Reduction of the low-temperature bulk gap in samarium hexaboride under high magnetic fields

TL;DR

This study investigates how high magnetic fields affect the bulk energy gap in samarium hexaboride, revealing a significant reduction in the gap and challenging existing theories about magnetic quantum oscillations.

Contribution

It provides experimental evidence that the bulk gap in SmB$_6$ shrinks under high magnetic fields, contradicting previous explanations of magnetic quantum oscillations.

Findings

Bulk gap shrinks by 50% at 60 T

Surface states remain nearly temperature-independent

Data suggests gap reduction continues beyond 100 T

Abstract

SmB$_6$ exhibits a small (15-20 meV) bandgap at low temperatures due to hybridized $d$ and $f$ electrons, a tiny (3 meV) transport activation energy $(E_{A})$ above 4 K, and surface states accessible to transport below 2 K. We study its magnetoresistance in 60-T pulsed fields between 1.5 K and 4 K. The response of the nearly $T$-independent surface states (which show no Shubnikov-de Haas oscillations) is distinct from that of the activated bulk. $E_{A}$ shrinks by 50% under fields up to 60 T. Data up to 93 T suggest that this trend continues beyond 100 T, in contrast with previous explanations. It rules out emerging theories to explain observed exotic magnetic quantum oscillations.