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Fumega AO, Lado JL. Nature of the Unconventional Heavy-Fermion Kondo State in Monolayer CeSiI. NANO LETTERS 2024; 24:4272-4278. [PMID: 38394370 PMCID: PMC11010227 DOI: 10.1021/acs.nanolett.4c00619] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2024] [Revised: 02/14/2024] [Accepted: 02/15/2024] [Indexed: 02/25/2024]
Abstract
CeSiI has been recently isolated in the ultrathin limit, establishing CeSiI as the first intrinsic two-dimensional van der Waals heavy-fermion material up to 85 K. We show that, due to the strong spin-orbit coupling, the local moments develop a multipolar real-space magnetic texture, leading to local pseudospins with a nearly vanishing net moment. To elucidate its Kondo-screened regime, we extract from first-principles the parameters of the Kondo lattice model describing this material. We develop a pseudofermion methodology in combination with ab initio calculations to reveal the nature of the heavy-fermion state in CeSiI. We analyze the competing magnetic interactions leading to an unconventional heavy-fermion order as a function of the magnetic exchange between the localized f-electrons and the strength of the Kondo coupling. Our results show that the magnetic exchange interactions promote an unconventional momentum-dependent Kondo-screened phase, establishing the nature of the heavy-fermion state observed in CeSiI.
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Affiliation(s)
- Adolfo O. Fumega
- Department of Applied
Physics, Aalto University, 02150 Espoo, Finland
| | - Jose L. Lado
- Department of Applied
Physics, Aalto University, 02150 Espoo, Finland
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2
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Anisotropy-driven quantum criticality in an intermediate valence system. Nat Commun 2022; 13:2141. [PMID: 35440657 PMCID: PMC9019086 DOI: 10.1038/s41467-022-29757-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2019] [Accepted: 03/29/2022] [Indexed: 11/08/2022] Open
Abstract
Intermetallic compounds containing f-electron elements have been prototypical materials for investigating strong electron correlations and quantum criticality (QC). Their heavy fermion ground state evoked by the magnetic f-electrons is susceptible to the onset of quantum phases, such as magnetism or superconductivity, due to the enhanced effective mass (m*) and a corresponding decrease of the Fermi temperature. However, the presence of f-electron valence fluctuations to a non-magnetic state is regarded an anathema to QC, as it usually generates a paramagnetic Fermi-liquid state with quasiparticles of moderate m*. Such systems are typically isotropic, with a characteristic energy scale T0 of the order of hundreds of kelvins that require large magnetic fields or pressures to promote a valence or magnetic instability. Here we show the discovery of a quantum critical behaviour and a Lifshitz transition under low magnetic field in an intermediate valence compound α-YbAlB4. The QC origin is attributed to the anisotropic hybridization between the conduction and localized f-electrons. These findings suggest a new route to bypass the large valence energy scale in developing the QC. The nature of quantum criticality in intermetallic f-electron compounds exhibiting valence fluctuations is not well understood. Here, using a combination of experimental techniques, the authors attribute quantum criticality in YbAlB4 to the anisotropic hybridization between the conduction and f-electrons.
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Shimura Y, Wörl A, Sundermann M, Tsuda S, Adroja DT, Bhattacharyya A, Strydom AM, Hillier AD, Pratt FL, Gloskovskii A, Severing A, Onimaru T, Gegenwart P, Takabatake T. Antiferromagnetic Correlations in Strongly Valence Fluctuating CeIrSn. PHYSICAL REVIEW LETTERS 2021; 126:217202. [PMID: 34114835 DOI: 10.1103/physrevlett.126.217202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2020] [Accepted: 04/29/2021] [Indexed: 06/12/2023]
Abstract
CeIrSn with a quasikagome Ce lattice in the hexagonal basal plane is a strongly valence fluctuating compound, as we confirm by hard x-ray photoelectron spectroscopy and inelastic neutron scattering, with a high Kondo temperature of T_{K}∼480 K. We report a negative in-plane thermal expansion α/T below 2 K, which passes through a broad minimum near 0.75 K. Volume and a-axis magnetostriction for B∥a are markedly negative at low fields and change sign before a sharp metamagnetic anomaly at 6 T. These behaviors are unexpected for Ce-based intermediate valence systems, which should feature positive expansivity. Rather they point towards antiferromagnetic correlations at very low temperatures. This is supported by muon spin relaxation measurements down to 0.1 K, which provide microscopic evidence for a broad distribution of internal magnetic fields. Comparison with isostructural CeRhSn suggests that these antiferromagnetic correlations emerging at T≪T_{K} result from geometrical frustration.
