1
|
Lavroff RH, Munarriz J, Dickerson CE, Munoz F, Alexandrova AN. Chemical bonding dictates drastic critical temperature difference in two seemingly identical superconductors. Proc Natl Acad Sci U S A 2024; 121:e2316101121. [PMID: 38547068 PMCID: PMC10998635 DOI: 10.1073/pnas.2316101121] [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: 09/21/2023] [Accepted: 01/11/2024] [Indexed: 04/08/2024] Open
Abstract
Though YB6 and LaB6 share the same crystal structure, atomic valence electron configuration, and phonon modes, they exhibit drastically different phonon-mediated superconductivity. YB6 superconducts below 8.4 K, giving it the second-highest critical temperature of known borides, second only to MgB2. LaB6 does not superconduct until near-absolute zero temperatures (below 0.45 K), however. Though previous studies have quantified the canonical superconductivity descriptors of YB6's greater Fermi-level (Ef) density of states and higher electron-phonon coupling (EPC), the root of this difference has not been assessed with full detail of the electronic structure. Through chemical bonding, we determine low-lying, unoccupied 4f atomic orbitals in lanthanum to be the key difference between these superconductors. These orbitals, which are not accessible in YB6, hybridize with π B-B bonds and bring this π-system lower in energy than the σ B-B bonds otherwise at Ef. This inversion of bands is crucial: the optical phonon modes we show responsible for superconductivity cause the σ-orbitals of YB6 to change drastically in overlap, but couple weakly to the π-orbitals of LaB6. These phonons in YB6 even access a crossing of electronic states, indicating strong EPC. No such crossing in LaB6 is observed. Finally, a supercell (the M k-point) is shown to undergo Peierls-like effects in YB6, introducing additional EPC from both softened acoustic phonons and the same electron-coupled optical modes as in the unit cell. Overall, we find that LaB6 and YB6 have fundamentally different mechanisms of superconductivity, despite their otherwise near-identity.
Collapse
Affiliation(s)
- Robert H. Lavroff
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA90095
| | - Julen Munarriz
- Departamento de Química Física and Instituto de Biocomputación y Física de Sistemas Complejos, Universidad de Zaragoza, Zaragoza50009, Spain
| | - Claire E. Dickerson
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA90095
| | - Francisco Munoz
- Departamento de Física, Facultad de Ciencias, Universidad de Chile, Santiago7800024, Chile
- Center for the Development of Nanoscience and Nanotechnology, Santiago9330111, Chile
| | - Anastassia N. Alexandrova
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA90095
- Department of Materials Science and Engineering, University of California, Los Angeles, CA90095
- California NanoSystems Institute, University of California, Los Angeles, CA90095
| |
Collapse
|
2
|
Munarriz J, Robinson PJ, Alexandrova AN. Towards a Single Chemical Model for Understanding Lanthanide Hexaborides. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202010638] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Julen Munarriz
- Department of Chemistry and Biochemistry University of California Los Angeles Los Angeles CA 90095 USA
| | - Paul J. Robinson
- Department of Chemistry Columbia University New York NY 10027 USA
| | - Anastassia N. Alexandrova
- Department of Chemistry and Biochemistry University of California Los Angeles Los Angeles CA 90095 USA
- California NanoSystems Institute University of California Los Angeles Los Angeles CA 90095 USA
| |
Collapse
|
3
|
Munarriz J, Robinson PJ, Alexandrova AN. Towards a Single Chemical Model for Understanding Lanthanide Hexaborides. Angew Chem Int Ed Engl 2020; 59:22684-22689. [PMID: 33015915 DOI: 10.1002/anie.202010638] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2020] [Revised: 08/20/2020] [Indexed: 11/05/2022]
Abstract
Lanthanide hexaborides (LnB6 ) have disparate and often anomalous properties, from structurally homogeneous mixed valency, to superconductivity, spectral anomalies, and unexplained phase transitions. It is unclear how such a diversity of properties may arise in the solids of identical crystal structures and seemingly very similar electronic structures. Building on our previous model for SmB6 (mixed valent, with a peak in specific heat, and pressure induced magnetic phase transitions), we present a unifying dynamic bonding model for LnB6 that explains simultaneously EuB6 (possessing an anomalous peak in specific heat at low T, magnetic phase transitions, and no mixed valency), YbB6 (mixed valent topological insulator), and rather ordinary LaB6 . We show that Ln can engage in covalent bonding with boron, and, in some members of the LnB6 family, also easily access alternative bonding states through the electron-phonon coupling. The accessibility, relative energetics, and bonding nature of the states involved dictate the properties.
