Impedance Spectroscopy of SmB$_6$ single crystals

TL;DR

This study investigates the low-temperature impedance behavior of SmB$_6$ single crystals, revealing a universal circuit model, temperature-dependent inductance, and nonlinear effects like negative differential resistance and voltage oscillations.

Contribution

It introduces a universal equivalent circuit model for SmB$_6$ impedance across the surface-bulk transition and analyzes the temperature-dependent electrical contributions and nonlinear phenomena.

Findings

Universal impedance behavior described by an equivalent circuit.

Inductive contribution drops as bulk conduction dominates.

Observation of negative differential resistance and voltage oscillations.

Abstract

We report results from an in--plane and out--of--plane impedance study on SmB$_6$ single crystals, performed at low temperatures and over a wide frequency range. A universal equivalent circuit describes the dielectric behavior of this system across the transition, from surface to bulk dominated electrical conduction between 2 and 10 K. We identify the resistive, capacitive, and inductive contributions to the impedance. The equivalent inductance, obtained from fits to experimental data, drops drastically as the bulk starts to control electrical conduction upon increasing temperature. SmB$_6$ single crystals also show current--controlled negative differential resistance at low temperatures, which is brought about by Joule heating. This feature, in addition to inductive and capacitive contributions to the impedance, can give rise to the self--sustained voltage oscillations observed below 5 K (Stern {\it et al.}, Phys. Rev. Lett. {\bf 116}, 166603 (2016)).