1
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Posey VA, Turkel S, Rezaee M, Devarakonda A, Kundu AK, Ong CS, Thinel M, Chica DG, Vitalone RA, Jing R, Xu S, Needell DR, Meirzadeh E, Feuer ML, Jindal A, Cui X, Valla T, Thunström P, Yilmaz T, Vescovo E, Graf D, Zhu X, Scheie A, May AF, Eriksson O, Basov DN, Dean CR, Rubio A, Kim P, Ziebel ME, Millis AJ, Pasupathy AN, Roy X. Two-dimensional heavy fermions in the van der Waals metal CeSiI. Nature 2024; 625:483-488. [PMID: 38233620 DOI: 10.1038/s41586-023-06868-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2023] [Accepted: 11/14/2023] [Indexed: 01/19/2024]
Abstract
Heavy-fermion metals are prototype systems for observing emergent quantum phases driven by electronic interactions1-6. A long-standing aspiration is the dimensional reduction of these materials to exert control over their quantum phases7-11, which remains a significant challenge because traditional intermetallic heavy-fermion compounds have three-dimensional atomic and electronic structures. Here we report comprehensive thermodynamic and spectroscopic evidence of an antiferromagnetically ordered heavy-fermion ground state in CeSiI, an intermetallic comprising two-dimensional (2D) metallic sheets held together by weak interlayer van der Waals (vdW) interactions. Owing to its vdW nature, CeSiI has a quasi-2D electronic structure, and we can control its physical dimension through exfoliation. The emergence of coherent hybridization of f and conduction electrons at low temperature is supported by the temperature evolution of angle-resolved photoemission and scanning tunnelling spectra near the Fermi level and by heat capacity measurements. Electrical transport measurements on few-layer flakes reveal heavy-fermion behaviour and magnetic order down to the ultra-thin regime. Our work establishes CeSiI and related materials as a unique platform for studying dimensionally confined heavy fermions in bulk crystals and employing 2D device fabrication techniques and vdW heterostructures12 to manipulate the interplay between Kondo screening, magnetic order and proximity effects.
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Affiliation(s)
| | - Simon Turkel
- Physics Department, Columbia University, New York, NY, USA
- Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, NY, USA
| | - Mehdi Rezaee
- Physics Department, Harvard University, Cambridge, MA, USA
| | | | - Asish K Kundu
- Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, NY, USA
| | - Chin Shen Ong
- Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden
| | - Morgan Thinel
- Chemistry Department, Columbia University, New York, NY, USA
- Physics Department, Columbia University, New York, NY, USA
| | - Daniel G Chica
- Chemistry Department, Columbia University, New York, NY, USA
| | | | - Ran Jing
- Physics Department, Columbia University, New York, NY, USA
| | - Suheng Xu
- Physics Department, Columbia University, New York, NY, USA
| | - David R Needell
- Chemistry Department, Columbia University, New York, NY, USA
| | - Elena Meirzadeh
- Chemistry Department, Columbia University, New York, NY, USA
| | | | - Apoorv Jindal
- Physics Department, Columbia University, New York, NY, USA
| | - Xiaomeng Cui
- Physics Department, Harvard University, Cambridge, MA, USA
| | - Tonica Valla
- Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, NY, USA
- Donostia International Physics Center (DIPC), Donostia-San Sebastián, Spain
| | - Patrik Thunström
- Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden
| | - Turgut Yilmaz
- National Synchrotron Light Source II, Brookhaven National Lab, Upton, NY, USA
| | - Elio Vescovo
- National Synchrotron Light Source II, Brookhaven National Lab, Upton, NY, USA
| | - David Graf
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, USA
| | - Xiaoyang Zhu
- Chemistry Department, Columbia University, New York, NY, USA
| | - Allen Scheie
- Neutron Scattering Division, Oak Ridge National Lab, Oak Ridge, TN, USA
- MPA-Q, Los Alamos National Lab, Los Alamos, NM, USA
| | - Andrew F May
- Materials Science and Technology Division, Oak Ridge National Lab, Oak Ridge, TN, USA
| | - Olle Eriksson
- Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden
- Wallenberg Initiative Materials Science for Sustainability, Uppsala University, Uppsala, Sweden
| | - D N Basov
- Physics Department, Columbia University, New York, NY, USA
| | - Cory R Dean
- Physics Department, Columbia University, New York, NY, USA
| | - Angel Rubio
- Max Planck Institute for the Structure and Dynamics of Matter, Center for Free-Electron Laser Science and Department of Physics, Hamburg, Germany.
