Spectral and optical properties of Ag3Au(Se2,Te2) and dark matter detection

Abstract

In this work we study the electronic structure of Ag3AuSe2 and Ag3AuTe2, two chiral insulators whose gap can be tuned through small changes in the lattice parameter by applying hydrostatic pressure or choosing different growth protocols. Based on first principles calculations we compute their band structure for different values of the lattice parameters and show that while Ag3AuSe2 retains its direct narrow gap at the Γ point, Ag3AuTe2 can turn into a metal. Focusing on Ag3AuSe2 we derive a low energy model around Γ using group theory, which we use to calculate the optical conductivity for different values of the lattice constant. We discuss our results in the context of detection of light dark matter particles, which have masses of the order of a keV, and conclude that Ag3AuSe2 satisfies three important requirements for a suitable detector: small Fermi velocities, meV band gap, and low photon screening. Our work motivates the growth of high-quality and large samples of Ag3AuSe2 to be used as target materials in dark matter detectors.