Metamagnetic quantum criticality in the antiferromagnetic topological insulator MnBi$_2$Te$_4$

TL;DR

This study uncovers a tricritical point and quantum critical endpoints in the magnetic phase diagram of MnBi$_2$Te$_4$, a topological insulator, revealing complex magnetic phase transitions driven by magnetic field.

Contribution

It reports the discovery of a tricritical point and quantum critical endpoints in MnBi$_2$Te$_4$, highlighting novel magnetic phase behavior in a topological insulator.

Findings

Identification of a tricritical point connecting magnetic phases.

Observation of bifurcating phase boundaries under magnetic field.

Detection of quantum critical endpoints at high fields.

Abstract

Combining transport and magnetization measurements, we discover the emergence of a tricritical point connecting the antiferromagnetic, metamagnetic and paramagnetic regions in MnBi$_2$Te$_4$, a magnetic topological insulator candidate which can potentially exhibit axion electrodynamics. We observe a unique magnetic field-driven phase diagram where the second-order antiferromagnetic to paramagnetic phase boundary bifurcates into two first-order lines at the tricritical point. The two first-order lines enclosing the metamagnetic phase eventually terminate at the quantum critical endpoints with the application of magnetic field.