- Nano-Bio Spectroscopy Group and European Theoretical Spectroscopy Facility (ETSF), Departmento de Polímeros y Materiales Avanzados: Física, Química y Tecnología, Universidad del País Vasco (UPV/EHU), San Sebastián, Spain.
- Center for Computational Quantum Physics, Flatiron Institute, New York, NY, USA.
| | - Philip Kim
- Physics Department, Harvard University, Cambridge, MA, USA
| | | | - Andrew J Millis
- Physics Department, Columbia University, New York, NY, USA.
- Center for Computational Quantum Physics, Flatiron Institute, New York, NY, USA.
| | - Abhay N Pasupathy
- Physics Department, Columbia University, New York, NY, USA.
- Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, NY, USA.
| | - Xavier Roy
- Chemistry Department, Columbia University, New York, NY, USA.
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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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Wu Z, Fang Y, Su H, Xie W, Li P, Wu Y, Huang Y, Shen D, Thiagarajan B, Adell J, Cao C, Yuan H, Steglich F, Liu Y. Revealing the Heavy Quasiparticles in the Heavy-Fermion Superconductor CeCu_{2}Si_{2}. PHYSICAL REVIEW LETTERS 2021; 127:067002. [PMID: 34420319 DOI: 10.1103/physrevlett.127.067002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2020] [Revised: 02/28/2021] [Accepted: 06/28/2021] [Indexed: 06/13/2023]
Abstract
The superconducting order parameter of the first heavy-fermion superconductor CeCu_{2}Si_{2} is currently under debate. A key ingredient to understand its superconductivity and physical properties is the quasiparticle dispersion and Fermi surface, which remains elusive experimentally. Here, we present measurements from angle-resolved photoemission spectroscopy. Our results emphasize the key role played by the Ce 4f electrons for the low-temperature Fermi surface, highlighting a band-dependent conduction-f electron hybridization. In particular, we find a very heavy quasi-two-dimensional electron band near the bulk X point and moderately heavy three-dimensional hole pockets near the Z point. Comparison with theoretical calculations reveals the strong local correlation in this compound, calling for further theoretical studies. Our results provide the electronic basis to understand the heavy-fermion behavior and superconductivity; implications for the enigmatic superconductivity of this compound are also discussed.
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Affiliation(s)
- Zhongzheng Wu
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
| | - Yuan Fang
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
| | - Hang Su
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
| | - Wu Xie
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
| | - Peng Li
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
| | - Yi Wu
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
| | - Yaobo Huang
- Shanghai Institute of Applied Physics, Chinese Academy of Science, Shanghai 210800, China
| | - Dawei Shen
- State Key Laboratory of Functional Materials for Informatics and Center for Excellence in Superconducting Electronics, SIMIT, Chinese Academy of Science, Shanghai 200050, China
| | | | - Johan Adell
- MAX IV Laboratory, Lund University, P.O. Box 118, 221 00 Lund, Sweden
| | - Chao Cao
- Department of Physics, Hangzhou Normal University, Hangzhou 311121, China
| | - Huiqiu Yuan
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
- Zhejiang Province Key Laboratory of Quantum Technology and Device, Zhejiang University, Hangzhou 310058, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Frank Steglich
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
| | - Yang Liu
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
- Zhejiang Province Key Laboratory of Quantum Technology and Device, Zhejiang University, Hangzhou 310058, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
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4
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Evolution of the Kondo lattice electronic structure above the transport coherence temperature. Proc Natl Acad Sci U S A 2020; 117:23467-23476. [PMID: 32887802 DOI: 10.1073/pnas.2001778117] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The temperature-dependent evolution of the Kondo lattice is a long-standing topic of theoretical and experimental investigation and yet it lacks a truly microscopic description of the relation of the basic f-c hybridization processes to the fundamental temperature scales of Kondo screening and Fermi-liquid lattice coherence. Here, the temperature dependence of f-c hybridized band dispersions and Fermi-energy f spectral weight in the Kondo lattice system CeCoIn5 is investigated using f-resonant angle-resolved photoemission spectroscopy (ARPES) with sufficient detail to allow direct comparison to first-principles dynamical mean-field theory (DMFT) calculations containing full realism of crystalline electric-field states. The ARPES results, for two orthogonal (001) and (100) cleaved surfaces and three different f-c hybridization configurations, with additional microscopic insight provided by DMFT, reveal f participation in the Fermi surface at temperatures much higher than the lattice coherence temperature, [Formula: see text] K, commonly believed to be the onset for such behavior. The DMFT results show the role of crystalline electric-field (CEF) splittings in this behavior and a T-dependent CEF degeneracy crossover below [Formula: see text] is specifically highlighted. A recent ARPES report of low T Luttinger theorem failure for CeCoIn5 is shown to be unjustified by current ARPES data and is not found in the theory.