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Affiliation(s)
- Y Shimura
- Graduate School of Advanced Science and Engineering, Hiroshima University, Higashi-Hiroshima 739-8530, Japan
| | - A Wörl
- Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
| | - M Sundermann
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
- Deutsches Elektronen-Synchrotron DESY, 22607 Hamburg, Germany
| | - S Tsuda
- Graduate School of Advanced Science and Engineering, Hiroshima University, Higashi-Hiroshima 739-8530, Japan
| | - D T Adroja
- ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot Oxon OX11 0QX, United Kingdom
- Highly Correlated Matter Research Group, Physics Department, University of Johannesburg, PO Box 524, Auckland Park 2006, South Africa
| | - A Bhattacharyya
- Department of Physics, Ramakrishna Mission Vivekananda Educational and Research Institute, Belur Math, Howrah 711202, West Bengal, India
| | - A M Strydom
- Highly Correlated Matter Research Group, Physics Department, University of Johannesburg, PO Box 524, Auckland Park 2006, South Africa
| | - A D Hillier
- ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot Oxon OX11 0QX, United Kingdom
| | - F L Pratt
- ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot Oxon OX11 0QX, United Kingdom
| | - A Gloskovskii
- Deutsches Elektronen-Synchrotron DESY, 22607 Hamburg, Germany
| | - A Severing
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
- Institute of Physics II, University of Cologne, 50937 Cologne, Germany
| | - T Onimaru
- Graduate School of Advanced Science and Engineering, Hiroshima University, Higashi-Hiroshima 739-8530, Japan
| | - P Gegenwart
- Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
| | - T Takabatake
- Graduate School of Advanced Science and Engineering, Hiroshima University, Higashi-Hiroshima 739-8530, Japan
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Magnon Bose-Einstein condensation and superconductivity in a frustrated Kondo lattice. Proc Natl Acad Sci U S A 2020; 117:20462-20467. [PMID: 32788363 DOI: 10.1073/pnas.2000501117] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Motivated by recent experiments on magnetically frustrated heavy fermion metals, we theoretically study the phase diagram of the Kondo lattice model with a nonmagnetic valence bond solid ground state on a ladder. A similar physical setting may be naturally occurring in [Formula: see text], [Formula: see text], and [Formula: see text] compounds. In the insulating limit, the application of a magnetic field drives a quantum phase transition to an easy-plane antiferromagnet, which is described by a Bose-Einstein condensation of magnons. Using a combination of field theoretical techniques and density matrix renormalization group calculations we demonstrate that in one dimension this transition is stable in the presence of a metallic Fermi sea, and its universality class in the local magnetic response is unaffected by the itinerant gapless fermions. Moreover, we find that fluctuations about the valence bond solid ground state can mediate an attractive interaction that drives unconventional superconducting correlations. We discuss the extensions of our findings to higher dimensions and argue that depending on the filling of conduction electrons, the magnon Bose-Einstein condensation transition can remain stable in a metal also in dimensions two and three.
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Mao Z, Xue K, Zhang Y, Zhang J, Tang L, Chen X. Strain-induced magnetic moment enhancement in frustrated antiferromagnet Cs 2CuBr 4. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:365801. [PMID: 32353834 DOI: 10.1088/1361-648x/ab8ecb] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2020] [Accepted: 04/30/2020] [Indexed: 06/11/2023]
Abstract
The structure and magnetic properties are studied in co-doped Cs2-xKxCuBr4-xClxand pressurized Cs2CuBr4samples. No structural phase transition is found with doping concentrationx⩽ 0.1 and pre-compression pressure up to 4.5 GPa. The maximum susceptibility temperatureTmaxof the zero-field-cooling (ZFC) susceptibility curves decreases slightly with increasing doping concentration and pre-compression pressure, indicating only small changes in the exchange coupling constants. However, an unusual enhancement of the magnetic moment deduced from the ZFC susceptibility is observed in both series samples. A maximum increase of 40% is obtained in Cs1.9K0.1CuBr3.9Cl0.1sample. The magnetic moment increases almost linearly with decreasing Δ, i.e., defined as the wavenumber difference between the short- and long-bond stretching modes of the CuBr42-tetrahedra in the Raman spectra. The effect is likely due to the recovery of the Cu-3d orbital magnetic moments by strain-induced suppression of Jahn-Teller distortion in CuBr42-tetrahedra.
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Affiliation(s)
- Zhongquan Mao
- School of Physics and Optics, South China University of Technology, Guangzhou, People's Republic of China
| | - Kaiyuan Xue
- School of Physics and Optics, South China University of Technology, Guangzhou, People's Republic of China
| | - Yang Zhang
- Center for High Pressure Science (CHiPS), State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao, People's Republic of China
| | - Jiang Zhang
- School of Physics and Optics, South China University of Technology, Guangzhou, People's Republic of China
| | - Lingyun Tang
- School of Physics and Optics, South China University of Technology, Guangzhou, People's Republic of China
| | - Xi Chen
- School of Physics and Optics, South China University of Technology, Guangzhou, People's Republic of China
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Lucas S, Grube K, Huang CL, Sakai A, Wunderlich S, Green EL, Wosnitza J, Fritsch V, Gegenwart P, Stockert O, V Löhneysen H. Entropy Evolution in the Magnetic Phases of Partially Frustrated CePdAl. PHYSICAL REVIEW LETTERS 2017; 118:107204. [PMID: 28339268 DOI: 10.1103/physrevlett.118.107204] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2016] [Indexed: 06/06/2023]
Abstract
In the heavy-fermion metal CePdAl, long-range antiferromagnetic order coexists with geometric frustration of one-third of the Ce moments. At low temperatures, the Kondo effect tends to screen the frustrated moments. We use magnetic fields B to suppress the Kondo screening and study the magnetic phase diagram and the evolution of the entropy with B employing thermodynamic probes. We estimate the frustration by introducing a definition of the frustration parameter based on the enhanced entropy, a fundamental feature of frustrated systems. In the field range where the Kondo screening is suppressed, the liberated moments tend to maximize the magnetic entropy and strongly enhance the frustration. Based on our experiments, this field range may be a promising candidate to search for a quantum spin liquid.
