the gap change significantly with varying parameters, the 2Δ_{max}/k_{B}T_{c} remains close to twice the BCS value in agreement with experimental observations in the iron-based superconductors (FeSC).
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Affiliation(s)
- Tsung-Han Lee
- Physics and Astronomy Department, Rutgers University, Piscataway, New Jersey 08854, USA
| | - Andrey Chubukov
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - Hu Miao
- Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Gabriel Kotliar
- Physics and Astronomy Department, Rutgers University, Piscataway, New Jersey 08854, USA
- Brookhaven National Laboratory, Upton, New York 11973, USA
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18
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Fernández J, Roura-Bas P, Camjayi A, Aligia AA. Two-stage three-channel Kondo physics for an FePc molecule on the Au(1 1 1) surface. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:374003. [PMID: 30095081 DOI: 10.1088/1361-648x/aad973] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We study an impurity Anderson model to describe an iron phthalocyanine (FePc) molecule on Au(1 1 1), motivated by previous results of scanning tunneling spectroscopy (STS) and theoretical studies. The model hybridizes a spin doublet consisting in one hole at the [Formula: see text] orbital of iron and two degenerate doublets corresponding to one hole either in the 3d xz or in the 3d yz orbital (called π orbitals) with two degenerate Hund-rule triplets with one hole in the 3d z orbital and another one in a π orbital. We solve the model using a slave-boson mean-field approximation (SBMFA). For reasonable parameters we can describe very well the observed STS spectrum between sample bias -60 mV to 20 mV. For these parameters the Kondo effect takes place in two stages, with different energy scales [Formula: see text] corresponding to the Kondo temperatures related with the hopping of the z 2 and π orbitals respectively. There is a strong interference between the different channels and the Kondo temperatures, particularly the lowest one is strongly reduced compared with the value in the absence of the competing channel.
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Affiliation(s)
- J Fernández
- Centro Atómico Bariloche and Instituto Balseiro, Comisión Nacional de Energía Atómica, CONICET 8400 Bariloche, Argentina
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Abstract
Correlated electron materials display a rich variety of notable properties ranging from unconventional superconductivity to metal-insulator transitions. These properties are of interest from the point of view of applications but are hard to treat theoretically, as they result from multiple competing energy scales. Although possible in more weakly correlated materials, theoretical design and spectroscopy of strongly correlated electron materials have been a difficult challenge for many years. By treating all the relevant energy scales with sufficient accuracy, complementary advances in Green's functions and quantum Monte Carlo methods open a path to first-principles computational property predictions in this class of materials.
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Affiliation(s)
- Paul R C Kent
- Computational Sciences and Engineering Division and Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
| | - Gabriel Kotliar
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA. .,Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA
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20
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Kim M, Mravlje J, Ferrero M, Parcollet O, Georges A. Spin-Orbit Coupling and Electronic Correlations in Sr_{2}RuO_{4}. PHYSICAL REVIEW LETTERS 2018; 120:126401. [PMID: 29694056 DOI: 10.1103/physrevlett.120.126401] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2017] [Revised: 02/20/2018] [Indexed: 06/08/2023]
Abstract
We investigate the interplay of spin-orbit coupling (SOC) and electronic correlations in Sr_{2}RuO_{4} using dynamical mean-field theory. We find that SOC does not affect the correlation-induced renormalizations, which validates Hund's metal picture of ruthenates even in the presence of the sizable SOC relevant to these materials. Nonetheless, SOC is found to change significantly the electronic structure at k points where a degeneracy applies in its absence. We explain why these two observations are consistent with one another and calculate the effects of SOC on the correlated electronic structure. The magnitude of these effects is found to depend on the energy of the quasiparticle state under consideration, leading us to introduce the notion of an energy-dependent quasiparticle spin-orbit coupling λ^{*}(ω). This notion is generally applicable to all materials in which both the spin-orbit coupling and electronic correlations are sizable.
