Detection of topological states in two-dimensional Dirac systems by the dynamic spin susceptibility

TL;DR

This paper demonstrates that dynamic spin susceptibility measurements can directly identify topological phases in 2D Dirac systems through characteristic resonance features, providing a bulk property-based method for topological insulator characterization.

Contribution

It introduces a novel approach using dynamic spin susceptibility to distinguish topological from trivial phases in 2D Dirac systems without needing to observe topological transitions.

Findings

Resonant peak in DSS indicates topological state under static magnetic field.

Threshold frequency in DSS differentiates topological and trivial phases.

DSS line shapes vary with topological phase, enabling phase identification.

Abstract

We discuss dynamic spin susceptibility (DSS) in two-dimensional (2D) Dirac electrons with spin-orbit interactions to characterize topological insulators. The imaginary part of the DSS appears as an absorption rate in response to a transverse ac magnetic field, just as in an electron spin resonance experiment for localized spin systems. We found that when the system is in a static magnetic field, the topological state can be identified by an anomalous resonant peak of the imaginary part of the DSS as a function of the frequency of the transverse magnetic field $\omega$. In the absence of a static magnetic field, the imaginary part of the DSS becomes a continuous function of $\omega$ with a threshold frequency $\omega_{\rm c}$. In this case, the topological and the trivial phases can also be distinguished by the values of $\omega_{\rm c}$ and by the line shapes. Thus the DSS is an experimentally observable physical quantity to characterize a topological insulator directly from bulk properties, without observing a topological transition.