1
|
Stensberg J, Han X, Lee S, McGill SA, Paglione J, Takeuchi I, Kane CL, Wu L. Observation of the Superconducting Proximity Effect from Surface States in SmB_{6}/YB_{6} Thin Film Heterostructures via Terahertz Spectroscopy. PHYSICAL REVIEW LETTERS 2023; 130:096901. [PMID: 36930917 DOI: 10.1103/physrevlett.130.096901] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2022] [Revised: 08/12/2022] [Accepted: 01/26/2023] [Indexed: 06/18/2023]
Abstract
The ac conduction of epitaxially grown SmB_{6} thin films and superconducting heterostructures of SmB_{6}/YB_{6} are investigated via time-domain terahertz spectroscopy. A two-channel model of thickness-dependent bulk states and thickness-independent surface states accurately describes the measured conductance of bare SmB_{6} thin films, demonstrating the presence of surface states in SmB_{6}. While the observed reductions in the simultaneously measured superconducting gap, transition temperature, and superfluid density of SmB_{6}/YB_{6} heterostructures relative to bare YB_{6} indicate the penetration of proximity-induced superconductivity into the SmB_{6} overlayer; the corresponding SmB_{6}-thickness independence between different heterostructures indicates that the induced superconductivity is predominantly confined to the interface surface state of the SmB_{6}. This study demonstrates the ability of terahertz spectroscopy to probe proximity-induced superconductivity at an interface buried within a heterostructure, and our results show that SmB_{6} behaves as a predominantly insulating bulk surrounded by conducting surface states in both the normal and induced-superconducting states in both terahertz and dc responses, which is consistent with the topological Kondo insulator picture.
Collapse
Affiliation(s)
- Jonathan Stensberg
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Xingyue Han
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Seunghun Lee
- Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA
- Department of Physics, Pukyong National University, Busan 48513, Republic of Korea
| | - Stephen A McGill
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA
| | - Johnpierre Paglione
- Maryland Quantum Materials Center, Department of Physics, University of Maryland, College Park, Maryland 20742, USA
| | - Ichiro Takeuchi
- Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA
- Maryland Quantum Materials Center, Department of Physics, University of Maryland, College Park, Maryland 20742, USA
| | - Charles L Kane
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Liang Wu
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| |
Collapse
|
2
|
Breindel AJ, Deng Y, Moir CM, Fang Y, Ran S, Lou H, Li S, Zeng Q, Shu L, Wolowiec CT, Schuller IK, Rosa PFS, Fisk Z, Singleton J, Maple MB. Probing FeSi, a d-electron topological Kondo insulator candidate, with magnetic field, pressure, and microwaves. Proc Natl Acad Sci U S A 2023; 120:e2216367120. [PMID: 36791111 PMCID: PMC9974408 DOI: 10.1073/pnas.2216367120] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2022] [Accepted: 01/12/2023] [Indexed: 02/16/2023] Open
Abstract
Recently, evidence for a conducting surface state (CSS) below 19 K was reported for the correlated d-electron small gap semiconductor FeSi. In the work reported herein, the CSS and the bulk phase of FeSi were probed via electrical resistivity ρ measurements as a function of temperature T, magnetic field B to 60 T, and pressure P to 7.6 GPa, and by means of a magnetic field-modulated microwave spectroscopy (MFMMS) technique. The properties of FeSi were also compared with those of the Kondo insulator SmB6 to address the question of whether FeSi is a d-electron analogue of an f-electron Kondo insulator and, in addition, a "topological Kondo insulator" (TKI). The overall behavior of the magnetoresistance of FeSi at temperatures above and below the onset temperature TS = 19 K of the CSS is similar to that of SmB6. The two energy gaps, inferred from the ρ(T) data in the semiconducting regime, increase with pressure up to about 7 GPa, followed by a drop which coincides with a sharp suppression of TS. Several studies of ρ(T) under pressure on SmB6 reveal behavior similar to that of FeSi in which the two energy gaps vanish at a critical pressure near the pressure at which TS vanishes, although the energy gaps in SmB6 initially decrease with pressure, whereas in FeSi they increase with pressure. The MFMMS measurements showed a sharp feature at TS ≈ 19 K for FeSi, which could be due to ferromagnetic ordering of the CSS. However, no such feature was observed at TS ≈ 4.5 K for SmB6.
Collapse
Affiliation(s)
| | - Yuhang Deng
- Department of Physics, University of CaliforniaSan Diego, La Jolla, CA92093
| | - Camilla M. Moir
- Department of Physics, University of CaliforniaSan Diego, La Jolla, CA92093
| | - Yuankan Fang
- Department of Physics, University of CaliforniaSan Diego, La Jolla, CA92093
| | - Sheng Ran
- Department of Physics, University of CaliforniaSan Diego, La Jolla, CA92093
| | - Hongbo Lou
- Center for High Pressure Science and Technology Advanced Research, Pudong, Shanghai201203, People’s Republic of China
| | - Shubin Li
- Center for High Pressure Science and Technology Advanced Research, Pudong, Shanghai201203, People’s Republic of China
- Univ Lyon, Université Claude Bernard Lyon 1, CNRS, Institut Lumière Matière, Villeurbanne69100, France
| | - Qiaoshi Zeng
- Center for High Pressure Science and Technology Advanced Research, Pudong, Shanghai201203, People’s Republic of China
| | - Lei Shu
- State Key Laboratory of Surface Physics, Department of Physics, Fudan University, Shanghai200433, People’s Republic of China
- Shanghai Research Center for Quantum Sciences, Shanghai201315, People’s Republic of China
| | | | - Ivan K. Schuller
- Department of Physics, University of CaliforniaSan Diego, La Jolla, CA92093
| | | | - Zachary Fisk
- University of California Irvine, Irvine, CA92967
| | | | - M. Brian Maple
- Department of Physics, University of CaliforniaSan Diego, La Jolla, CA92093
| |
Collapse
|
3
|
Ohtsubo Y, Nakaya T, Nakamura T, Le Fèvre P, Bertran F, Iga F, Kimura SI. Breakdown of bulk-projected isotropy in surface electronic states of topological Kondo insulator SmB 6(001). Nat Commun 2022; 13:5600. [PMID: 36151212 PMCID: PMC9508144 DOI: 10.1038/s41467-022-33347-0] [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: 07/12/2022] [Accepted: 09/12/2022] [Indexed: 11/11/2022] Open
Abstract
The topology and spin-orbital polarization of two-dimensional (2D) surface electronic states have been extensively studied in this decade. One major interest in them is their close relationship with the parities of the bulk (3D) electronic states. In this context, the surface is often regarded as a simple truncation of the bulk crystal. Here we show breakdown of the bulk-related in-plane rotation symmetry in the topological surface states (TSSs) of the Kondo insulator SmB6. Angle-resolved photoelectron spectroscopy (ARPES) performed on the vicinal SmB6(001)-p(2 × 2) surface showed that TSSs are anisotropic and that the Fermi contour lacks the fourfold rotation symmetry maintained in the bulk. This result emphasizes the important role of the surface atomic structure even in TSSs. Moreover, it suggests that the engineering of surface atomic structure could provide a new pathway to tailor various properties among TSSs, such as anisotropic surface conductivity, nesting of surface Fermi contours, or the number and position of van Hove singularities in 2D reciprocal space. Previous work exploring the robustness of topological surface states to perturbations has mostly focused on surfaces with the same atomic structure as the bulk. Here the authors demonstrate the effect of surface reconstruction on the topological surfaces on the (100) surface of SmB6.