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5
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Pal S, Wetli C, Zamani F, Stockert O, Löhneysen HV, Fiebig M, Kroha J. Fermi Volume Evolution and Crystal-Field Excitations in Heavy-Fermion Compounds Probed by Time-Domain Terahertz Spectroscopy. PHYSICAL REVIEW LETTERS 2019; 122:096401. [PMID: 30932511 DOI: 10.1103/physrevlett.122.096401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2018] [Revised: 12/23/2018] [Indexed: 06/09/2023]
Abstract
We measure the quasiparticle weight in the heavy-fermion compound CeCu_{6-x}Au_{x} (x=0, 0.1) by time-resolved terahertz spectroscopy for temperatures from 2 up to 300 K. This method distinguishes contributions from the heavy Kondo band and from the crystal-electric-field satellite bands by different terahertz response delay times. We find that the formation of heavy bands is controlled by an exponentially enhanced, high-energy Kondo scale once the crystal-electric-field states become thermally occupied. We corroborate these observations by temperature-dependent dynamical mean-field calculations for the multiorbital Anderson lattice model and discuss consequences for quantum-critical scenarios.
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Affiliation(s)
- S Pal
- Department of Materials, ETH Zürich, 8093 Zürich, Switzerland
| | - C Wetli
- Department of Materials, ETH Zürich, 8093 Zürich, Switzerland
| | - F Zamani
- Physikalisches Institut and Bethe Center for Theoretical Physics, Universität Bonn, Nussallee 12, 53115 Bonn, Germany
| | - O Stockert
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
| | - H V Löhneysen
- Institut für Festkörperphysik and Physikalisches Institut, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany
| | - M Fiebig
- Department of Materials, ETH Zürich, 8093 Zürich, Switzerland
| | - J Kroha
- Physikalisches Institut and Bethe Center for Theoretical Physics, Universität Bonn, Nussallee 12, 53115 Bonn, Germany
- Center for Correlated Matter, Zhejiang University, Hangzhou, Zhejiang 310058, China
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6
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ARPES view on surface and bulk hybridization phenomena in the antiferromagnetic Kondo lattice CeRh2Si2. Nat Commun 2016; 7:11029. [PMID: 26987899 PMCID: PMC4802051 DOI: 10.1038/ncomms11029] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2015] [Accepted: 02/12/2016] [Indexed: 11/29/2022] Open
Abstract
The hybridization between localized 4f electrons and itinerant electrons in rare-earth-based materials gives rise to their exotic properties like valence fluctuations, Kondo behaviour, heavy-fermions, or unconventional superconductivity. Here we present an angle-resolved photoemission spectroscopy (ARPES) study of the Kondo lattice antiferromagnet CeRh2Si2, where the surface and bulk Ce-4f spectral responses were clearly resolved. The pronounced 4f 0 peak seen for the Ce terminated surface gets strongly suppressed in the bulk Ce-4f spectra taken from a Si-terminated crystal due to much larger f-d hybridization. Most interestingly, the bulk Ce-4f spectra reveal a fine structure near the Fermi edge reflecting the crystal electric field splitting of the bulk magnetic 4f 15/2 state. This structure presents a clear dispersion upon crossing valence states, providing direct evidence of f-d hybridization. Our findings give precise insight into f-d hybridization penomena and highlight their importance in the antiferromagnetic phases of Kondo lattices. In rare-earth intermetallics, interaction between localized 4f electrons and itinerant electrons can result in exotic states of matter. Here, the authors use photoemission spectroscopy to reveal and study this interaction in the bulk and at the surface of the Kondo lattice antiferromagnet CeRh2Si2.