Collapse
Affiliation(s)
- Julen Munarriz
- Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, CA, 90095, USA
| | - Paul J Robinson
- Department of Chemistry, Columbia University, New York, NY, 10027, USA
| | - Anastassia N Alexandrova
- Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, CA, 90095, USA.,California NanoSystems Institute, University of California Los Angeles, Los Angeles, CA, 90095, USA
| |
Collapse
|
4
|
Robinson PJ, Munarriz J, Valentine ME, Granmoe A, Drichko N, Chamorro JR, Rosa PF, McQueen TM, Alexandrova AN. Dynamical Bonding Driving Mixed Valency in a Metal Boride. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202000945] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Paul J. Robinson
- Department of Chemistry and Biochemistry University of California Los Angeles Los Angeles CA 90095 USA
- Current Address: Department of Chemistry Columbia University New York NY 10027 USA
| | - Julen Munarriz
- Department of Chemistry and Biochemistry University of California Los Angeles Los Angeles CA 90095 USA
| | - Michael E. Valentine
- Institute for Quantum Matter Department of Physics and Astronomy The Johns Hopkins University Baltimore MD 21218 USA
| | - Austin Granmoe
- Institute for Quantum Matter Department of Physics and Astronomy The Johns Hopkins University Baltimore MD 21218 USA
| | - Natalia Drichko
- Institute for Quantum Matter Department of Physics and Astronomy The Johns Hopkins University Baltimore MD 21218 USA
| | - Juan R. Chamorro
- Institute for Quantum Matter Department of Physics and Astronomy The Johns Hopkins University Baltimore MD 21218 USA
- Department of Chemistry The Johns Hopkins University Baltimore MD 21218 USA
| | | | - Tyrel M. McQueen
- Institute for Quantum Matter Department of Physics and Astronomy The Johns Hopkins University Baltimore MD 21218 USA
- Department of Chemistry The Johns Hopkins University Baltimore MD 21218 USA
- Department of Materials Science and Engineering The Johns Hopkins University Baltimore MD 21218 USA
| | - Anastassia N. Alexandrova
- Department of Chemistry and Biochemistry University of California Los Angeles Los Angeles CA 90095 USA
- California NanoSystems Institute Los Angeles CA 90095 USA
| |
Collapse
|
5
|
Robinson PJ, Munarriz J, Valentine ME, Granmoe A, Drichko N, Chamorro JR, Rosa PF, McQueen TM, Alexandrova AN. Dynamical Bonding Driving Mixed Valency in a Metal Boride. Angew Chem Int Ed Engl 2020; 59:10996-11002. [PMID: 32202032 DOI: 10.1002/anie.202000945] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2020] [Indexed: 11/08/2022]
Abstract
Samarium hexaboride is an anomaly, having many exotic and seemingly mutually incompatible properties. It was proposed to be a mixed-valent semiconductor, and later a topological Kondo insulator, and yet has a Fermi surface despite being an insulator. We propose a new and unified understanding of SmB6 centered on the hitherto unrecognized dynamical bonding effect: the coexistence of two Sm-B bonding modes within SmB6 , corresponding to different oxidation states of the Sm. The mixed valency arises in SmB6 from thermal population of these distinct minima enabled by motion of B. Our model simultaneously explains the thermal valence fluctuations, appearance of magnetic Fermi surface, excess entropy at low temperatures, pressure-induced phase transitions, and related features in Raman spectra and their unexpected dependence on temperature and boron isotope.