Collapse
Affiliation(s)
- Yoshiyuki Ohtsubo
- National Institutes for Quantum Science and Technology, Sendai, 980-8579, Japan. .,Graduate School of Frontier Biosciences, Osaka University, Suita, 565-0871, Japan. .,Department of Physics, Graduate School of Science, Osaka University, Toyonaka, 560-0043, Japan.
| | - Toru Nakaya
- Department of Physics, Graduate School of Science, Osaka University, Toyonaka, 560-0043, Japan
| | - Takuto Nakamura
- Graduate School of Frontier Biosciences, Osaka University, Suita, 565-0871, Japan.,Department of Physics, Graduate School of Science, Osaka University, Toyonaka, 560-0043, Japan
| | - Patrick Le Fèvre
- Synchrotron SOLEIL, L'Orme des Merisiers, Départementale 128, F-91190, Saint-Aubin, France
| | - François Bertran
- Synchrotron SOLEIL, L'Orme des Merisiers, Départementale 128, F-91190, Saint-Aubin, France
| | - Fumitoshi Iga
- Graduate School of Science and Engineering, Ibaraki University, Mito, 310-8512, Japan
| | - Shin-Ichi Kimura
- Graduate School of Frontier Biosciences, Osaka University, Suita, 565-0871, Japan. .,Department of Physics, Graduate School of Science, Osaka University, Toyonaka, 560-0043, Japan. .,Institute for Molecular Science, Okazaki, 444-8585, Japan.
| |
Collapse
|
4
|
Aishwarya A, Cai Z, Raghavan A, Romanelli M, Wang X, Li X, Gu GD, Hirsbrunner M, Hughes T, Liu F, Jiao L, Madhavan V. Spin-selective tunneling from nanowires of the candidate topological Kondo insulator SmB 6. Science 2022; 377:1218-1222. [PMID: 36074835 DOI: 10.1126/science.abj8765] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Incorporating relativistic physics into quantum tunneling can lead to exotic behavior such as perfect transmission through Klein tunneling. Here, we probed the tunneling properties of spin-momentum-locked relativistic fermions by designing and implementing a tunneling geometry that uses nanowires of the topological Kondo insulator candidate samarium hexaboride. The nanowires are attached to the end of scanning tunneling microscope tips and used to image the bicollinear stripe spin order in the antiferromagnet Fe1.03Te with a Neel temperature of about 50 kelvin. The antiferromagnetic stripes become invisible above 10 kelvin concomitant with the suppression of the topological surface states in the tip. We further demonstrate that the direction of spin polarization is tied to the tunneling direction. Our technique establishes samarium hexaboride nanowires as ideal conduits for spin-polarized currents.
Collapse
Affiliation(s)
- Anuva Aishwarya
- Department of Physics and Materials Research Laboratory, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA
| | - Zhuozhen Cai
- Department of Physics and Materials Research Laboratory, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA
| | - Arjun Raghavan
- Department of Physics and Materials Research Laboratory, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA
| | - Marisa Romanelli
- Department of Physics and Materials Research Laboratory, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA
| | - Xiaoyu Wang
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA
| | - Xu Li
- State Key Laboratory of Optoelectronic Materials and Technologies, Guangdong Province Key Laboratory of Display Material and Technology, and School of Electronics and Information Technology, Sun Yat-sen University, Guangzhou 510275, China
| | - G D Gu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA
| | - Mark Hirsbrunner
- Department of Physics and Materials Research Laboratory, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA
| | - Taylor Hughes
- Department of Physics and Materials Research Laboratory, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA
| | - Fei Liu
- State Key Laboratory of Optoelectronic Materials and Technologies, Guangdong Province Key Laboratory of Display Material and Technology, and School of Electronics and Information Technology, Sun Yat-sen University, Guangzhou 510275, China
| | - Lin Jiao
- Department of Physics and Materials Research Laboratory, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA.,National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA
| | - Vidya Madhavan
- Department of Physics and Materials Research Laboratory, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA
| |
Collapse
|
5
|
Cui Y, Chu Y, Pan Z, Xing Y, Huang S, Xu H. Anisotropic magnetoresistance as evidence of spin-momentum inter-locking in topological Kondo insulator SmB 6 nanowires. NANOSCALE 2021; 13:20417-20424. [PMID: 34878477 DOI: 10.1039/d1nr07047a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
SmB6, which opens up an insulating bulk gap due to hybridization between itinerant d-electrons and localized f-electrons below a critical temperature, turns out to be a topological Kondo insulator possessing exotic conducting states on its surface. However, measurement of the surface-states in SmB6 draws controversial conclusions, depending on the growth methods and experimental techniques used. Herein, we report anisotropic magnetoresistance (AMR) observed in the Kondo energy gap of a single SmB6 nanowire that is immune to magnetic dopant pollution and features a square cross-section to show high-symmetry crystal facets. The AMR clearly shows a cosine function of included angle θ between magnetic field and measuring current with a period of π. The positive AMR is interpreted by anisotropically lifting the topological protection of spin-momentum inter-locking surface-states by rotating the in-plane magnetic field, which, therefore, provides the transport evidence that supports the topologically nontrivial nature of the SmB6 surface-states.