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Affiliation(s)
- Minjae Kim
- Centre de Physique Théorique, École Polytechnique, CNRS, Université Paris-Saclay, 91128 Palaiseau, France
- Collège de France, 11 place Marcelin Berthelot, 75005 Paris, France
| | - Jernej Mravlje
- Jožef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia
| | - Michel Ferrero
- Centre de Physique Théorique, École Polytechnique, CNRS, Université Paris-Saclay, 91128 Palaiseau, France
- Collège de France, 11 place Marcelin Berthelot, 75005 Paris, France
| | - Olivier Parcollet
- Collège de France, 11 place Marcelin Berthelot, 75005 Paris, France
- Institut de Physique Théorique (IPhT), CEA, CNRS, 91191 Gif-sur-Yvette, France
| | - Antoine Georges
- Centre de Physique Théorique, École Polytechnique, CNRS, Université Paris-Saclay, 91128 Palaiseau, France
- Collège de France, 11 place Marcelin Berthelot, 75005 Paris, France
- Center for Computational Quantum Physics, Flatiron Institute, 162 Fifth avenue, New York, New York 10010, USA
- Department of Quantum Matter Physics, University of Geneva, 24 Quai Ernest-Ansermet, 1211 Geneva 4, Switzerland
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James AJA, Konik RM, Lecheminant P, Robinson NJ, Tsvelik AM. Non-perturbative methodologies for low-dimensional strongly-correlated systems: From non-Abelian bosonization to truncated spectrum methods. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2018; 81:046002. [PMID: 29480168 DOI: 10.1088/1361-6633/aa91ea] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We review two important non-perturbative approaches for extracting the physics of low-dimensional strongly correlated quantum systems. Firstly, we start by providing a comprehensive review of non-Abelian bosonization. This includes an introduction to the basic elements of conformal field theory as applied to systems with a current algebra, and we orient the reader by presenting a number of applications of non-Abelian bosonization to models with large symmetries. We then tie this technique into recent advances in the ability of cold atomic systems to realize complex symmetries. Secondly, we discuss truncated spectrum methods for the numerical study of systems in one and two dimensions. For one-dimensional systems we provide the reader with considerable insight into the methodology by reviewing canonical applications of the technique to the Ising model (and its variants) and the sine-Gordon model. Following this we review recent work on the development of renormalization groups, both numerical and analytical, that alleviate the effects of truncating the spectrum. Using these technologies, we consider a number of applications to one-dimensional systems: properties of carbon nanotubes, quenches in the Lieb-Liniger model, 1 + 1D quantum chromodynamics, as well as Landau-Ginzburg theories. In the final part we move our attention to consider truncated spectrum methods applied to two-dimensional systems. This involves combining truncated spectrum methods with matrix product state algorithms. We describe applications of this method to two-dimensional systems of free fermions and the quantum Ising model, including their non-equilibrium dynamics.
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Affiliation(s)
- Andrew J A James
- London Centre for Nanotechnology, University College London, Gordon Street, London WC1H 0AH, United Kingdom
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22
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De' Medici L. Hund's Induced Fermi-Liquid Instabilities and Enhanced Quasiparticle Interactions. PHYSICAL REVIEW LETTERS 2017; 118:167003. [PMID: 28474949 DOI: 10.1103/physrevlett.118.167003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2016] [Indexed: 06/07/2023]
Abstract
Hund's coupling is shown to generally favor, in a doped half-filled Mott insulator, an increase in the compressibility culminating in a Fermi-liquid instability towards phase separation. The largest effect is found near the frontier between an ordinary and an orbitally decoupled ("Hund's") metal. The increased compressibility implies an enhancement of quasiparticle scattering, thus favoring other possible symmetry breakings. This physics is shown to happen in simulations of the 122 Fe-based superconductors, possibly implying the relevance of this mechanism in the enhancement of the critical temperature for superconductivity.
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Affiliation(s)
- Luca De' Medici
- European Synchrotron Radiation Facility, 71 Avenue des Martyrs, Grenoble, France
- Laboratoire de Physique et Etude des Matériaux, UMR8213 CNRS/ESPCI/UPMC, Paris, France
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Kondo T, Ochi M, Nakayama M, Taniguchi H, Akebi S, Kuroda K, Arita M, Sakai S, Namatame H, Taniguchi M, Maeno Y, Arita R, Shin S. Orbital-Dependent Band Narrowing Revealed in an Extremely Correlated Hund's Metal Emerging on the Topmost Layer of Sr_{2}RuO_{4}. PHYSICAL REVIEW LETTERS 2016; 117:247001. [PMID: 28009182 DOI: 10.1103/physrevlett.117.247001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2016] [Indexed: 06/06/2023]
Abstract
We use a surface-selective angle-resolved photoemission spectroscopy and unveil the electronic nature on the topmost layer of Sr_{2}RuO_{4} crystal, consisting of slightly rotated RuO_{6} octahedrons. The γ band derived from the 4d_{xy} orbital is found to be about three times narrower than that for the bulk. This strongly contrasts with a subtle variation seen in the α and β bands derived from the one-dimensional 4d_{xz/yz}. This anomaly is reproduced by the dynamical mean-field theory calculations, introducing not only the on-site Hubbard interaction but also the significant Hund's coupling. We detect a coherence-to-incoherence crossover theoretically predicted for Hund's metals, which has been recognized only recently. The crossover temperature in the surface is about half that of the bulk, indicating that the naturally generated monolayer of reconstructed Sr_{2}RuO_{4} is extremely correlated and well isolated from the underlying crystal.
