Robinson Paul J, Munarriz Julen, Valentine Michael E, Granmoe Austin, Drichko Natalia, Chamorro Juan R, Rosa Priscila F, McQueen Tyrel M, Alexandrova Anastassia N
Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, CA, 90095, USA.
Current Address: Department of Chemistry, Columbia University, New York, NY, 10027, USA.
Angew Chem Int Ed Engl. 2020 Jun 26;59(27):10996-11002. doi: 10.1002/anie.202000945. Epub 2020 Apr 6.
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 centered on the hitherto unrecognized dynamical bonding effect: the coexistence of two Sm-B bonding modes within SmB , corresponding to different oxidation states of the Sm. The mixed valency arises in SmB 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.
六硼化钐是一种异类物质，具有许多奇特且看似相互矛盾的性质。它曾被认为是一种混合价半导体，后来又被认定为拓扑近藤绝缘体，然而尽管它是绝缘体，却拥有费米面。我们提出了一种对六硼化钐全新的统一理解，其核心是迄今未被认识到的动态键合效应：在六硼化钐中存在两种Sm-B键合模式，对应于Sm的不同氧化态。六硼化钐中的混合价态源于硼原子运动使得这些不同的能量极小值发生热占据。我们的模型同时解释了热价态涨落、磁性费米面的出现、低温下的过剩熵、压力诱导的相变以及拉曼光谱中的相关特征及其对温度和硼同位素的意外依赖性。
