Absorption of light dark matter in semiconductors

TL;DR

This paper explores how semiconductors can detect very light dark matter through absorption processes, extending detection capabilities below the band gap and using existing and future experiments to probe new parameter spaces.

Contribution

It introduces the concept of dark matter absorption in semiconductors for masses below the band gap, expanding detection methods for sub-eV dark matter particles.

Findings

Semiconductors can detect dark matter via absorption below the band gap.

Existing experiments already constrain new parameter space for light dark matter.

Low-threshold semiconductor detectors can surpass current astrophysical constraints.

Abstract

Semiconductors are by now well-established targets for direct detection of MeV to GeV dark matter via scattering off electrons. We show that semiconductor targets can also detect significantly lighter dark matter via an absorption process. When the dark matter mass is above the band gap of the semiconductor (around an eV), absorption proceeds by excitation of an electron into the conduction band. Below the band gap, multi-phonon excitations enable absorption of dark matter in the 0.01 eV to eV mass range. Energetic dark matter particles emitted from the sun can also be probed for masses below an eV. We derive the reach for absorption of a relic kinetically mixed dark photon or pseudoscalar in germanium and silicon, and show that existing direct detection results already probe new parameter space. With only a moderate exposure, low-threshold semiconductor target experiments can exceed current astrophysical and terrestrial constraints on sub-keV bosonic dark matter.