Collapse
Affiliation(s)
- Paul J Robinson
- Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, CA, 90095, USA.,Current Address: Department of Chemistry, Columbia University, New York, NY, 10027, USA
| | - Julen Munarriz
- Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, CA, 90095, USA
| | - Michael E Valentine
- Institute for Quantum Matter, Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD, 21218, USA
| | - Austin Granmoe
- Institute for Quantum Matter, Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD, 21218, USA
| | - Natalia Drichko
- Institute for Quantum Matter, Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD, 21218, USA
| | - Juan R Chamorro
- Institute for Quantum Matter, Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD, 21218, USA.,Department of Chemistry, The Johns Hopkins University, Baltimore, MD, 21218, USA
| | | | - Tyrel M McQueen
- Institute for Quantum Matter, Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD, 21218, USA.,Department of Chemistry, The Johns Hopkins University, Baltimore, MD, 21218, USA.,Department of Materials Science and Engineering, The Johns Hopkins University, Baltimore, MD, 21218, USA
| | - Anastassia N Alexandrova
- Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, CA, 90095, USA.,California NanoSystems Institute, Los Angeles, CA, 90095, USA
| |
Collapse
|
6
|
Zhuang JT, Zheng XJ, Wang ZY, Ming X, Li H, Liu Y, Song HF. Valence transition in topological Kondo insulator. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:035602. [PMID: 31536975 DOI: 10.1088/1361-648x/ab4625] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We investigate the valence transition in three-dimensional topological Kondo insulator through slave-boson analysis of periodic Anderson model. By including the effect of intra-atomic Coulomb correlation [Formula: see text] between conduction and local electrons, we find a first-order valence transition from Kondo region to mixed valence state upon ascending of local f- level above a critical [Formula: see text], and this valence transition usually occurs very close to or simultaneously with a topological transition. Near the parameter region of zero-temperature valence transition, rise of temperature can generate a thermal valence transition from mixed valence to Kondo region, accompanied by a first-order topological transition. Remarkably, above a critical [Formula: see text] which is considerably smaller than that generating paramagnetic valence transition, the original continuous antiferromagnetic transition is shifted to first order one, at which a discontinuous valence shift takes place. Upon increasing [Formula: see text], the paramagnetic valence transition approaches then converges with the first-order antiferromagnetic transition, leaving a significant valence shift on the magnetic boundary. The continuous antiferromagnetic transition, first-order antiferromagnetic transition, paramagnetic valence transition and topological transitions are all summarized in a global phase diagram. Our proposed exotic transition processes can help to understand the thermal valence variation as well as the valence shift around the pressure-induced magnetic transition in topological Kondo insulator candidates and in other heavy-fermion systems.
Collapse
Affiliation(s)
- Jia-Tao Zhuang
- College of Science, Guilin University of Technology, Guilin 541004, People's Republic of China
| | | | | | | | | | | | | |
Collapse
|
7
|
Li H, Zhong Y, Liu Y, Luo HG, Song HF. [Formula: see text] classification for a novel antiferromagnetic topological insulating phase in three-dimensional topological Kondo insulator. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:435601. [PMID: 30215616 DOI: 10.1088/1361-648x/aae17b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Antiferromagnetic topological insulator (AFTI) is a topological matter that breaks time-reversal symmetry. Since its proposal, explorations of AFTI in strong-correlated systems are still lacking. In this paper, we show for the first time that a novel AFTI phase can be realized in three-dimensional topological Kondo insulator (TKI). In a wide parameter region, the ground states of TKI undergo a second-order transition to antiferromagnetic insulating phases which conserve a combined symmetry of time reversal and a lattice translation, allowing us to derive a [Formula: see text]-classification formula for these states. By calculating the [Formula: see text] index, the antiferromagnetic insulating states are classified into AFTI or non-topological antiferromagnetic insulator (nAFI) in different parameter regions. On the antiferromagnetic surfaces in AFTI, we find topologically protected gapless Dirac cones inside the bulk gap, leading to metallic Fermi rings exhibiting helical spin texture with weak spin-momentum locking. Depending on model parameters, the magnetic transitions take place either between AFTI and strong topological insulator, or between nAFI and weak topological insulator. By varying some model parameters, we find a topological transition between AFTI and nAFI, driving by closing of bulk gap. Our work may account for the pressure-induced magnetism in TKI compound SmB6, and helps to explore richer AFTI phases in heavy-fermion systems as well as in other strong-correlated systems.