Collapse
Affiliation(s)
- Yugui Cui
- Beijing Key Laboratory of Quantum Devices, Key Laboratory for the Physics and Chemistry of Nanodevices, and Department of Electronics, Peking University, Beijing, 100871, P. R. China.
| | - Yi Chu
- Beijing Key Laboratory of Quantum Devices, Key Laboratory for the Physics and Chemistry of Nanodevices, and Department of Electronics, Peking University, Beijing, 100871, P. R. China.
| | - Zhencun Pan
- Beijing Key Laboratory of Quantum Devices, Key Laboratory for the Physics and Chemistry of Nanodevices, and Department of Electronics, Peking University, Beijing, 100871, P. R. China.
| | - Yingjie Xing
- Beijing Key Laboratory of Quantum Devices, Key Laboratory for the Physics and Chemistry of Nanodevices, and Department of Electronics, Peking University, Beijing, 100871, P. R. China.
| | - Shaoyun Huang
- Beijing Key Laboratory of Quantum Devices, Key Laboratory for the Physics and Chemistry of Nanodevices, and Department of Electronics, Peking University, Beijing, 100871, P. R. China.
| | - Hongqi Xu
- Beijing Key Laboratory of Quantum Devices, Key Laboratory for the Physics and Chemistry of Nanodevices, and Department of Electronics, Peking University, Beijing, 100871, P. R. China.
| |
Collapse
|
6
|
Liu JY, Yu J, Ning JL, Yi HM, Miao L, Min LJ, Zhao YF, Ning W, Lopez KA, Zhu YL, Pillsbury T, Zhang YB, Wang Y, Hu J, Cao HB, Chakoumakos BC, Balakirev F, Weickert F, Jaime M, Lai Y, Yang K, Sun JW, Alem N, Gopalan V, Chang CZ, Samarth N, Liu CX, McDonald RD, Mao ZQ. Spin-valley locking and bulk quantum Hall effect in a noncentrosymmetric Dirac semimetal BaMnSb 2. Nat Commun 2021; 12:4062. [PMID: 34210963 PMCID: PMC8249485 DOI: 10.1038/s41467-021-24369-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2020] [Accepted: 06/16/2021] [Indexed: 02/06/2023] Open
Abstract
Spin-valley locking in monolayer transition metal dichalcogenides has attracted enormous interest, since it offers potential for valleytronic and optoelectronic applications. Such an exotic electronic state has sparsely been seen in bulk materials. Here, we report spin-valley locking in a Dirac semimetal BaMnSb2. This is revealed by comprehensive studies using first principles calculations, tight-binding and effective model analyses, angle-resolved photoemission spectroscopy measurements. Moreover, this material also exhibits a stacked quantum Hall effect (QHE). The spin-valley degeneracy extracted from the QHE is close to 2. This result, together with the Landau level spin splitting, further confirms the spin-valley locking picture. In the extreme quantum limit, we also observed a plateau in the z-axis resistance, suggestive of a two-dimensional chiral surface state present in the quantum Hall state. These findings establish BaMnSb2 as a rare platform for exploring coupled spin and valley physics in bulk single crystals and accessing 3D interacting topological states.
Collapse
Affiliation(s)
- J Y Liu
- Department of Physics and Engineering Physics, Tulane University, New Orleans, LA, USA
- Department of Physics and Astronomy, University of California, Irvine, CA, USA
| | - J Yu
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
- Condensed Matter Theory Center, Department of Physics, University of Maryland, College Park, MD, USA
| | - J L Ning
- Department of Physics and Engineering Physics, Tulane University, New Orleans, LA, USA
| | - H M Yi
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - L Miao
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, USA
| | - L J Min
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, USA
| | - Y F Zhao
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - W Ning
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - K A Lopez
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, USA
| | - Y L Zhu
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - T Pillsbury
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Y B Zhang
- Department of Physics and Engineering Physics, Tulane University, New Orleans, LA, USA
| | - Y Wang
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - J Hu
- Department of Physics, University of Arkansas, Fayetteville, AR, USA
| | - H B Cao
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA
| | - B C Chakoumakos
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA
| | - F Balakirev
- Los Alamos National Laboratory, Los Alamos, NM, USA
| | - F Weickert
- Los Alamos National Laboratory, Los Alamos, NM, USA
| | - M Jaime
- Los Alamos National Laboratory, Los Alamos, NM, USA
| | - Y Lai
- Los Alamos National Laboratory, Los Alamos, NM, USA
| | - Kun Yang
- Physics Department and National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, USA
| | - J W Sun
- Department of Physics and Engineering Physics, Tulane University, New Orleans, LA, USA
| | - N Alem
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, USA
| | - V Gopalan
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, USA
| | - C Z Chang
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - N Samarth
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - C X Liu
- Department of Physics, The Pennsylvania State University, University Park, PA, USA.
| | - R D McDonald
- Los Alamos National Laboratory, Los Alamos, NM, USA.
| | - Z Q Mao
- Department of Physics and Engineering Physics, Tulane University, New Orleans, LA, USA.
- Department of Physics, The Pennsylvania State University, University Park, PA, USA.
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, USA.
| |
Collapse
|
7
|
Atomistic investigation of surface characteristics and electronic features at high-purity FeSi(110) presenting interfacial metallicity. Proc Natl Acad Sci U S A 2021; 118:2021203118. [PMID: 33879612 DOI: 10.1073/pnas.2021203118] [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
Iron silicide (FeSi) is a fascinating material that has attracted extensive research efforts for decades, notably revealing unusual temperature-dependent electronic and magnetic characteristics, as well as a close resemblance to the Kondo insulators whereby a coherent picture of intrinsic properties and underlying physics remains to be fully developed. For a better understanding of this narrow-gap semiconductor, we prepared and examined FeSi(110) single-crystal surfaces of high quality. Combined insights from low-temperature scanning tunneling microscopy and density functional theory calculations (DFT) indicate an unreconstructed surface termination presenting rows of Fe-Si pairs. Using high-resolution tunneling spectroscopy (STS), we identify a distinct asymmetric electronic gap in the sub-10 K regime on defect-free terraces. Moreover, the STS data reveal a residual density of states in the gap regime whereby two in-gap states are recognized. The principal origin of these features is rationalized with the help of the DFT-calculated band structure. The computational modeling of a (110)-oriented slab notably evidences the existence of interfacial intragap bands accounting for a markedly increased density of states around the Fermi level. These findings support and provide further insight into the emergence of surface metallicity in the low-temperature regime.