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7
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Patil S, Generalov A, Omar A. The unexpected absence of Kondo resonance in the photoemission spectrum of CeAl2. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2013; 25:382205. [PMID: 23995018 DOI: 10.1088/0953-8984/25/38/382205] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We study the temperature dependent Ce 4f spectral evolution of a well known Kondo system, CeAl2, for a range extending beyond 2 eV below the Fermi level, using photoemission spectroscopy. Interestingly, the spectral evolution is inconsistent with the predictions of the many-body spectral function calculations corresponding to the Kondo resonance interpretation of the screened Ce 4f photoemission features. In order to explain our spectral evolution we propose the phenomenon of collapse of the Kondo singlet wavefunction upon photoelectron kinetic energy measurement. Our proposal suggests that the screened final states in photoemission spectroscopy are not quantum states.
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Affiliation(s)
- S Patil
- Institut für Festkörperphysik, Technische Universität Dresden, D-01062 Dresden, Germany.
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8
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Park WK, Tobash PH, Ronning F, Bauer ED, Sarrao JL, Thompson JD, Greene LH. Observation of the hybridization gap and Fano resonance in the Kondo lattice URu2Si2. PHYSICAL REVIEW LETTERS 2012; 108:246403. [PMID: 23004299 DOI: 10.1103/physrevlett.108.246403] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2012] [Indexed: 06/01/2023]
Abstract
The nature of the second-order phase transition that occurs in URu2Si2 at 17.5 K remains puzzling despite intensive research. A key question emerging in the field is whether a hybridization gap between the renormalized bands can be identified as the "hidden" order parameter. We report on the measurement of a hybridization gap in URu2Si2 employing a spectroscopic technique based on quasiparticle scattering. The differential conductance exhibits an asymmetric double-peak structure, a clear signature for a Fano resonance in a Kondo lattice. The hybridization gap opens well above 17.5 K, indicating that it is not the hidden order parameter. Our results put stringent constraints on the origin of the hidden order transition in URu2Si2 and demonstrate that quasiparticle scattering spectroscopy can probe the band renormalizations in a Kondo lattice via detection of a novel type of Fano resonance.
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Affiliation(s)
- W K Park
- Department of Physics and the Frederick Seitz Material Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
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9
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Korytár R, Lorente N. Multi-orbital non-crossing approximation from maximally localized Wannier functions: the Kondo signature of copper phthalocyanine on Ag(100). JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:355009. [PMID: 21849718 DOI: 10.1088/0953-8984/23/35/355009] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We have developed a multi-orbital approach to compute the electronic structure of a quantum impurity using the non-crossing approximation. The calculation starts with a mean-field evaluation of the system's electronic structure using a standard quantum chemistry code; here we use density functional theory (DFT). We transformed the one-electron structure into an impurity Hamiltonian by using maximally localized Wannier functions. Hence, we have developed a method to study the Kondo effect in systems based on an initial one-electron calculation. We have applied our methodology to a copper phthalocyanine molecule chemisorbed on Ag(100), and we have described its spectral function for three different cases where the molecule presents a single spin or two spins with ferro- and anti-ferromagnetic exchange couplings. We find that the use of broken-symmetry mean-field theories such as Kohn-Sham DFT cannot deal with the complexity of the spin of open-shell molecules on metal surfaces and extra modeling is needed.
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Affiliation(s)
- Richard Korytár
- Centro de investigación en nanociencia y nanotecnología (CSIC-ICN), Campus de la UAB, E-08193 Bellaterra, Spain.
