Crossover between weak localization and weak antilocalization in magnetically doped topological insulator

TL;DR

This study investigates how magnetic doping in topological insulators causes a crossover from weak antilocalization to weak localization, revealing complex transport phenomena linked to Berry phase evolution and magnetic impurities.

Contribution

It provides experimental evidence of WAL to WL crossover in magnetically doped TIs and explains the phenomena through Berry phase and energy gap considerations.

Findings

Crossover from WAL to WL with increased Cr doping

WAL reenters at higher temperatures despite heavy doping

Magnetic field can revert WL back to WAL

Abstract

Topological insulators (TI) are a new class of quantum materials with insulating bulk enclosed by topologically protected metallic boundaries. The surface states of three-dimensional TIs have spin helical Dirac structure, and are robust against time reversal invariant perturbations. This extraordinary property is notably exemplified by the absence of backscattering by nonmagnetic impurities and the weak antilocalization (WAL) of Dirac fermions. Breaking the time reversal symmetry (TRS) by magnetic element doping is predicted to create a variety of exotic topological magnetoelectric effects. Here we report transport studies on magnetically doped TI Cr-Bi2Se3. With increasing Cr concentration, the low temperature electrical conduction exhibits a characteristic crossover from WAL to weak localization (WL). In the heavily doped regime where WL dominates at the ground state, WAL reenters as temperature rises, but can be driven back to WL by strong magnetic field. These complex phenomena can be explained by a unified picture involving the evolution of Berry phase with the energy gap opened by magnetic impurities. This work demonstrates an effective way to manipulate the topological transport properties of the TI surface states by TRS-breaking perturbations.