Collapse
|
8
|
Miao L, Min CH, Xu Y, Huang Z, Kotta EC, Basak R, Song MS, Kang BY, Cho BK, Kißner K, Reinert F, Yilmaz T, Vescovo E, Chuang YD, Wu W, Denlinger JD, Wray LA. Robust Surface States and Coherence Phenomena in Magnetically Alloyed SmB_{6}. PHYSICAL REVIEW LETTERS 2021; 126:136401. [PMID: 33861118 DOI: 10.1103/physrevlett.126.136401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2020] [Revised: 01/19/2021] [Accepted: 03/05/2021] [Indexed: 06/12/2023]
Abstract
Samarium hexaboride is a candidate for the topological Kondo insulator state, in which Kondo coherence is predicted to give rise to an insulating gap spanned by topological surface states. Here we investigate the surface and bulk electronic properties of magnetically alloyed Sm_{1-x}M_{x}B_{6} (M=Ce, Eu), using angle-resolved photoemission spectroscopy and complementary characterization techniques. Remarkably, topologically nontrivial bulk and surface band structures are found to persist in highly modified samples with up to 30% Sm substitution and with an antiferromagnetic ground state in the case of Eu doping. The results are interpreted in terms of a hierarchy of energy scales, in which surface state emergence is linked to the formation of a direct Kondo gap, while low-temperature transport trends depend on the indirect gap.
Collapse
Affiliation(s)
- Lin Miao
- School of Physics, Southeast University, Nanjing 211189, China
| | - Chul-Hee Min
- Experimentelle Physik VII and Würzburg-Dresden Cluster of Excellence ct.qmat, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - Yishuai Xu
- Department of Physics, New York University, New York, New York 10003, USA
| | - Zengle Huang
- Rutgers Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA
| | - Erica C Kotta
- Department of Physics, New York University, New York, New York 10003, USA
| | - Rourav Basak
- Department of Physics, New York University, New York, New York 10003, USA
| | - M S Song
- School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, Korea
| | - B Y Kang
- School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, Korea
| | - B K Cho
- School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, Korea
| | - K Kißner
- Experimentelle Physik VII and Würzburg-Dresden Cluster of Excellence ct.qmat, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - F Reinert
- Experimentelle Physik VII and Würzburg-Dresden Cluster of Excellence ct.qmat, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - Turgut Yilmaz
- National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Elio Vescovo
- National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Yi-De Chuang
- Rutgers Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA
| | - Weida Wu
- Rutgers Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA
| | - Jonathan D Denlinger
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - L Andrew Wray
- Department of Physics, New York University, New York, New York 10003, USA
| |
Collapse
|
9
|
Ryu DC, Kim J, Choi H, Min BI. Wallpaper Dirac Fermion in a Nonsymmorphic Topological Kondo Insulator: PuB 4. J Am Chem Soc 2020; 142:19278-19282. [PMID: 33113332 DOI: 10.1021/jacs.0c09442] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
It has been recently predicted that nonsymmorphic crystalline insulators can host two exotic topological surface states (TSSs). One is the "hourglass fermion", and the other is the "wallpaper Dirac fermion". For the former, a few real materials were predicted and already confirmed experimentally. For the latter, however, no bulk-insulating and experimentally accessible candidate has been identified yet. Here we show that the localized 5f-electrons in PuB4, the single crystal of which was recently synthesized and was found to exhibit Kondo-insulating nature, form a closed manifold over the Brillouin zone via the Kondo coherence effect at low temperature, and host hitherto unobserved wallpaper Dirac fermions at the nonsymmorphic symmetry-preserving (001) surface. The topological nature of TSSs in PuB4 can be described by topological invariants of two Z4 indices [(χx, χy) = (1, 1)] of double-glide symmetries of p4g wallpaper group; thus, PuB4 is a 3D nonsymmorphic topological insulator that exhibits the TSSs of peculiar 4-fold surface Dirac fermions as well as 2-fold double-glide spin-Hall and nodal-line-type fermions. On top of its interesting 5f-electron Kondo-insulating nature, the unique 4-fold wallpaper Dirac fermions in PuB4, which are quite distinct from previously reported nonsymmorphic Dirac insulator or hourglass TCI fermions, broaden our recognition of the embedded fermions in strongly correlated Kondo systems with nonsymmorphic symmetries.
Collapse
Affiliation(s)
- Dong-Choon Ryu
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
| | - Junwon Kim
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
| | - Hongchul Choi
- IBS Center for Correlated Electron Systems, Seoul National University, Seoul 08826, Korea
| | - Byung Il Min
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
| |
Collapse
|
10
|
Crystal Growth by the Floating Zone Method of Ce-Substituted Crystals of the Topological Kondo Insulator SmB6. CRYSTALS 2020. [DOI: 10.3390/cryst10090827] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
SmB6 is a mixed valence topological Kondo insulator. To investigate the effect of substituting Sm with magnetic Ce ions on the physical properties of samarium hexaboride, Ce-substituted SmB6 crystals were grown by the floating zone method for the first time as large, good quality single crystal boules. The crystal growth conditions are reported. Structural, magnetic and transport properties of single crystals of Sm1−xCexB6 (x=0.05, 0.10 and 0.20) were investigated using X-ray diffraction techniques, electrical resistivity and magnetisation measurements. Phase composition analysis of the powder X-ray diffraction data collected on the as-grown boules revealed that the main phase was that of the parent compound, SmB6. Substitution of Sm ions with magnetic Ce ions does not lead to long-range magnetic ordering in the Sm1−xCexB6 crystals. The substitution with 5% Ce and above suppresses the cross-over from bulk conductivity at high temperatures to surface-only conductivity at low temperatures.
Collapse
|
11
|
Heath JT, Bedell KS. Universal signatures of Majorana-like quasiparticles in strongly correlated Landau-Fermi liquids. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:485602. [PMID: 32903219 DOI: 10.1088/1361-648x/abaeb0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2019] [Accepted: 08/12/2020] [Indexed: 06/11/2023]
Abstract
Motivated by recent experiments in the Kitaev honeycomb lattice, Kondo insulators, and the 'Luttinger's theorem-violating' Fermi liquid phase of the underdoped cuprates, we extend the theoretical machinery of Landau-Fermi liquid theory to a system of itinerant, interacting Majorana-like particles. Building upon a previously introduced model of 'nearly self-conjugate' fermionic polarons, a Landau-Majorana kinetic equation is introduced to describe the collective modes and Fermi surface instabilities in a fluid of particles whose fermionic degrees of freedom obey the Majorana reality condition. At large screening, we show that the Landau-Majorana liquid harbors a Lifshitz transition for specific values of the driving frequency. Moreover, we find the dispersion of the zero sound collective mode in such a system, showing that there exists a specific limit where the Landau-Majorana liquid harbors a stability against Pomeranchuk deformations unseen in the conventional Landau-Fermi liquid. With these results, our work paves the way for possible extensions of the Landau quasiparticle paradigm to nontrivial metallic phases of matter.