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Affiliation(s)
- Takeshi Kondo
- ISSP, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
| | - M Ochi
- Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan
- RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan
| | - M Nakayama
- ISSP, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
| | - H Taniguchi
- Department of Materials Science and Engineering, Iwate University, Morioka 020-8551, Japan
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - S Akebi
- ISSP, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
| | - K Kuroda
- ISSP, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
| | - M Arita
- Hiroshima Synchrotron Center, Hiroshima University, Higashi-Hiroshima 739-0046, Japan
| | - S Sakai
- RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan
| | - H Namatame
- Hiroshima Synchrotron Center, Hiroshima University, Higashi-Hiroshima 739-0046, Japan
| | - M Taniguchi
- Hiroshima Synchrotron Center, Hiroshima University, Higashi-Hiroshima 739-0046, Japan
- Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
| | - Y Maeno
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - R Arita
- RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan
| | - S Shin
- ISSP, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
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24
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Mravlje J, Georges A. Thermopower and Entropy: Lessons from Sr_{2}RuO_{4}. PHYSICAL REVIEW LETTERS 2016; 117:036401. [PMID: 27472124 DOI: 10.1103/physrevlett.117.036401] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2015] [Indexed: 06/06/2023]
Abstract
We calculate the in-plane Seebeck coefficient of Sr_{2}RuO_{4} within a framework combining electronic structure and dynamical mean-field theory. We show that its temperature dependence can be interpreted using entropic considerations based on the Kelvin formula and that it provides a meaningful probe of the crossover out of the Fermi liquid regime into an incoherent metal. This crossover proceeds in two stages: The entropy of spin degrees of freedom is released around room temperature, while orbital degrees of freedom remain quenched up to much higher temperatures. This is confirmed by a direct calculation of the corresponding susceptibilities and is a hallmark of "Hund's metals." We also calculate the c-axis thermopower and predict that it exceeds substantially the in-plane one at high temperature, a peculiar behavior which originates from an interlayer "hole-filtering" mechanism.
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Affiliation(s)
| | - Antoine Georges
- Collège de France, 11 place Marcelin Berthelot, 75005 Paris, France
- Centre de Physique Théorique, École Polytechnique, CNRS, 91128 Palaiseau Cedex, France
- DQMP, Université de Genève, 24 quai Ernest Ansermet, CH-1211 Genève, Switzerland
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Vildosola V, Pourovskii LV, Manuel LO, Roura-Bas P. Reliability of the one-crossing approximation in describing the Mott transition. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:485602. [PMID: 26565588 DOI: 10.1088/0953-8984/27/48/485602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We assess the reliability of the one-crossing approximation (OCA) approach in a quantitative description of the Mott transition in the framework of the dynamical mean field theory (DMFT). The OCA approach has been applied in conjunction with DMFT to a number of heavy-fermion, actinide, transition metal compounds and nanoscale systems. However, several recent studies in the framework of impurity models pointed out serious deficiencies of OCA and raised questions regarding its reliability. Here we consider a single band Hubbard model on the Bethe lattice at finite temperatures and compare the results of OCA to those of a numerically exact quantum Monte Carlo (QMC) method. The temperature-local repulsion U phase diagram for the particle-hole symmetric case obtained by OCA is in good agreement with that of QMC, with the metal-insulator transition captured very well. We find, however, that the insulator to metal transition is shifted to higher values of U and, simultaneously, correlations in the metallic phase are significantly overestimated. This counter-intuitive behaviour is due to simultaneous underestimations of the Kondo scale in the metallic phase and the size of the insulating gap. We trace the underestimation of the insulating gap to that of the second moment of the high-frequency expansion of the impurity spectral density. Calculations of the system away from the particle-hole symmetric case are also presented and discussed.
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Affiliation(s)
- V Vildosola
- Departmento de Física de la Materia Condensada, GIyA, CNEA (1650) San Martín, Provincia de Buenos Aires and Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Ciudad Autónoma de Buenas Aires, Argentina
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