Absence of metallicity and bias-dependent resistivity in low-carrier-density EuCd2As2

TL;DR

This study reveals that high-quality EuCd2As2 crystals with ultralow carrier density exhibit insulating behavior and nonlinear transport phenomena, challenging the expectation of Weyl semimetal characteristics in this material.

Contribution

The paper provides the first comprehensive magneto-transport analysis of EuCd2As2 with ultralow carrier density, showing insulating behavior and nonlinear effects contrary to prior predictions.

Findings

EuCd2As2 shows insulating behavior in both magnetic states.

Application of bias current induces large resistance modulation and oscillations.

Results suggest an insulating phase, constraining Weyl semimetal models.

Abstract

EuCd2As2 was theoretically predicted to be a minimal model of Weyl semimetals with a single pair of Weyl points in the ferromagnet state. However, the heavily p-doped EuCd2As2 crystals in previous experiments prevent direct identification of the semimetal hypothesis. Here we present a comprehensive magneto-transport study of high-quality EuCd2As2 crystals with ultralow bulk carrier density (10^13 cm-3). In contrast to the general expectation of a Weyl semimetal phase, EuCd2As2 shows insulating behavior in both antiferromagnetic and ferromagnetic states as well as surface-dominated conduction from band bending. Moreover, the application of a dc bias current can dramatically modulate the resistance by over one order of magnitude, and induce a periodic resistance oscillation due to the geometric resonance. Such nonlinear transport results from the highly nonequilibrium state induced by electrical field near the band edge. Our results suggest an insulating phase in EuCd2As2 and put a strong constraint on the underlying mechanism of anomalous transport properties in this system.