Properties of the donor impurity band in mixed valence insulators

Abstract

In traditional semiconductors with large effective Bohr radius, an electron donor creates a hydrogen-like bound state just below the conduction band edge. The properties of the impurity band arising from such hydrogenic impurities have been studied extensively during the last 70 years. In this paper we consider whether a similar bound state and a similar impurity band can exist in mixed-valence insulators, where the gap arises at low temperature due to strong electron-electron interactions. We find that the structure of the hybridized conduction band leads to an unusual bound state that can be described using the physics of the one-dimensional hydrogen atom. The properties of the resulting impurity band are also modified in a number of ways relative to the traditional semiconductor case; most notably, the impurity band can hold a much larger concentration without inducing an insulator-to-metal transition. We estimate the critical doping associated with this transition, and then proceed to calculate the dc and ac conductivities and the specific heat. We discuss our results in light of recent measurements on the mixed-valence insualtor SmB${}_6$, and find them to be consistent with the experiments.

9+5 pages, 3 figures; published version

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• Hall anomaly, Quantum Oscillations and Possible Lifshitz Transitions in Kondo Insulator YbB${}_{12}$: Evidence for Unconventional Charge Transport
• Intrinsic Low-Temperature Magnetism in SmB6
• Bulk transport paths through defects in floating zone and Al flux grown SmB${}_6$
• Extraordinary Bulk Insulating Behavior in the Strongly Correlated Materials FeSi and FeSb${}_2$
• Robust surface states and coherence phenomena in magnetically alloyed SmB6
• Shadow surface states in topological Kondo insulators
• Correlated Topological Mixed-Valence Insulators in Moiré Hetero-Bilayers
• Fluctuation-dominated quantum oscillations in excitonic insulators
• Quantum Oscillations in an Impurity-Band Anderson Insulator
• Chiral Wigner crystal phases induced by Berry curvature
• The Future of the Correlated Electron Problem
• A Mean-Field Study of Quantum Oscillations in Two-Dimensional Kondo Insulators
• Mapping out the emergence of topological features in the highly alloyed topological Kondo insulators Sm${}_{1-x}{M}_x$B${}_6$ ($M$=Eu, Ce)