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10
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Klein M, Nuber A, Schwab H, Albers C, Tobita N, Higashiguchi M, Jiang J, Fukuda S, Tanaka K, Shimada K, Mulazzi M, Assaad FF, Reinert F. Coherent heavy quasiparticles in a CePt5 surface alloy. PHYSICAL REVIEW LETTERS 2011; 106:186407. [PMID: 21635113 DOI: 10.1103/physrevlett.106.186407] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2010] [Revised: 04/01/2011] [Indexed: 05/30/2023]
Abstract
We report on the results of a high-resolution angle-resolved photoemission study on the ordered surface alloy CePt(5). The temperature dependence of the spectra show the formation of the coherent low-energy heavy-fermion band near the Fermi level. These experimental data are supported by a multiband model calculation in the framework of the dynamical mean-field theory.
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Affiliation(s)
- M Klein
- Universität Würzburg, Experimentelle Physik VII & Röntgen Research Center for Complex Materials RCCM, Germany
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11
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Kroha J, Klein M, Nuber A, Reinert F, Stockert O, v Löhneysen H. High-temperature signatures of quantum criticality in heavy-fermion systems. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:164203. [PMID: 21386409 DOI: 10.1088/0953-8984/22/16/164203] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We propose a new criterion for distinguishing the Hertz-Millis (HM) and the local quantum critical (LQC) mechanism in heavy-fermion systems with a magnetic quantum phase transition (QPT). The criterion is based on our finding that the complete spin screening of Kondo ions can be suppressed by the Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling to the surrounding magnetic ions even without magnetic ordering and that, consequently, the signature of this suppression can be observed in spectroscopic measurements above the magnetic ordering temperature. We apply the criterion to high-resolution photoemission measurements on CeCu(6 - x)Au(x) and conclude that the QPT in this system is dominated by the LQC scenario.
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Affiliation(s)
- J Kroha
- Physikalisches Institut and Bethe Center for Theoretical Physics, Universität Bonn, Nussallee 12, 53115 Bonn, Germany.
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12
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Holder MG, Jesche A, Lombardo P, Hayn R, Vyalikh DV, Danzenbächer S, Kummer K, Krellner C, Geibel C, Kucherenko Y, Kim TK, Follath R, Molodtsov SL, Laubschat C. CeFePO: f-d hybridization and quenching of superconductivity. PHYSICAL REVIEW LETTERS 2010; 104:096402. [PMID: 20366999 DOI: 10.1103/physrevlett.104.096402] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2009] [Indexed: 05/29/2023]
Abstract
As a homologue to the new, Fe-based type of high-temperature superconductors, the electronic structure of the heavy-fermion compound CeFePO was studied by means of angle-resolved resonant photoemission. It was experimentally found-and later on confirmed by local-density approximation (LDA) as well as dynamical mean-field theory (DMFT) calculations-that the Ce 4f states hybridize to the Fe 3d states of d{3z{2}-r{2}} symmetry near the Fermi level that discloses their participation in the occurring electron-correlation phenomena and provides insight into mechanism of superconductivity in oxopnictides.
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Affiliation(s)
- M G Holder
- Institut für Festkörperphysik, Technische Universität Dresden, D-01062 Dresden, Germany
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13
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Vyalikh DV, Danzenbächer S, Kucherenko Y, Krellner C, Geibel C, Laubschat C, Shi M, Patthey L, Follath R, Molodtsov SL. Tuning the hybridization at the surface of a heavy-fermion system. PHYSICAL REVIEW LETTERS 2009; 103:137601. [PMID: 19905540 DOI: 10.1103/physrevlett.103.137601] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2009] [Indexed: 05/28/2023]
Abstract
Electron-hybridization phenomena in YbRh_{2}Si_{2} were probed by angle-resolved photoemission. It was shown that the Yb 4f-Rh 4d hybridization strength in the surface region of this heavy-fermion material can be varied by deposition of Ag. Site-specific charge transfer from adatoms leads to change of the energy overlap of the interacting states close to the Fermi energy. Our study demonstrates a new way to tune the hybridization between 4f and valence electrons as well as the induced strong correlation effects at the surface of heavy-fermion systems.
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Affiliation(s)
- D V Vyalikh
- Institut für Festkörperphysik, Technische Universität Dresden, D-01062 Dresden, Germany.
