Magnetic torque oscillations from warped helical surface states in topological insulators

TL;DR

This paper introduces a magnetic torque method to detect warping and mass gaps in the surface states of topological insulators, providing a new experimental signature for their properties.

Contribution

The paper proposes a novel magnetic torque technique to probe surface state warping and mass gaps in topological insulators, linking torque oscillations to surface state characteristics.

Findings

Torque oscillations depend on surface state warping and mass gap.

The method reveals symmetry reduction in torque oscillations due to the mass gap.

Torque varies with field strength, angle, and chemical potential.

Abstract

A magnetic torque method is proposed that probes the warping and mass gap of Dirac cone surface states in topological insulators like Bi2X3 (X=Se,Te). A rotating field parallel to the surface induces a paramagnetic moment in the helical surface states for nonzero warping. It is non-collinear with the applied field and therefore produces torque oscillations as function of the field angle which are a direct signature of the surface states. The torque dependence on field strength and angle, the chemical potential and the Dirac cone parameters like warping strength and mass gap is calculated. It is shown that the latter leads to a symmetry reduction in the fourfold torque oscillations.