Collapse
Affiliation(s)
- Joshuah T Heath
- Physics Department, Boston College, Chestnut Hill, Massachusetts 02467, United States of America
| | - Kevin S Bedell
- Physics Department, Boston College, Chestnut Hill, Massachusetts 02467, United States of America
| |
Collapse
|
12
|
Metallic surface states in a correlated d-electron topological Kondo insulator candidate FeSb 2. Proc Natl Acad Sci U S A 2020; 117:15409-15413. [PMID: 32571928 DOI: 10.1073/pnas.2002361117] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The resistance of a conventional insulator diverges as temperature approaches zero. The peculiar low-temperature resistivity saturation in the 4f Kondo insulator (KI) SmB6 has spurred proposals of a correlation-driven topological Kondo insulator (TKI) with exotic ground states. However, the scarcity of model TKI material families leaves difficulties in disentangling key ingredients from irrelevant details. Here we use angle-resolved photoemission spectroscopy (ARPES) to study FeSb2, a correlated d-electron KI candidate that also exhibits a low-temperature resistivity saturation. On the (010) surface, we find a rich assemblage of metallic states with two-dimensional dispersion. Measurements of the bulk band structure reveal band renormalization, a large temperature-dependent band shift, and flat spectral features along certain high-symmetry directions, providing spectroscopic evidence for strong correlations. Our observations suggest that exotic insulating states resembling those in SmB6 and YbB12 may also exist in systems with d instead of f electrons.
Collapse
|
13
|
Khan SU, Khan WU, Khan WU, Khan D, Saeed S, Badshah S, Ikram M, Saleh TA. Eu 3+ , Sm 3+ Deep-Red Phosphors as Novel Materials for White Light-Emitting Diodes and Simultaneous Performance Enhancement of Organic-Inorganic Perovskite Solar Cells. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2020; 16:e2001551. [PMID: 32459055 DOI: 10.1002/smll.202001551] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Revised: 04/15/2020] [Accepted: 04/21/2020] [Indexed: 06/11/2023]
Abstract
The luminous efficiency of inorganic white light-emitting diodes, to be used by the next generation as light initiators, is continuously progressing and is an emerging interest for researchers. However, low color-rendering index (Ra), high correlated color temperature (CCT), and poor stability limit its wider application. Herein, it is reported that Sm3+ - and Eu3+ -doped calcium scandate (CaSc2 O4 (CSO)) are an emerging deep-red-emitting material with promising light absorption, enhanced emission properties, and excellent thermal stability that make it a promising candidate with potential applications in emission display, solid-state white lighting, and the device performance of perovskite solar cells (PSCs). The average crystal structures of Sm3+ -doped CSO are studied by synchrotron X-ray data that correspond to an extremely rigid host structure. Samarium ion is incorporated as a sensitizer that enhances the emission intensity up to 30%, with a high color purity of 88.9% with a 6% increment. The impacts of hosting the sensitizer are studied by quantifying the lifetime curves. The CaSc2 O4 :0.15Eu3+ ,0.03Sm3+ phosphor offers significant resistance to thermal quenching. The incorporation of lanthanide ion-doped phosphors CSOE into PSCs is investigated along with their potential applications. The CSOE-coated PSCs devices exhibit a high current density and a high power conversion efficiency (15.96%) when compared to the uncoated control devices.
Collapse
Affiliation(s)
- Shahid Ullah Khan
- College of Plant Sciences and Technology, Huazhong Agricultural University, Wuhan, 430070, P. R. China
- Institute of Chemical Sciences, Gomal University, Dera Ismail Khan, Khyber Pakhtunkhwa, 29050, Pakistan
| | - Waheed Ullah Khan
- School of Physical Science and Technology, Lanzhou University, Lanzhou, 730000, P. R. China
| | - Wasim Ullah Khan
- State Key Laboratory of Optoelectronic Materials and Technologies, School of Materials Science and Engineering, Sun Yat-sen University, Guangzhou, 510275, P. R. China
| | - Dilfaraz Khan
- Institute of Chemical Sciences, Gomal University, Dera Ismail Khan, Khyber Pakhtunkhwa, 29050, Pakistan
| | - Sumbul Saeed
- College of Plant Sciences and Technology, Huazhong Agricultural University, Wuhan, 430070, P. R. China
| | - Syed Badshah
- Institute of Chemical Sciences, Gomal University, Dera Ismail Khan, Khyber Pakhtunkhwa, 29050, Pakistan
| | - Muhammad Ikram
- Statistical Genomics Laboratory, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, 430070, P. R. China
| | - Tawfik A Saleh
- Department of Chemistry, King Fahd University of Petroleum & Minerals, Dhahran, 31261, Saudi Arabia
| |
Collapse
|
14
|
Herrmann H, Hlawenka P, Siemensmeyer K, Weschke E, Sánchez-Barriga J, Varykhalov A, Shitsevalova NY, Dukhnenko AV, Filipov VB, Gabáni S, Flachbart K, Rader O, Sterrer M, Rienks EDL. Contrast Reversal in Scanning Tunneling Microscopy and Its Implications for the Topological Classification of SmB 6. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2020; 32:e1906725. [PMID: 31997471 DOI: 10.1002/adma.201906725] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/14/2019] [Revised: 12/06/2019] [Indexed: 06/10/2023]
Abstract
SmB6 has recently attracted considerable interest as a candidate for the first strongly correlated topological insulator. Such materials promise entirely new properties such as correlation-enhanced bulk bandgaps or a Fermi surface from spin excitations. Whether SmB6 and its surface states are topological or trivial is still heavily disputed however, and a solution is hindered by major disagreement between angle-resolved photoemission (ARPES) and scanning tunneling microscopy (STM) results. Here, a combined ARPES and STM experiment is conducted. It is discovered that the STM contrast strongly depends on the bias voltage and reverses its sign beyond 1 V. It is shown that the understanding of this contrast reversal is the clue to resolving the discrepancy between ARPES and STM results. In particular, the scanning tunneling spectra reflect a low-energy electronic structure at the surface, which supports a trivial origin of the surface states and the surface metallicity of SmB6 .
