1
|
Pirie H, Mascot E, Matt CE, Liu Y, Chen P, Hamidian MH, Saha S, Wang X, Paglione J, Luke G, Goldhaber-Gordon D, Hirjibehedin CF, Davis JCS, Morr DK, Hoffman JE. Visualizing the atomic-scale origin of metallic behavior in Kondo insulators. Science 2023; 379:1214-1218. [PMID: 36952423 DOI: 10.1126/science.abq5375] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/25/2023]
Abstract
A Kondo lattice is often electrically insulating at low temperatures. However, several recent experiments have detected signatures of bulk metallicity within this Kondo insulating phase. In this study, we visualized the real-space charge landscape within a Kondo lattice with atomic resolution using a scanning tunneling microscope. We discovered nanometer-scale puddles of metallic conduction electrons centered around uranium-site substitutions in the heavy-fermion compound uranium ruthenium silicide (URu2Si2) and around samarium-site defects in the topological Kondo insulator samarium hexaboride (SmB6). These defects disturbed the Kondo screening cloud, leaving behind a fingerprint of the metallic parent state. Our results suggest that the three-dimensional quantum oscillations measured in SmB6 arise from Kondo-lattice defects, although we cannot exclude other explanations. Our imaging technique could enable the development of atomic-scale charge sensors using heavy-fermion probes.
Collapse
Affiliation(s)
- Harris Pirie
- Department of Physics, Harvard University, Cambridge, MA 02138, USA
- Clarendon Laboratory, University of Oxford, Oxford OX1 3PU, UK
| | - Eric Mascot
- Department of Physics, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Christian E Matt
- Department of Physics, Harvard University, Cambridge, MA 02138, USA
| | - Yu Liu
- Department of Physics, Harvard University, Cambridge, MA 02138, USA
| | - Pengcheng Chen
- Department of Physics, Harvard University, Cambridge, MA 02138, USA
| | - M H Hamidian
- Department of Physics, Harvard University, Cambridge, MA 02138, USA
| | - Shanta Saha
- Maryland Quantum Materials Center, Department of Physics, University of Maryland, College Park, MD 20742, USA
| | - Xiangfeng Wang
- Maryland Quantum Materials Center, Department of Physics, University of Maryland, College Park, MD 20742, USA
| | - Johnpierre Paglione
- Maryland Quantum Materials Center, Department of Physics, University of Maryland, College Park, MD 20742, USA
| | - Graeme Luke
- Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1, Canada
| | - David Goldhaber-Gordon
- Department of Physics, Stanford University, Stanford, CA 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
| | - Cyrus F Hirjibehedin
- London Centre for Nanotechnology, University College London (UCL), London WC1H 0AH, UK
- Department of Physics and Astronomy, UCL, London WC1E 6BT, UK
- Department of Chemistry, UCL, London WC1H 0AJ, UK
| | - J C Séamus Davis
- Clarendon Laboratory, University of Oxford, Oxford OX1 3PU, UK
- Department of Physics, University College Cork, Cork T12 R5C, Ireland
- Laboratory of Atomic and Solid State Physics, Department of Physics, Cornell University, Ithaca, NY 14850, USA
- Max Planck Institute for Chemical Physics of Solids, D-01187 Dresden, Germany
| | - Dirk K Morr
- Department of Physics, University of Illinois at Chicago, Chicago, IL 60607, USA
| | | |
Collapse
|
2
|
Aamlid SS, Oudah M, Rottler J, Hallas AM. Understanding the Role of Entropy in High Entropy Oxides. J Am Chem Soc 2023; 145:5991-6006. [PMID: 36881986 DOI: 10.1021/jacs.2c11608] [Citation(s) in RCA: 13] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/09/2023]
Abstract
The field of high entropy oxides (HEOs) flips traditional materials science paradigms on their head by seeking to understand what properties arise in the presence of profound configurational disorder. This disorder, which originates from multiple elements sharing a single lattice site, can take on a kaleidoscopic character due to the vast numbers of possible elemental combinations. High configurational disorder appears to imbue some HEOs with functional properties that far surpass their nondisordered analogs. While experimental discoveries abound, efforts to characterize the true magnitude of the configurational entropy and understand its role in stabilizing new phases and generating superior functional properties have lagged behind. Understanding the role of configurational disorder in existing HEOs is the crucial link to unlocking the rational design of new HEOs with targeted properties. In this Perspective, we attempt to establish a framework for articulating and beginning to address these questions in pursuit of a deeper understanding of the true role of entropy in HEOs.
