Multiphonon excitations from dark matter scattering in crystals

TL;DR

This paper analytically calculates the rate at which light dark matter particles can produce multiphonon excitations in cubic crystals, highlighting conditions where multiphonon processes may dominate over single phonon events for detection.

Contribution

It provides the first analytic calculation of multiphonon excitation rates from sub-MeV dark matter scattering in cubic crystals, identifying scenarios where these processes are most promising.

Findings

Multiphonon rates are smaller than single optical phonon rates when accessible.

In Si and diamond, multiphonon production can surpass single phonon detection depending on thresholds.

Analytic expressions enable better understanding of dark matter detection via phonon excitations.

Abstract

For direct detection of sub-MeV dark matter, a promising strategy is to search for individual phonon excitations in a crystal. We perform an analytic calculation of the rate for light dark matter (keV $<m_{DM}<$ MeV) to produce two acoustic phonons through scattering in cubic crystals such as GaAs, Ge, Si and diamond. The multiphonon rate is always smaller than the rate to produce a single optical phonon, whenever the latter is kinematically accessible. In Si and diamond there is a dark matter mass range for which multiphonon production can be the most promising process, depending on the experimental threshold.