Magnetoresistance from time-reversal symmetry breaking in topological materials

TL;DR

This paper investigates how magnetic fields influence topological materials' electronic properties, revealing that Zeeman effects induce measurable magnetoresistance, especially near the Dirac point, due to spin alignment and Fermi velocity changes.

Contribution

It re-evaluates the Drude model for topological materials, highlighting Zeeman-dependent factors and demonstrating magnetoresistance effects in 2D Dirac states on topological insulator surfaces.

Findings

Magnetoresistance is significant in 2D Dirac states of topological insulators.

Magnetoresistance depends strongly on spin-orbit energy and Fermi level position.

Zeeman effects alter scattering time and Fermi velocity, affecting conductivity.

Abstract

Magnetotransport measurements are a popular way of characterizing the electronic structure of topological materials and often the resulting datasets cannot be described by the well-known Drude model due to large, non-parabolic contributions. In this work, we focus on the effects of magnetic fields on topological materials through a Zeeman term included in the model Hamiltonian. To this end, we re-evaluate the simplifications made in the derivations of the Drude model and pinpoint the scattering time and Fermi velocity as Zeeman-term dependent factors in the conductivity tensor. The driving mechanisms here are the aligment of spins along the magnetic field direction, which allows for backscattering, and a significant change to the Fermi velocity by the opening of a hybridization gap. After considering 2D and 3D Dirac states, as well as 2D Rashba surface states and the quasi-2D bulk states of 3D topological insulators, we find that the 2D Dirac states on the surfaces of 3D topological insulators produce magnetoresistance, that is significant enough to be noticable in experiments. As this magnetoresistance effect is strongly dependent on the spin-orbit energy, it can be used as a telltale sign of a Fermi energy located close to the Dirac point.