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14
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Park WK, Greene LH. Andreev reflection and order parameter symmetry in heavy-fermion superconductors: the case of CeCoIn(5). JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2009; 21:103203. [PMID: 21817420 DOI: 10.1088/0953-8984/21/10/103203] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We review the current status of Andreev reflection spectroscopy on the heavy fermions, mostly focusing on the case of CeCoIn(5), a heavy-fermion superconductor with a critical temperature of 2.3 K. This is a well-established technique to investigate superconducting order parameters via measurements of the differential conductance from nanoscale metallic junctions. Andreev reflection is clearly observed in CeCoIn(5) as in other heavy-fermion superconductors. Considering the large mismatch in Fermi velocities, this observation seemingly appears to disagree with the Blonder-Tinkham-Klapwijk (BTK) theory. The measured Andreev signal is highly reduced to the order of maximum ∼13% compared to the theoretically predicted value (100%). The background conductance exhibits a systematic evolution in its asymmetry over a wide temperature range from above the heavy-fermion coherence temperature down to well below the superconducting transition temperature. Analysis of the conductance spectra using the extended BTK model provides a qualitative measure for the superconducting order parameter symmetry, which is determined to be the d(x(2)-y(2)) wave in CeCoIn(5). It is found that existing models do not quantitatively account for the data, which we attribute to the intrinsic properties of the heavy fermions. A substantial body of experimental data and extensive theoretical analysis point to the existence of two-fluid components in CeCoIn(5) and other heavy-fermion compounds. A phenomenological model is proposed employing a Fano interference effect between two conductance channels in order to explain both the conductance asymmetry and the reduced Andreev signal. This model appears plausible not only because it provides good fits to the data but also because it is highly likely that the electrical conduction occurs via two channels, one into the heavy-electron liquid and the other into the conduction electron continuum. Further experimental and theoretical investigations will shed new light on the mechanism of how the coherent heavy-electron liquid emerges out of the Kondo lattice, a prototypical strongly correlated electron system. Unresolved issues and future directions are also discussed.
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Affiliation(s)
- W K Park
- Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
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15
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Klein M, Nuber A, Reinert F, Kroha J, Stockert O, van Löhneysen H. Signature of quantum criticality in photoemission spectroscopy. PHYSICAL REVIEW LETTERS 2008; 101:266404. [PMID: 19437657 DOI: 10.1103/physrevlett.101.266404] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
A quantum phase transition in a heavy-fermion compound may destroy the Fermi-liquid ground state. However, the conditions for this breakdown have remained obscure. We report the first direct investigation of heavy quasiparticle formation and breakdown in the canonical system CeCu(6-x)Au(x) by ultraviolet photoemission spectroscopy at elevated temperatures without the complications of lattice coherence. Surprisingly, the single-ion Kondo energy scale T(K) exhibits an abrupt step near the quantum critical Au concentration of x(c) = 0.1. We show theoretically that this step is expected from a highly nonlinear renormalization of the local spin coupling at each Ce site, induced by spin fluctuations on neighboring sites. It provides a general high-temperature indicator for heavy-fermion quasiparticle breakdown at a quantum phase transition.
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Affiliation(s)
- M Klein
- Universitüt Würzburg, Experimentelle Physik II, Am Hubland, D-97074 Würzburg, Germany
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16
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Danzenbächer S, Kucherenko Y, Laubschat C, Vyalikh DV, Hossain Z, Geibel C, Zhou XJ, Yang WL, Mannella N, Hussain Z, Shen ZX, Molodtsov SL. Energy dispersion of 4f-derived emissions in photoelectron spectra of the heavy-fermion compound YbIr2Si2. PHYSICAL REVIEW LETTERS 2006; 96:106402. [PMID: 16605769 DOI: 10.1103/physrevlett.96.106402] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2005] [Indexed: 05/08/2023]
Abstract
Angle-resolved photoemission spectra of the heavy-fermion system YbIr(2)Si(2) are reported that reveal strong momentum (k) dependent splittings of the 4f(13) bulk and surface emissions around the expected intersection points of the 4f final states with valence bands in the Brillouin zone. The obtained dispersion is explained in terms of a simplified periodic Anderson model by a k dependence of the electron hopping matrix element disregarding clearly interpretation in terms of a single-impurity model.