Collapse
Affiliation(s)
- Solveig S Aamlid
- Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, BC V6T 1Z4, Canada
| | - Mohamed Oudah
- Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, BC V6T 1Z4, Canada
| | - Jörg Rottler
- Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, BC V6T 1Z4, Canada
- Department of Physics & Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
| | - Alannah M Hallas
- Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, BC V6T 1Z4, Canada
- Department of Physics & Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
| |
Collapse
|
3
|
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
|
4
|
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
|
5
|
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
|
6
|
Xu D, Gao S, Liu W, Liu Y, Zhou Q, Li L, Cui T, Yuan H. The Raman scattering of trirutile structure MgTa 2O 6 single crystals grown by the optical floating zone method. RSC Adv 2019; 9:839-843. [PMID: 35517588 PMCID: PMC9059477 DOI: 10.1039/c8ra06113k] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2018] [Accepted: 11/26/2018] [Indexed: 11/30/2022] Open
Abstract
Single crystals of the trirutile structure MgTa2O6 were grown via an optical floating zone method in an air atmosphere. The as-grown crystals were pale yellow and transparent and the natural cleavage plane formed during the crystal growth was determined by XRD2 to be along the c-axis direction. The variations in valence were investigated by XPS (X-ray photoelectron spectroscopy). The room-temperature axis-relative polarized Raman spectra of trirutile MgTa2O6 crystals were described. The order–disorder effect was detected via temperature-dependent Raman spectroscopy. Single crystals of the trirutile structure MgTa2O6 were grown via an optical floating zone method in an air atmosphere.![]()
Collapse
Affiliation(s)
- Dapeng Xu
- State Key Laboratory of Superhard Materials, College of Physics, Jilin University Changchun Jilin China
| | - Shuohui Gao
- China-Japan Union Hospital of Jilin University Changchun 130000 P. R. China
| | - Wenqiang Liu
- State Key Laboratory of Superhard Materials, College of Physics, Jilin University Changchun Jilin China .,College of Physics, Harbin Institute of Technology Harbin Heilongjiang China
| | - Ying Liu
- State Key Laboratory of Superhard Materials, College of Physics, Jilin University Changchun Jilin China
| | - Qiang Zhou
- State Key Laboratory of Superhard Materials, College of Physics, Jilin University Changchun Jilin China
| | - Liang Li
- State Key Laboratory of Superhard Materials, College of Physics, Jilin University Changchun Jilin China .,College of Mechanical Engineering, University of Texas at Austin Austin Texas USA
| | - Tian Cui
- State Key Laboratory of Superhard Materials, College of Physics, Jilin University Changchun Jilin China
| | - Hongming Yuan
- State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University Changchun Jilin China
| |
Collapse
|
7
|
Fuhrman WT, Chamorro JR, Alekseev PA, Mignot JM, Keller T, Rodriguez-Rivera JA, Qiu Y, Nikolić P, McQueen TM, Broholm CL. Screened moments and extrinsic in-gap states in samarium hexaboride. Nat Commun 2018; 9:1539. [PMID: 29670117 PMCID: PMC5906653 DOI: 10.1038/s41467-018-04007-z] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2017] [Accepted: 03/27/2018] [Indexed: 11/20/2022] Open
Abstract
Samarium hexaboride (SmB6) is a Kondo insulator, with a narrow gap due to hybridization between localized and conduction electrons. Despite being an insulator, many samples show metal-like properties. Rare-earth purification is exceedingly difficult, and nominally pure samples may contain 2% or more of impurities. Here to determine the effects of rare-earth doping on SmB6, we synthesized and probed a series of gadolinium-doped samples. We found a relationship between specific heat and impurity moment screening which scales systematically. Consistent with this finding, our neutron scattering experiments of a high purity sample of doubly isotopic 154Sm11B6 show no intrinsic excitations below the well-established 13 meV spin-exciton. The result of introducing impurities into a Kondo insulator is incompletely understood, but it is clear from our measurements that there is a systematic relationship between rare-earth impurities and metal-like properties in SmB6. The unconventional behaviour of samarium hexaboride has been difficult to explain in part because of differences between samples. Here the authors use gadolinium to exemplify that hard to avoid impurities introduce a low energy density of states that may explain earlier observations.