Collapse
Affiliation(s)
- Huan Li
- College of Science, Guilin University of Technology, Guilin 541004, People's Republic of China
| | | | | | | | | |
Collapse
|
8
|
Sundermann M, Yavaş H, Chen K, Kim DJ, Fisk Z, Kasinathan D, Haverkort MW, Thalmeier P, Severing A, Tjeng LH. 4f Crystal Field Ground State of the Strongly Correlated Topological Insulator SmB_{6}. PHYSICAL REVIEW LETTERS 2018; 120:016402. [PMID: 29350947 DOI: 10.1103/physrevlett.120.016402] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2017] [Revised: 09/25/2017] [Indexed: 06/07/2023]
Abstract
We investigated the crystal-electric field ground state of the 4f manifold in the strongly correlated topological insulator SmB_{6} using core-level nonresonant inelastic x-ray scattering. The directional dependence of the scattering function that arises from higher multipole transitions establishes unambiguously that the Γ_{8} quartet state of the Sm f^{5} J=5/2 configuration governs the ground-state symmetry and, hence, the topological properties of SmB_{6}. Our findings contradict the results of density functional calculations reported so far.
Collapse
Affiliation(s)
- M Sundermann
- Institute of Physics II, University of Cologne, Zülpicher Straße 77, 50937 Cologne, Germany
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany
| | - H Yavaş
- PETRA III, Deutsches Elektronen-Synchrotron (DESY), Notkestraße 85, 22607 Hamburg, Germany
| | - K Chen
- Institute of Physics II, University of Cologne, Zülpicher Straße 77, 50937 Cologne, Germany
| | - D J Kim
- Department of Physics and Astronomy, University of California, Irvine, California 92697, USA
| | - Z Fisk
- Department of Physics and Astronomy, University of California, Irvine, California 92697, USA
| | - D Kasinathan
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany
| | - M W Haverkort
- Institute for Theoretical Physics, Heidelberg University, Philosophenweg 19, 69120 Heidelberg, Germany
| | - P Thalmeier
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany
| | - A Severing
- Institute of Physics II, University of Cologne, Zülpicher Straße 77, 50937 Cologne, Germany
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany
| | - L H Tjeng
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany
| |
Collapse
|
9
|
Zhou Y, Wu Q, Rosa PFS, Yu R, Guo J, Yi W, Zhang S, Wang Z, Wang H, Cai S, Yang K, Li A, Jiang Z, Zhang S, Wei X, Huang Y, Sun P, Yang YF, Fisk Z, Si Q, Zhao Z, Sun L. Quantum phase transition and destruction of Kondo effect in pressurized SmB 6. Sci Bull (Beijing) 2017; 62:1439-1444. [PMID: 36659393 DOI: 10.1016/j.scib.2017.10.008] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2017] [Revised: 10/16/2017] [Accepted: 10/16/2017] [Indexed: 01/21/2023]
Abstract
SmB6 has been a well-known Kondo insulator for decades, but recently attracts extensive new attention as a candidate topological system. Studying SmB6 under pressure provides an opportunity to acquire the much-needed understanding about the effect of electron correlations on both the metallic surface state and bulk insulating state. Here we do so by studying the evolution of two transport gaps (low temperature gap El and high temperature gap Eh) associated with the Kondo effect by measuring the electrical resistivity under high pressure and low temperature (0.3 K) conditions. We associate the gaps with the bulk Kondo hybridization, and from their evolution with pressure we demonstrate an insulator-to-metal transition at ∼4 GPa. At the transition pressure, a large change in the Hall number and a divergence tendency of the electron-electron scattering coefficient provide evidence for a destruction of the Kondo entanglement in the ground state. Our results raise the new prospect for studying topological electronic states in quantum critical materials settings.
