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Dynamical Bonding Driving Mixed Valency in a Metal Boride
Author(s) -
Robinson Paul J.,
Munarriz Julen,
Valentine Michael E.,
Granmoe Austin,
Drichko Natalia,
Chamorro Juan R.,
Rosa Priscila F.,
McQueen Tyrel M.,
Alexandrova Anastassia N.
Publication year - 2020
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.202000945
Subject(s) - valency , valence (chemistry) , condensed matter physics , fermi surface , raman spectroscopy , materials science , chemistry , physics , quantum mechanics , philosophy , linguistics , superconductivity
Samarium hexaboride is an anomaly, having many exotic and seemingly mutually incompatible properties. It was proposed to be a mixed‐valent semiconductor, and later a topological Kondo insulator, and yet has a Fermi surface despite being an insulator. We propose a new and unified understanding of SmB 6 centered on the hitherto unrecognized dynamical bonding effect: the coexistence of two Sm−B bonding modes within SmB 6 , corresponding to different oxidation states of the Sm. The mixed valency arises in SmB 6 from thermal population of these distinct minima enabled by motion of B. Our model simultaneously explains the thermal valence fluctuations, appearance of magnetic Fermi surface, excess entropy at low temperatures, pressure‐induced phase transitions, and related features in Raman spectra and their unexpected dependence on temperature and boron isotope.