Dilute magnetic topological semiconductors: What's new beyond the physics of dilute magnetic semiconductors?

TL;DR

This paper explores the emergence of a novel disordered metallic state in dilute magnetic topological semiconductors, characterized by inhomogeneous Weyl metallic islands within insulating phases, driven by disorder and spin-orbit coupling.

Contribution

It introduces the concept of dilute magnetic topological semiconductors and proposes a phase diagram with a new insulator-metal transition involving inhomogeneous Weyl metallic states.

Findings

Identification of a disordered metallic state with Weyl islands

Phase diagram linking spin-orbit coupling, disorder, and temperature

Proposal of experimental verification via atomic force microscopy

Abstract

Role of localized magnetic moments in metal-insulator transitions lies at the heart of modern condensed matter physics, for example, the mechanism of high T$_{c}$ superconductivity, the nature of non-Fermi liquid physics near heavy fermion quantum criticality, the problem of metal-insulator transitions in doped semiconductors, and etc. Dilute magnetic semiconductors have been studied for more than twenty years, achieving spin polarized electric currents in spite of low Curie temperatures. Replacing semiconductors with topological insulators, we propose the problem of dilute magnetic topological semiconductors. Increasing disorder strength which corresponds to the size distribution of ferromagnetic clusters, we suggest a novel disordered metallic state, where Weyl metallic islands appear to form inhomogeneous mixtures with topological insulating phases. Performing the renormalization group analysis combined with experimental results, we propose a phase diagram in $(\lambda_{so},\Gamma,T)$, where the spin-orbit coupling $\lambda_{so}$ controls a topological phase transition from a topological semiconductor to a semiconductor with temperature $T$ and the distribution for ferromagnetic clusters $\Gamma$ gives rise to a novel insulator-metal transition from either a topological insulating or band insulating phase to an inhomogeneously distributed Weyl metallic state with such insulating islands. Since electromagnetic properties in Weyl metal are described by axion electrodynamics, the role of random axion electrodynamics in transport phenomena casts an interesting problem beyond the physics of percolation in conventional disorder-driven metal-insulator transitions. We also discuss how to verify such inhomogeneous mixtures based on atomic force microscopy.