Dark Matter Direct Detection in Materials with Spin-Orbit Coupling

TL;DR

This paper investigates how spin-orbit coupling in narrow-gap semiconductors affects dark matter detection rates, using advanced density functional theory to improve the accuracy of scattering and absorption predictions.

Contribution

It introduces a formalism incorporating spin-orbit coupling effects into dark matter-electron interaction calculations in materials with narrow band gaps.

Findings

SOC significantly alters projected dark matter constraints.

Application to ZrTe$_{5}$ demonstrates the importance of including SOC.

Enhanced theoretical framework for future dark matter detection studies.

Abstract

Semiconductors with $\mathcal{O}(\text{meV})$ band gaps have been shown to be promising targets to search for sub-MeV mass dark matter (DM). In this paper we focus on a class of materials where such narrow band gaps arise naturally as a consequence of spin-orbit coupling (SOC). Specifically, we are interested in computing DM-electron scattering and absorption rates in these materials using state-of-the-art density functional theory (DFT) techniques. To do this, we extend the DM interaction rate calculation to include SOC effects which necessitates a generalization to spin-dependent wave functions. We apply our new formalism to calculate limits for several DM benchmark models using an example ZrTe$_{5}$ target and show that the inclusion of SOC can substantially alter projected constraints.