Collapse
Affiliation(s)
- Yazhou Zhou
- Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Qi Wu
- Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Priscila F S Rosa
- Department of Physics and Astronomy, University of California, Irvine, CA 92697, USA; Los Alamos National Laboratory, Los Alamos, NM 87545, USA
| | - Rong Yu
- Department of Physics, Renmin University of China, Beijing 100872, China; Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China; Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
| | - Jing Guo
- Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Wei Yi
- Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Shan Zhang
- Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Zhe Wang
- Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Honghong Wang
- Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Shu Cai
- Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Ke Yang
- Shanghai Synchrotron Radiation Facilities, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, China
| | - Aiguo Li
- Shanghai Synchrotron Radiation Facilities, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, China
| | - Zheng Jiang
- Shanghai Synchrotron Radiation Facilities, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, China
| | - Shuo Zhang
- Shanghai Synchrotron Radiation Facilities, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, China
| | - Xiangjun Wei
- Shanghai Synchrotron Radiation Facilities, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, China
| | - Yuying Huang
- Shanghai Synchrotron Radiation Facilities, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, China
| | - Peijie Sun
- Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Yi-Feng Yang
- Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China; Collaborative Innovation Center of Quantum Matter, Beijing 100190, China
| | - Zachary Fisk
- Department of Physics and Astronomy, University of California, Irvine, CA 92697, USA
| | - Qimiao Si
- Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China; Department of Physics & Astronomy, Rice University, Houston, TX 77005, USA
| | - Zhongxian Zhao
- Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China; Collaborative Innovation Center of Quantum Matter, Beijing 100190, China; University of Chinese Academy of Sciences, Beijing 100190, China
| | - Liling Sun
- Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China; Collaborative Innovation Center of Quantum Matter, Beijing 100190, China; University of Chinese Academy of Sciences, Beijing 100190, China.
| |
Collapse
|
10
|
Lee JM, Haw SC, Chen SW, Chen SA, Ishii H, Tsuei KD, Hiraoka N, Liao YF, Lu KT, Chen JM. The fluctuating population of Sm 4f configurations in topological Kondo insulator SmB 6 explored with high-resolution X-ray absorption and emission spectra. Dalton Trans 2017; 46:11664-11668. [PMID: 28831472 DOI: 10.1039/c7dt02039b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
High-resolution partial-fluorescence-yield X-ray absorption and resonant X-ray emission spectra were used to characterize the temperature dependence of Sm 4f configurations and orbital/charge degree of freedom in SmB6. The variation of Sm 4f configurations responds well to the formed Kondo gap, below 140 K, and an in-gap state, below 40 K. The topological in-gap state is correlated with the fluctuating population of Sm 4f configurations that arises via carrier transfer between 3d94f6 and 3d94f5 states; both states are partially delocalized, and the mediating 5d orbital plays the role of a transfer path. Complementary results shown in this work thus manifest the importance of configuration fluctuations and orbital delocalization in the topological surface state of SmB6.
Collapse
Affiliation(s)
- Jenn-Min Lee
- National Synchrotron Radiation Research Center (NSRRC), 101 Hsin-Ann Road, 30076 Hsinchu, Taiwan.
| | | | | | | | | | | | | | | | | | | |
Collapse
|
11
|
Ramos E, Franco R, Silva-Valencia J, Foglio ME, Figueira MS. The role of short-range magnetic correlations in the gap opening of topological Kondo insulators. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:345601. [PMID: 28607220 DOI: 10.1088/1361-648x/aa791b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
In this article we investigate the effects of short-range anti-ferromagnetic correlations on the gap opening of topological Kondo insulators. We add a Heisenberg term to the periodic Anderson model at the limit of strong correlations in order to allow a small degree of hopping of the localized electrons between neighboring sites of the lattice. This new model is adequate for studying topological Kondo insulators, whose paradigmatic material is the compound [Formula: see text]. The main finding of the article is that the short-range antiferromagnetic correlations, present in some Kondo insulators, contribute decisively to the opening of the Kondo gap in their density of states. These correlations are produced by the interaction between moments on the neighboring sites of the lattice. For simplicity, we solve the problem on a two dimensional square lattice. The starting point of the model is the [Formula: see text] ions orbitals, with [Formula: see text] multiplet in the presence of spin-orbit coupling. We present results for the Kondo and for the antiferromagnetic correlation functions. We calculate the phase diagram of the model, and as we vary the [Formula: see text] level position from the empty regime to the Kondo regime, the system develops metallic and topological Kondo insulator phases. The band structure calculated shows that the model describes a strong topological insulator.