Collapse
Affiliation(s)
- Hannes Herrmann
- Institut für Physik, Karl-Franzens-Universität Graz, Universitätsplatz 5, 8010, Graz, Austria
| | - Peter Hlawenka
- Helmholtz-Zentrum Berlin für Materialien und Energie, Elektronenspeicherring BESSY II, Albert-Einstein-Straße 15, 12489, Berlin, Germany
| | - Konrad Siemensmeyer
- Helmholtz-Zentrum Berlin für Materialien und Energie, Elektronenspeicherring BESSY II, Albert-Einstein-Straße 15, 12489, Berlin, Germany
| | - Eugen Weschke
- Helmholtz-Zentrum Berlin für Materialien und Energie, Elektronenspeicherring BESSY II, Albert-Einstein-Straße 15, 12489, Berlin, Germany
| | - Jaime Sánchez-Barriga
- Helmholtz-Zentrum Berlin für Materialien und Energie, Elektronenspeicherring BESSY II, Albert-Einstein-Straße 15, 12489, Berlin, Germany
| | - Andrei Varykhalov
- Helmholtz-Zentrum Berlin für Materialien und Energie, Elektronenspeicherring BESSY II, Albert-Einstein-Straße 15, 12489, Berlin, Germany
| | - Natalya Y Shitsevalova
- Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, Krzhyzhanovsky str. 3, 03142, Kiev, Ukraine
| | - Anatoliy V Dukhnenko
- Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, Krzhyzhanovsky str. 3, 03142, Kiev, Ukraine
| | - Volodymyr B Filipov
- Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, Krzhyzhanovsky str. 3, 03142, Kiev, Ukraine
| | - Slavomir Gabáni
- Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 04001, Košice, Slovakia
| | - Karol Flachbart
- Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 04001, Košice, Slovakia
| | - Oliver Rader
- Helmholtz-Zentrum Berlin für Materialien und Energie, Elektronenspeicherring BESSY II, Albert-Einstein-Straße 15, 12489, Berlin, Germany
| | - Martin Sterrer
- Institut für Physik, Karl-Franzens-Universität Graz, Universitätsplatz 5, 8010, Graz, Austria
| | - Emile D L Rienks
- Helmholtz-Zentrum Berlin für Materialien und Energie, Elektronenspeicherring BESSY II, Albert-Einstein-Straße 15, 12489, Berlin, Germany
- Institut für Festkörperphysik, Technische Universität Dresden, 01062, Dresden, Germany
- Leibniz-Institut für Festkörper- und Werkstoffforschung Dresden, Helmholtzstraße 20, 01069, Dresden, Germany
| |
Collapse
|
15
|
Abstract
SmB6 has drawn much attention in recent times due to the discovery of anomalies in its ground state properties as well as prediction of topologically protected gapless surface states. Varied theories have been proposed to capture the ground state anomalies. Here, we studied the electronic structure of SmB6 employing density functional theory using different exchange correlation potentials, spin-orbit coupling and electron correlation strength. We discover that a suitable choice of interaction parameters such as spin-orbit coupling, electron correlation strength and exchange interaction within the generalized gradient approximation provides a good description of the spectral functions observed in the angle-resolved photoemission spectroscopy (ARPES) studies. The Fermi surface plots exhibit electron pockets around X-point and hole pockets around ΓX line having dominant Sm 4f character. These observations corroborate well with the recent experimental results involving quantum oscillation measurements, ARPES, etc. In addition to primarily Sm 4f contributions observed at the Fermi level, the results exhibit significantly large contribution from B 2p states compared to weak Sm 5d contributions. This suggests important role of B 2p - Sm 4f hybridization in the exotic physics of this system.
Collapse
Affiliation(s)
- Anup Pradhan Sakhya
- Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai, 400 005, India
| | - Kalobaran Maiti
- Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai, 400 005, India.
| |
Collapse
|
16
|
Gheidi S, Akintola K, Akella KS, Côté AM, Dunsiger SR, Broholm C, Fuhrman WT, Saha SR, Paglione J, Sonier JE. Intrinsic Low-Temperature Magnetism in SmB_{6}. PHYSICAL REVIEW LETTERS 2019; 123:197203. [PMID: 31765191 DOI: 10.1103/physrevlett.123.197203] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Revised: 07/29/2019] [Indexed: 06/10/2023]
Abstract
By means of new muon spin relaxation experiments, we disentangle extrinsic and intrinsic sources of low-temperature bulk magnetism in the candidate topological Kondo insulator (TKI) SmB_{6}. Results on Al-flux-grown SmB_{6} single crystals are compared to those on a large floating-zone-grown ^{154}Sm ^{11}B_{6} single crystal in which a 14 meV bulk spin exciton has been detected by inelastic neutron scattering. Below ∼10 K, we detect the gradual development of quasistatic magnetism due to rare-earth impurities and Sm vacancies. Our measurements also reveal two additional forms of intrinsic magnetism: (1) underlying low-energy (∼100 meV) weak magnetic moment (∼10^{-2} μ_{B}) fluctuations similar to those detected in the related candidate TKI YbB_{12} that persist down to millikelvin temperatures, and (2) magnetic fluctuations consistent with a 2.6 meV bulk magnetic excitation at zero magnetic field that appears to hinder surface conductivity above ∼4.5 K. We discuss potential origins of the magnetism.
Collapse
Affiliation(s)
- S Gheidi
- Department of Physics, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
| | - K Akintola
- Department of Physics, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
| | - K S Akella
- Department of Physics, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
| | - A M Côté
- Department of Physics, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
- Kwantlen Polytechnic University, Richmond, British Columbia V6X 3X7, Canada
| | - S R Dunsiger
- Department of Physics, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
- Centre for Molecular and Materials Science, TRIUMF, Vancouver, British Columbia V6T 2A3, Canada
| | - C Broholm
- Institute for Quantum Matter and Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218, USA
- Department of Materials Science and Engineering, The Johns Hopkins University, Baltimore, Maryland 21218, USA
- Canadian Institute for Advanced Research, Toronto, Ontario M5G 1Z8, Canada
| | - W T Fuhrman
- Center for Nanophysics and Advanced Materials, Department of Physics, University of Maryland, College Park, Maryland 20742, USA
| | - S R Saha
- Center for Nanophysics and Advanced Materials, Department of Physics, University of Maryland, College Park, Maryland 20742, USA
| | - J Paglione
- Canadian Institute for Advanced Research, Toronto, Ontario M5G 1Z8, Canada
- Center for Nanophysics and Advanced Materials, Department of Physics, University of Maryland, College Park, Maryland 20742, USA
| | - J E Sonier
- Department of Physics, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
- Canadian Institute for Advanced Research, Toronto, Ontario M5G 1Z8, Canada
| |
Collapse
|
17
|
Radwanski RJ, Nalecz DM, Ropka Z. Breakdown of the strong multiplet description of the Sm 2+ ion in the topological Kondo insulator SmB 6: specific heat studies. Sci Rep 2019; 9:11330. [PMID: 31383917 PMCID: PMC6683202 DOI: 10.1038/s41598-019-47776-3] [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: 02/25/2019] [Accepted: 07/24/2019] [Indexed: 11/25/2022] Open
Abstract
We have theoretically confirmed the existence of in-gap real quantum-mechanical states in SmB6, which have been suggested by experiments. These in-gap states, below the hybridization gap of 20 meV, are related to the Sm2+ ion states and can be revealed by calculations within the spin-orbital |LSLzSz〉 space, with L = 3 and S = 3. Our approach overcomes difficulties related to the singlet J = 0 multiplet ground state. The in-gap states originate from the 49-fold degenerated term 7F (4f 6), which is split by cubic crystal-field (CEF) and spin-orbit (s − o) interactions. There is competition between these interactions: the six-order CEF interactions produce a 7-fold degenerated ground state, whereas the s − o interactions, even the weakest one, produce a singlet (J = 0) ground state. We have found preliminary CEF and s − o parameters that produce the lowest states at 0 K (singlet) and 91 K (triplet) and the next triplet at 221 K, i.e., within the hybridization gap. The derived states well explain the large extra specific heat of SmB6, confirming the consistency and adequateness of our theoretical approach with the breakdown of the strong multiplet description of the Sm2+ ion in SmB6.
