Topological phase control in Mn1-xGexBi2Te4 via spin-orbit coupling and magnetic configuration engineering

TL;DR

This study uses density functional theory to explore how spin-orbit coupling, strain, and chemical substitution can induce and control topological phase transitions, including Weyl semimetal phases, in Mn1-xGexBi2Te4 compounds with magnetic order.

Contribution

It reveals mechanisms for topological phase control via SOC, strain, and local chemical asymmetry, and proposes methods to optimize Weyl points and anomalous Hall effect in magnetic topological materials.

Findings

Weyl semimetal phase requires crossing of bands with opposite spin projections.

SOC and strain modulation can induce topological phase transitions.

Local Ge substitution can induce Weyl states in antiferromagnetic systems.

Abstract

Magnetic topological systems based on MnBi2Te4 have recently attracted significant attention due to their rich interplay between magnetism and topological electronic states. In this work, using density functional theory (DFT), we investigate topological phase transitions (TPTs) in Mn1-xGexBi2Te4 compounds with both ferromagnetic (FM) and antiferromagnetic (AFM) ordering under variations of spin-orbit coupling (SOC) strength and uniaxial strain along the c axis. We show that the emergence of a Weyl semimetal (WSM) phase requires the crossing of bands with opposite sz spin projections along the {\Gamma}Z direction. Modulation of SOC and strain can annihilate Weyl points via spin-selective hybridization, driving transitions into trivial or topological insulating phases. Furthermore, we demonstrate that local asymmetry in Mn/Ge substitution, particularly at 37.5% Ge concentration (Mn0.625Ge0.375Bi2Te4) can locally disrupt AFM interlayer coupling and induce a WSM state even in globally AFM systems, without external remagnetization. To optimize Weyl point separation and enhance the anomalous Hall effect (AHE), we propose partial substitution of Mn by Fe and Te by Se.