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Affiliation(s)
- S Danzenbächer
- Institut für Festkörperphysik, Technische Universität Dresden, D-01062 Dresden, Germany
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17
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Shimoyamada A, Tsuda S, Ishizaka K, Kiss T, Shimojima T, Togashi T, Watanabe S, Zhang CQ, Chen CT, Matsushita Y, Ueda H, Ueda Y, Shin S. Heavy-fermion-like state in a transition metal oxide LiV2O4 single crystal: indication of Kondo resonance in the photoemission spectrum. PHYSICAL REVIEW LETTERS 2006; 96:026403. [PMID: 16486605 DOI: 10.1103/physrevlett.96.026403] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/10/2005] [Indexed: 05/06/2023]
Abstract
We have performed a vacuum ultraviolet laser excited photoemission spectroscopy on a d-electron heavy-fermion-like material LiV2O4 single crystal. We observed a sharp peak structure in the density of states at approximately 4 meV above the Fermi level (E(F)). The evolution of the peak height corresponds well with the crossover behavior to the heavy-fermion-like state as observed in the thermal and transport properties. The position, shape, and temperature (T) dependence of the peak structure is quite similar to the Kondo resonance observed in conventional f-electron heavy Fermion compounds.
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Affiliation(s)
- A Shimoyamada
- Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
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18
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Unconventional Superconductivity and Magnetism in Lanthanide and Actinide Intermetallic Compounds. ACTA ACUST UNITED AC 2004. [DOI: 10.1016/s0168-1273(04)34002-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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19
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Souma S, Machida Y, Sato T, Takahashi T, Matsui H, Wang SC, Ding H, Kaminski A, Campuzano JC, Sasaki S, Kadowaki K. The origin of multiple superconducting gaps in MgB2. Nature 2003; 423:65-7. [PMID: 12721624 DOI: 10.1038/nature01619] [Citation(s) in RCA: 204] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2003] [Accepted: 04/08/2003] [Indexed: 11/09/2022]
Abstract
Magnesium diboride, MgB2, has the highest transition temperature (T(c) = 39 K) of the known metallic superconductors. Whether the anomalously high T(c) can be described within the conventional BCS (Bardeen-Cooper-Schrieffer) framework has been debated. The key to understanding superconductivity lies with the 'superconducting energy gap' associated with the formation of the superconducting pairs. Recently, the existence of two kinds of superconducting gaps in MgB2 has been suggested by several experiments; this is in contrast to both conventional and high-T(c) superconductors. A clear demonstration of two gaps has not yet been made because the previous experiments lacked the ability to resolve the momentum of the superconducting electrons. Here we report direct experimental evidence for the two-band superconductivity in MgB2, by separately observing the superconducting gaps of the sigma and pi bands (as well as a surface band). The gaps have distinctly different sizes, which unambiguously establishes MgB2 as a two-gap superconductor.
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Affiliation(s)
- S Souma
- Department of Physics, Tohoku University, Sendai 980-8578, Japan
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Valla T, Johnson PD, Yusof Z, Wells B, Li Q, Loureiro SM, Cava RJ, Mikami M, Mori Y, Yoshimura M, Sasaki T. Coherence incoherence and dimensional crossover in layered strongly correlated metals. Nature 2002; 417:627-30. [PMID: 12050659 DOI: 10.1038/nature00774] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The properties of an interacting electron system depend on the electron correlations and the effective dimensionality. For example, Coulomb repulsion between electrons may inhibit, or completely block, conduction by intersite electron hopping, thereby determining whether a material is a metal or an insulator. Furthermore, correlation effects increase as the number of effective dimensions decreases; in three-dimensional systems, the low-energy electronic states behave as quasiparticles, whereas in one-dimensional systems, even weak interactions break the quasiparticles into collective excitations. Dimensionality is particularly important for exotic low-dimensional materials where one- or two-dimensional building blocks are loosely connected into a three-dimensional whole. Here we examine two such layered metallic systems with angle-resolved photoemission spectroscopy and electronic transport measurements, and we find a crossover in the number of effective dimensions from two to three with decreasing temperature. This is apparent from the observation that, in the direction perpendicular to the layers, the materials have an insulating character at high temperatures but become metal-like at low temperatures, whereas transport within the layers remains metallic over the whole temperature range. We propose that this change in effective dimensionality correlates with the presence of coherent quasiparticles within the layers.
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Affiliation(s)
- T Valla
- Physics Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
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