Collapse
Affiliation(s)
- Ryszard J Radwanski
- Institute of Physics, Pedagogical University, Krakow, 30-084, Poland. .,Center of Solid State Physics, Krakow, 31-150, Poland.
| | - Dawid M Nalecz
- Institute of Physics, Pedagogical University, Krakow, 30-084, Poland
| | - Zofia Ropka
- Center of Solid State Physics, Krakow, 31-150, Poland
| |
Collapse
|
18
|
Non-trivial surface states of samarium hexaboride at the (111) surface. Nat Commun 2019; 10:2298. [PMID: 31127112 PMCID: PMC6534584 DOI: 10.1038/s41467-019-10353-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2018] [Accepted: 05/08/2019] [Indexed: 11/24/2022] Open
Abstract
The peculiar metallic electronic states observed in the Kondo insulator, samarium hexaboride (SmB6), has stimulated considerable attention among those studying non-trivial electronic phenomena. However, experimental studies of these states have led to controversial conclusions mainly due to the difficulty and inhomogeneity of the SmB6 crystal surface. Here, we show the detailed electronic structure of SmB6 with angle-resolved photoelectron spectroscopy measurements of the three-fold (111) surface where only two inequivalent time-reversal-invariant momenta (TRIM) exist. We observe the metallic two-dimensional state was dispersed across the bulk Kondo gap. Its helical in-plane spin polarisation around the surface TRIM indicates that SmB6 is topologically non-trivial, according to the topological classification theory for weakly correlated systems. Based on these results, we propose a simple picture of the controversial topological classification of SmB6. Samarium hexaboride has unusual electronic properties that have been suggested to arise from topological effects. Here the authors present spin-resolved ARPES measurements of the (111) surface and observe surface states that may give insight into the bulk topological properties.
Collapse
|
19
|
Thomas SM, Ding X, Ronning F, Zapf V, Thompson JD, Fisk Z, Xia J, Rosa PFS. Quantum Oscillations in Flux-Grown SmB_{6} with Embedded Aluminum. PHYSICAL REVIEW LETTERS 2019; 122:166401. [PMID: 31075018 DOI: 10.1103/physrevlett.122.166401] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2018] [Revised: 09/14/2018] [Indexed: 06/09/2023]
Abstract
SmB_{6} is a candidate topological Kondo insulator that displays surface conduction at low temperatures. Here, we perform torque magnetization measurements as a means to detect de Haas-van Alphen (dHvA) oscillations in SmB_{6} crystals grown by aluminum flux. We find that dHvA oscillations occur in single crystals containing embedded aluminum, originating from the flux used to synthesize SmB_{6}. Measurements on a sample with multiple, unconnected aluminum inclusions show that aluminum crystallizes in a preferred orientation within the SmB_{6} cubic lattice. The presence of aluminum is confirmed through bulk susceptibility measurements, but does not show a signature in transport measurements. We discuss the ramifications of our results.
Collapse
Affiliation(s)
- S M Thomas
- Department of Physics and Astronomy, University of California, Irvine, California 92967, USA
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - Xiaxin Ding
- National High Magnetic Field Laboratory, Los Alamos, New Mexico 87545, USA
| | - F Ronning
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - V Zapf
- National High Magnetic Field Laboratory, Los Alamos, New Mexico 87545, USA
| | - J D Thompson
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - Z Fisk
- Department of Physics and Astronomy, University of California, Irvine, California 92967, USA
| | - J Xia
- Department of Physics and Astronomy, University of California, Irvine, California 92967, USA
| | - P F S Rosa
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| |
Collapse
|
20
|
Jiao L, Rößler S, Kasinathan D, Rosa PFS, Guo C, Yuan H, Liu CX, Fisk Z, Steglich F, Wirth S. Magnetic and defect probes of the SmB 6 surface state. SCIENCE ADVANCES 2018; 4:eaau4886. [PMID: 30430137 PMCID: PMC6226282 DOI: 10.1126/sciadv.aau4886] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/15/2018] [Accepted: 10/12/2018] [Indexed: 06/09/2023]
Abstract
The impact of nonmagnetic and magnetic impurities on topological insulators is a central focus concerning their fundamental physics and possible spintronics and quantum computing applications. Combining scanning tunneling spectroscopy with transport measurements, we investigate, both locally and globally, the effect of nonmagnetic and magnetic substituents in SmB6, a predicted topological Kondo insulator. Around the so-introduced substitutents and in accord with theoretical predictions, the surface states are locally suppressed with different length scales depending on the substituent's magnetic properties. For sufficiently high substituent concentrations, these states are globally destroyed. Similarly, using a magnetic tip in tunneling spectroscopy also resulted in largely suppressed surface states. Hence, a destruction of the surface states is always observed close to atoms with substantial magnetic moment. This points to the topological nature of the surface states in SmB6 and illustrates how magnetic impurities destroy the surface states from microscopic to macroscopic length scales.
