Unconventional Fermi surface in an insulating state

TL;DR

This paper reports the discovery of an insulating state in SmB6 that exhibits quantum oscillations indicative of a Fermi surface, challenging traditional distinctions between insulators and metals.

Contribution

It provides evidence of an unconventional Fermi liquid-like behavior in an insulator, revealing a novel electronic state in a topological Kondo insulator.

Findings

Observation of quantum oscillations in an insulator

Detection of a large 3D Fermi surface in SmB6

Amplitude increase of oscillations at low temperatures

Abstract

Insulators occur in more than one guise, a recent finding was a class of topological insulators, which host a conducting surface juxtaposed with an insulating bulk. Here we report the observation of an unusual insulating state with an electrically insulating bulk that simultaneously yields bulk quantum oscillations with characteristics of an unconventional Fermi liquid. We present quantum oscillation measurements of magnetic torque in high purity single crystals of the Kondo insulator SmB6, which reveal quantum oscillation frequencies characteristic of a large three-dimensional conduction electron Fermi surface similar to the metallic rare earth hexaborides such as PrB6 and LaB6. The quantum oscillation amplitude strongly increases at low temperatures, appearing strikingly at variance with conventional metallic behaviour.