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| Samarium hexaboride | |
|---|---|
| Name | Samarium hexaboride |
| Othernames | SmB6 |
| Formula | SmB6 |
| Appearance | metallic gray crystalline |
Samarium hexaboride is an inorganic compound studied as a correlated electron material and candidate topological Kondo insulator, attracting attention from researchers at institutions such as Lawrence Berkeley National Laboratory, Max Planck Institute for Chemical Physics of Solids, Princeton University, Stanford University, and University of California, Berkeley. Originally synthesized and characterized in the context of rare-earth borides by groups including John Wiley & Sons-era solid state chemists and industrial laboratories like Bell Labs, it has been the subject of experimental campaigns involving collaborations with facilities such as Oak Ridge National Laboratory, Argonne National Laboratory, CERN, Paul Scherrer Institute, and Brookhaven National Laboratory.
Samarium hexaboride is a cubic rare-earth boride notable for its mixed-valence samarium, narrow-gap insulating behavior at low temperatures, and surface conduction phenomena explored by teams from Harvard University, Massachusetts Institute of Technology, Columbia University, Yale University, and University of Cambridge. Debates over its classification as a topological insulator engaged theorists connected to Princeton University, University of Illinois Urbana-Champaign, California Institute of Technology, University of Tokyo, and Institute for Advanced Study, while experimentalists at Los Alamos National Laboratory, University of Oxford, ETH Zurich, National Institute of Standards and Technology, and RIKEN probed its anomalous transport and spectroscopic signatures.
Samarium hexaboride crystallizes in the cubic CaB6-type structure (space group Pm-3m) with samarium atoms at cube corners and rigid boron octahedra forming a three-dimensional network; early structural determinations were published by researchers associated with American Physical Society, Royal Society, Deutsche Physikalische Gesellschaft, Journal of Solid State Chemistry, and Nature Materials-affiliated groups. Single crystals are commonly grown by the floating-zone method, flux growth, and zone refining techniques developed at laboratories including Hitachi, Toshiba, Mitsubishi Heavy Industries, Furukawa Electric, and university crystal growth facilities linked to University of Minnesota. Synthesis protocols often reference starting materials and procedures refined by teams at Sumitomo Chemical, Johnson Matthey, Alfa Aesar, Sigma-Aldrich, and specialized facilities in collaboration with French Alternative Energies and Atomic Energy Commission and National Research Council (Canada).
The bulk material exhibits a temperature-dependent crossover from metallic to insulating behavior below roughly 50 K, with a hybridization gap on the order of a few to tens of meV reported by groups at IBM Research, Microsoft Research, Google Research, Facebook AI Research, and academic condensed matter laboratories. Magnetic susceptibility reflects mixed-valence samarium (Sm2+/Sm3+) and has been characterized by neutron scattering and muon spin rotation teams at ISIS Neutron and Muon Source, Institut Laue-Langevin, Spallation Neutron Source, and TRIUMF. Thermal conductivity, specific heat, and elastic properties have been measured by consortia involving Max Planck Society, European Synchrotron Radiation Facility, Deutsches Elektronen-Synchrotron, Diamond Light Source, and SPring-8.
The electronic structure involves strong f-d hybridization between samarium 4f and conduction 5d bands, with theoretical descriptions developed by researchers affiliated with David J. Scalapino, Piers Coleman, Philip W. Anderson, Alexei M. Tsvelik, and groups at University of California, Santa Barbara. First-principles calculations and dynamical mean-field theory studies from teams at Rutgers University, University of Notre Dame, Imperial College London, University of St Andrews, and University of British Columbia addressed band inversion and nontrivial topology, motivating spectroscopic efforts by investigators at Stanford Synchrotron Radiation Lightsource, Japan Synchrotron Radiation Research Institute, Paul Scherrer Institute, Brookhaven National Laboratory and MAX IV Laboratory.
Transport measurements reveal a low-temperature plateau in resistivity attributed to surface conduction channels while the bulk becomes Kondo-insulating; landmark electrical and thermal transport studies involved collaborations among Bell Labs, Los Alamos National Laboratory, Argonne National Laboratory, University of Michigan, and University of Chicago. Hall effect, magnetoresistance, and quantum oscillation experiments by teams at National High Magnetic Field Laboratory, Laboratoire National des Champs Magnétiques Intenses, High Field Magnet Laboratory, Weizmann Institute of Science, and Southampton probed itinerant carriers and possible two-dimensional surface states, engaging theorists from Mikhail V. Feigelman, Andrey Chubukov, Elihu Abrahams, and Subir Sachdev in interpreting emergent behavior.
Angle-resolved photoemission spectroscopy (ARPES), scanning tunneling microscopy (STM), neutron scattering, Raman spectroscopy, infrared and terahertz spectroscopy, and X-ray absorption studies have been pursued by teams at SLAC National Accelerator Laboratory, Lawrence Livermore National Laboratory, Brookhaven National Laboratory, Diamond Light Source, and European XFEL. ARPES groups from University of California, Los Angeles, Paul Scherrer Institute, University of Bristol, National University of Singapore, and Zhejiang University reported surface state dispersions and hybridization gaps, while STM efforts by researchers at Cornell University, University of Geneva, University of Warwick, Tokyo Institute of Technology, and Kavli Institute explored spatial inhomogeneity and Kondo resonances. Muon spin rotation and nuclear magnetic resonance experiments from TRIUMF, ISIS, Los Alamos, Rutherford Appleton Laboratory, and Canadian Light Source provided complementary insights into magnetic fluctuations and low-energy excitations.
Potential applications envisioned by multidisciplinary teams at Hitachi, NEC Corporation, Panasonic, Siemens, Schneider Electric, and academic startups include robust low-temperature surface conduction elements for spintronics, quantum devices, and metrological standards; proposals intersect with research at Microsoft Quantum, IBM Quantum, D-Wave Systems, Intel Labs, and European Commission-funded consortia. Integration challenges and device concepts have been discussed in collaborations between Stanford University, Massachusetts Institute of Technology, National Institute of Advanced Industrial Science and Technology, Tsinghua University, and Peking University.
Category:Samarium compounds