Collapse
Affiliation(s)
- Lin Jiao
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany
| | - Sahana Rößler
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany
| | - Deepa Kasinathan
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany
| | - 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
| | - Chunyu Guo
- Center for Correlated Matter, Zhejiang University, Hangzhou 310058, People’s Republic of China
- Department of Physics, Zhejiang University, Hangzhou 310058, People’s Republic of China
| | - Huiqiu Yuan
- Center for Correlated Matter, Zhejiang University, Hangzhou 310058, People’s Republic of China
- Department of Physics, Zhejiang University, Hangzhou 310058, People’s Republic of China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, People’s Republic of China
| | - Chao-Xing Liu
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Zachary Fisk
- Department of Physics and Astronomy, University of California, Irvine, CA 92697, USA
| | - Frank Steglich
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany
- Center for Correlated Matter, Zhejiang University, Hangzhou 310058, People’s Republic of China
- Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
| | - Steffen Wirth
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany
| |
Collapse
|
21
|
Demishev SV, Gilmanov MI, Samarin AN, Semeno AV, Sluchanko NE, Samarin NA, Bogach AV, Shitsevalova NY, Filipov VB, Karasev MS, Glushkov VV. Magnetic resonance probing of ground state in the mixed valence correlated topological insulator SmB 6. Sci Rep 2018; 8:7125. [PMID: 29740044 PMCID: PMC5940907 DOI: 10.1038/s41598-018-25464-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2018] [Accepted: 04/20/2018] [Indexed: 11/09/2022] Open
Abstract
Introducing of topological insulator concept for fluctuating valence compound - samarium hexaboride - has recently initiated a new round of studies aimed to clarify the nature of the ground state in this extraordinary system with strong electron correlations. Here we discuss the data of magnetic resonance in the pristine single crystals of SmB6 measured in 60 GHz cavity experiments at temperatures 1.8-300 K. The microwave study as well as the DC resistivity and Hall effect measurements performed for the different states of SmB6 [110] surface prove definitely the existence of the layer with metallic conductivity increasing under lowering temperature below 5 K. Four lines with the g-factors g ≈ 2 are found to contribute to the ESR-like absorption spectrum that may be attributed to intrinsic paramagnetic centers on the sample's surface, which are robust with respect to the surface treatment. The temperature dependence of integrated intensity I(T) for main paramagnetic signal is found to demonstrate anomalous critical behavior I(T) ~ (T* - T)ν with characteristic temperature T * = 5.34 ± 0.05 K and exponent ν = 0.38 ± 0.03 indicating possible magnetic transition at the SmB6 [110] surface. Additional resonant magnetoabsorption line, which may be associated with either donor-like defects or cyclotron resonance mode corresponding to the mass m c ~ 1.2m0, is reported.
Collapse
Affiliation(s)
- S V Demishev
- Moscow Institute of Physics and Technology, Dolgoprudny, 141700, Moscow region, Russia.,National Research University Higher School of Economics, Moscow, 101000, Russia
| | - M I Gilmanov
- Moscow Institute of Physics and Technology, Dolgoprudny, 141700, Moscow region, Russia.,Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, 119991, Russia
| | - A N Samarin
- Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, 119991, Russia
| | - A V Semeno
- Moscow Institute of Physics and Technology, Dolgoprudny, 141700, Moscow region, Russia.,Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, 119991, Russia
| | - N E Sluchanko
- Moscow Institute of Physics and Technology, Dolgoprudny, 141700, Moscow region, Russia.,Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, 119991, Russia
| | - N A Samarin
- Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, 119991, Russia
| | - A V Bogach
- Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, 119991, Russia
| | - N Yu Shitsevalova
- Institute for Problems of Materials Science of NASU, Kiev, 03680, Ukraine
| | - V B Filipov
- Institute for Problems of Materials Science of NASU, Kiev, 03680, Ukraine
| | - M S Karasev
- Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, 119991, Russia
| | - V V Glushkov
- Moscow Institute of Physics and Technology, Dolgoprudny, 141700, Moscow region, Russia. .,Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, 119991, Russia.
| |
Collapse
|
22
|
Jiao L, Rößler S, Kim DJ, Tjeng LH, Fisk Z, Steglich F, Wirth S. Additional energy scale in SmB 6 at low-temperature. Nat Commun 2016; 7:13762. [PMID: 27941948 PMCID: PMC5159841 DOI: 10.1038/ncomms13762] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2016] [Accepted: 10/31/2016] [Indexed: 11/09/2022] Open
Abstract
Topological insulators give rise to exquisite electronic properties because of their spin-momentum locked Dirac-cone-like band structure. Recently, it has been suggested that the required opposite parities between valence and conduction band along with strong spin-orbit coupling can be realized in correlated materials. Particularly, SmB6 has been proposed as candidate material for a topological Kondo insulator. Here we observe, by utilizing scanning tunnelling microscopy and spectroscopy down to 0.35 K, several states within the hybridization gap of about ±20 meV on well characterized (001) surfaces of SmB6. The spectroscopic response to impurities and magnetic fields allows to distinguish between dominating bulk and surface contributions to these states. The surface contributions develop particularly strongly below about 7 K, which can be understood in terms of a suppressed Kondo effect at the surface. Our high-resolution data provide insight into the electronic structure of SmB6, which reconciles many current discrepancies on this compound.
Collapse
Affiliation(s)
- L. Jiao
- Max-Planck-Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
| | - S. Rößler
- Max-Planck-Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
| | - D. J. Kim
- Department of Physics and Astronomy, University of California, Irvine, CA 92697, USA
| | - L. H. Tjeng
- Max-Planck-Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
| | - Z. Fisk
- Department of Physics and Astronomy, University of California, Irvine, CA 92697, USA
| | - F. Steglich
- Max-Planck-Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
- Center for Correlated Matter, Zhejiang University, Hangzhou 310058, China
- Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - S. Wirth
- Max-Planck-Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
| |
Collapse
|
23
|
Surface Kondo effect and non-trivial metallic state of the Kondo insulator YbB12. Nat Commun 2016; 7:12690. [PMID: 27576449 PMCID: PMC5515356 DOI: 10.1038/ncomms12690] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2016] [Accepted: 07/21/2016] [Indexed: 11/28/2022] Open
Abstract
A synergistic effect between strong electron correlation and spin–orbit interaction has been theoretically predicted to realize new topological states of quantum matter on Kondo insulators (KIs), so-called topological Kondo insulators (TKIs). One TKI candidate has been experimentally observed on the KI SmB6(001), and the origin of the surface states (SS) and the topological order of SmB6 has been actively discussed. Here, we show a metallic SS on the clean surface of another TKI candidate YbB12(001) using angle-resolved photoelectron spectroscopy. The SS shows temperature-dependent reconstruction corresponding to the Kondo effect observed for bulk states. Despite the low-temperature insulating bulk, the reconstructed SS with c–f hybridization is metallic, forming a closed Fermi contour surrounding on the surface Brillouin zone and agreeing with the theoretically expected behaviour for SS on TKIs. These results demonstrate the temperature-dependent holistic reconstruction of two-dimensional states localized on KIs surface driven by the Kondo effect. Topological state in Kondo insulators has been provoked in SmB6, but the origin of surface states and topological order remain elusive. Here, Hagiwara et al. report temperature dependent reconstruction of a metallic surface state on the (001) surface of YbB12 driven by Kondo effect and discuss its origin from topology.
Collapse
|