Interacting fermions in narrow-gap semiconductors with band inversion

TL;DR

This paper investigates many-body instabilities in narrow-gap semiconductors with band inversion, revealing a stable excitonic instability with time-reversal symmetry breaking under certain conditions using renormalization group analysis.

Contribution

It introduces a low-energy theory for interacting particles in band-inverted narrow-gap semiconductors and identifies conditions for excitonic instability via renormalization group techniques.

Findings

Identifies a stable fixed point for excitonic instability.

Shows the role of effective mass mismatch in symmetry breaking.

Provides theoretical insight into thermodynamic anomalies in samarium hexaboride.

Abstract

Highly unconventional behavior of the thermodynamic response functions has been experimentally observed in a narrow gap semiconductor samarium hexaboride. Motivated by these observations, we use renormalization group technique to investigate many-body instabilities in the f-orbital narrow gap semiconductors with band inversion in the limit of weak coupling. After projecting out the double occupancy of the f-orbital states, we formulate a low-energy theory describing the interacting particles in two hybridized electron- and hole-like bands. The interactions are assumed to be weak and short-ranged. We take into account the difference between the effective masses of the quasiparticles in each band. Upon carrying out the renormalization group analysis we find that there is only one stable fixed point corresponding to the excitonic instability with time-reversal symmetry breaking for small enough mismatch between the effective masses.