Collapse
Affiliation(s)
- E Ramos
- Departamento de Física, Universidad Nacional de Colombia, A. A. 5997, Bogotá, Colombia
| | | | | | | | | |
Collapse
|
12
|
Joseph B, Torchio R, Benndorf C, Irifune T, Shinmei T, Pöttgen R, Zerr A. Experimental evidence of an electronic transition in CeP under pressure using Ce L 3 XAS. Phys Chem Chem Phys 2017; 19:17526-17530. [PMID: 28657083 DOI: 10.1039/c7cp03022c] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Cerium phosphide undergoes a unit-cell volume discontinuity without any structural phase transitions upon application of a high pressure of ∼10 GPa. This phenomenon is attributed to a change in the electronic charge distribution of the cerium in CeP, but to date no direct experimental verification for this hypothesis has been presented. Here, we report a Ce L3-edge X-ray absorption spectroscopy study under pressure, which provides direct compelling evidence of an electronic transition associated with the above-mentioned isostructural volume discontinuity. The present results should be relevant to the understanding of the phenomenon of pressure induced isostructural transitions involving unit-cell volume collapse.
Collapse
Affiliation(s)
- B Joseph
- Elettra-Sincrotrone Trieste, Strada Statale 14, Km 163,5, Basovizza, Trieste, Italy.
| | - R Torchio
- European Synchrotron Radiation Facility, BP220, 38043 Grenoble Cedex, France
| | - C Benndorf
- Institut für Anorganische und Analytische Chemie Universitat Münster, Corrensstrasse 30, 48149, Münster, Germany
| | - T Irifune
- Geodynamics Research Center, Ehime University, Bunkyo-cho, 7908577, Matsuyama, Japan
| | - T Shinmei
- Geodynamics Research Center, Ehime University, Bunkyo-cho, 7908577, Matsuyama, Japan
| | - R Pöttgen
- Institut für Anorganische und Analytische Chemie Universitat Münster, Corrensstrasse 30, 48149, Münster, Germany
| | - A Zerr
- Laboratoire des Sciences des Procédés et des Materiaux LSPM-CNRS, Université Paris 13, Sorbonne Paris Cité 93430, Villetaneuse, France
| |
Collapse
|
13
|
Stern A, Dzero M, Galitski VM, Fisk Z, Xia J. Surface-dominated conduction up to 240 K in the Kondo insulator SmB 6 under strain. NATURE MATERIALS 2017; 16:708-711. [PMID: 28369051 DOI: 10.1038/nmat4888] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2016] [Accepted: 03/06/2017] [Indexed: 06/07/2023]
Abstract
SmB6 is a strongly correlated mixed-valence Kondo insulator with a newly discovered surface state, proposed to be of non-trivial topological origin. However, the surface state dominates electrical conduction only below T∗ ≈ 4 K (ref. ), limiting its scientific investigation and device application. Here, we report the enhancement of T∗ in SmB6 under the application of tensile strain. With 0.7% tensile strain we report surface-dominated conduction at up to a temperature of 240 K, persisting even after the strain has been removed. This can be explained in the framework of strain-tuned temporal and spatial fluctuations of f-electron configurations, which might be generally applied to other mixed-valence materials. We note that this amount of strain can be induced in epitaxial SmB6 films via substrate in potential device applications.
Collapse
Affiliation(s)
- A Stern
- Department of Physics and Astronomy, University of California, Irvine, California 92697, USA
| | - M Dzero
- Department of Physics, Kent State University, Kent, Ohio 44242, USA
| | - V M Galitski
- Joint Quantum Institute, Department of Physics, University of Maryland, College Park, Maryland 20742, USA
| | - Z Fisk
- Department of Physics and Astronomy, University of California, Irvine, California 92697, USA
| | - J Xia
- Department of Physics and Astronomy, University of California, Irvine, California 92697, USA
| |
Collapse
|