Search for magnetoacoustic quantum oscillations in the insulating phase of YbB$_{12}$

TL;DR

This study used ultrasonic experiments to search for magnetoacoustic quantum oscillations in the insulator YbB$_{12}$ under high magnetic fields, finding oscillations only in the metallic state and revealing anomalies in the insulating state.

Contribution

The paper provides the first ultrasonic evidence that magnetoacoustic quantum oscillations are absent in the insulating phase of YbB$_{12}$, clarifying previous conflicting observations.

Findings

Oscillations observed in the metallic state of YbB$_{12}$.

No magnetoacoustic quantum oscillations detected in the insulating state.

Ultrasound data revealed anomalies in the insulating phase whose origin remains unknown.

Abstract

A highly exotic phenomenon in solid-state physics is the observation of magnetic quantum oscillations in insulators. For instance, in the Kondo insulator YbB$_{12}$ various groups reported the observation of such oscillations seemingly originating from Fermi surfaces, though this contradicts the concept of an insulator having no charged quasiparticles. In this study, we searched for quantum oscillations in YbB$_{12}$ by using bulk-sensitive ultrasonic experiments in high magnetic fields up to 65 T and down to 485 mK. For that, we utilized an YbB$_{12}$ single crystal that, in previous experiments, revealed oscillations in the magnetoresistance in the insulating state. We confirmed oscillation-like behavior of the magnetoresistance as well as field-dependent oscillations in the magnetocaloric effect. However, we could not observe magnetoacoustic quantum oscillations in the insulating state, only in the field-induced metallic state. In the insulating state, we found some anomalies in our ultrasound data, the origin of which remains elusive. Our findings provide further information on the puzzling behavior of the insulating state of YbB$_{12}$.