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Affiliation(s)
- S Lucas
- Max-Planck-Institut für Chemische Physik fester Stoffe, 01187 Dresden, Germany
- Institut für Festkörperphysik, TU Dresden, 01062 Dresden, Germany
| | - K Grube
- Institut für Festkörperphysik, Karlsruher Institut für Technologie, 76131 Karlsruhe, Germany
| | - C-L Huang
- Max-Planck-Institut für Chemische Physik fester Stoffe, 01187 Dresden, Germany
- Institut für Festkörperphysik, Karlsruher Institut für Technologie, 76131 Karlsruhe, Germany
- Physikalisches Institut, Karlsruher Institut für Technologie, 76049 Karlsruhe, Germany
| | - A Sakai
- Experimentalphysik VI, Elektronische Korrelationen und Magnetismus, Universität Augsburg, 86159 Augsburg, Germany
| | - S Wunderlich
- Max-Planck-Institut für Chemische Physik fester Stoffe, 01187 Dresden, Germany
| | - E L Green
- Hochfeld-Magnetlabor Dresden (EMFL-HLD), Helmholtz-Zentrum Dresden-Rossendorf, 01314 Dresden, Germany
| | - J Wosnitza
- Institut für Festkörperphysik, TU Dresden, 01062 Dresden, Germany
- Hochfeld-Magnetlabor Dresden (EMFL-HLD), Helmholtz-Zentrum Dresden-Rossendorf, 01314 Dresden, Germany
| | - V Fritsch
- Experimentalphysik VI, Elektronische Korrelationen und Magnetismus, Universität Augsburg, 86159 Augsburg, Germany
| | - P Gegenwart
- Experimentalphysik VI, Elektronische Korrelationen und Magnetismus, Universität Augsburg, 86159 Augsburg, Germany
| | - O Stockert
- Max-Planck-Institut für Chemische Physik fester Stoffe, 01187 Dresden, Germany
| | - H V Löhneysen
- Institut für Festkörperphysik, Karlsruher Institut für Technologie, 76131 Karlsruhe, Germany
- Physikalisches Institut, Karlsruher Institut für Technologie, 76049 Karlsruhe, Germany
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Gegenwart P. Grüneisen parameter studies on heavy fermion quantum criticality. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2016; 79:114502. [PMID: 27710924 DOI: 10.1088/0034-4885/79/11/114502] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The Grüneisen parameter, experimentally determined from the ratio of thermal expansion to specific heat, quantifies the pressure dependence of characteristic energy scales of matter. It is highly enhanced for Kondo lattice systems, whose properties are strongly dependent on the pressure sensitive antiferromagnetic exchange interaction between f- and conduction electrons. In this review, we focus on the divergence of the Grüneisen parameter and its magnetic analogue, the adiabatic magnetocaloric effect, for heavy-fermion metals near quantum critical points. We compare experimental results with current theoretical models, including the effect of strong geometrical frustration. We also discuss the possibility of using materials with the divergent magnetic Grüneisen parameter for adiabatic demagnetization cooling to very low temperatures.
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Affiliation(s)
- Philipp Gegenwart
- EP VI, Center for Electronic Correlations and Magnetism, Institute of Physics, Augsburg University, 86159 Augsburg, Germany
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Küchler R, Stingl C, Gegenwart P. A uniaxial stress capacitive dilatometer for high-resolution thermal expansion and magnetostriction under multiextreme conditions. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2016; 87:073903. [PMID: 27475567 DOI: 10.1063/1.4958957] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Thermal expansion and magnetostriction are directional dependent thermodynamic quantities. For the characterization of novel quantum phases of matter, it is required to study materials under multi-extreme conditions, in particular, down to very low temperatures, in very high magnetic fields or under high pressure. We developed a miniaturized capacitive dilatometer suitable for temperatures down to 20 mK and usage in high magnetic fields, which exerts a large spring force between 40 to 75 N on the sample. This corresponds to a uniaxial stress up to 3 kbar for a sample with cross section of (0.5 mm)(2). We describe design and performance test of the dilatometer which resolves length changes with high resolution of 0.02 Å at low temperatures. The miniaturized device can be utilized in any standard cryostat, including dilution refrigerators or the commercial physical property measurement system.
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Affiliation(s)
- R Küchler
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
| | - C Stingl
- Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, Universitätsstrasse 2, 86135 Augsburg, Germany
| | - P Gegenwart
- Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, Universitätsstrasse 2, 86135 Augsburg, Germany
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