Collapse
Affiliation(s)
- W T Fuhrman
- Institute for Quantum Matter and Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD, 21218, USA.
| | - J R Chamorro
- Institute for Quantum Matter and Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD, 21218, USA.,Department of Chemistry, The Johns Hopkins University, Baltimore, MD, 21218, USA
| | - P A Alekseev
- National Research Centre "Kurchatov Institute", 123182, Moscow, Russia.,National Research Nuclear University "MEPhI", 115409, Moscow, Russia
| | - J-M Mignot
- Laboratoire Léon Brillouin, CEA-CNRS, CEA/Saclay, 91191, Gif sur Yvette, France
| | - T Keller
- Max Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569, Stuttgart, Germany.,Max Planck Society at the Forschungsneutronenquelle Heinz Maier-Leibnitz (MLZ), D-85747, Garching, Germany
| | - J A Rodriguez-Rivera
- Department of Materials Sciences, University of Maryland, College Park, MD, 20742, USA.,NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, 20899, USA
| | - Y Qiu
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, 20899, USA
| | - P Nikolić
- Institute for Quantum Matter and Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD, 21218, USA.,School of Physics, Astronomy and Computational Sciences, George Mason University, Fairfax, VA, 22030, USA
| | - T M McQueen
- Institute for Quantum Matter and 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
| | - C L Broholm
- Institute for Quantum Matter and Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD, 21218, USA.,Department of Materials Science and Engineering, The Johns Hopkins University, Baltimore, MD, 21218, USA
| |
Collapse
|
8
|
Kohlmann H, Hein C, Kautenburger R, Hansen TC, Ritter C, Doyle S. Crystal structure of monoclinic samarium and cubic europium sesquioxides and bound coherent neutron scattering lengths of the isotopes 154Sm and 153Eu. Z KRIST-CRYST MATER 2016. [DOI: 10.1515/zkri-2016-1984] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Abstract
The crystal structures of monoclinic samarium and cubic europium sesquioxide, Sm2O3 and Eu2O3, were reinvestigated by powder diffraction methods (laboratory X-ray, synchrotron, neutron). Rietveld analysis yields more precise structural parameters than previously known, especially for oxygen atoms. Interatomic distances d(Sm–O) in Sm2O3 range from 226.3(4) to 275.9(2) pm [average 241.6(3) pm] for the monoclinic B type Sm2O3 [space group C2/m, a = 1418.04(3) pm, b = 362.660(7) pm, c = 885.48(2) pm, β = 100.028(1)°], d(Eu–O) in Eu2O3 from 229.9(2) to 238.8(2) pm for the cubic bixbyite (C) type [space group Ia3̅, a = 1086.87(1) pm]. Neutron diffraction at 50 K and 2 K did not show any sign for magnetic ordering in Sm2O3. Isotopically enriched 154Sm2O3 and 153Eu2O3 were used for the neutron diffraction work because of the enormous absorption cross section of the natural isotopic mixtures for thermal neutrons. The isotopic purity was determined by inductively coupled plasma – mass spectrometry to be 98.9% for 154Sm and 99.8% for 153Eu. Advanced analysis of the neutron diffraction data suggest that the bound coherent scattering lengths of 154Sm and 153Eu need to be revised. We tentatively propose b
c(154Sm) = 8.97(6) fm and b
c(153Eu) = 8.85(3) fm for a neutron wavelength of 186.6 pm to be better values for these isotopes, showing up to 8% deviation from accepted literature values. It is shown that inaccurate scattering lengths may result in severe problems in crystal structure refinements causing erroneous structural details such as occupation parameters, which might be critically linked to physical properties like superconductivity in multinary oxides.
Collapse
Affiliation(s)
- Holger Kohlmann
- Institute of Inorganic Chemistry, University Leipzig, Johannisallee 29, 04103 Leipzig, Germany
| | - Christina Hein
- Inorganic Solid State Chemistry, Saarland University, P.O. Box 151150, 66041 Saarbrücken, Germany
| | - Ralf Kautenburger
- Inorganic Solid State Chemistry, Saarland University, P.O. Box 151150, 66041 Saarbrücken, Germany
| | - Thomas C. Hansen
- Institut Laue-Langevin, 71 avenue des Martyrs, 38000 Grenoble, France
| | - Clemens Ritter
- Institut Laue-Langevin, 71 avenue des Martyrs, 38000 Grenoble, France
| | - Stephen Doyle
- Karlsruhe Institute of Technology, Institute for Synchrotron Radiation (ISS), Hermann-v.-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
| |
Collapse
|