We present the first Ge-based constraints on sub-$\mathrm{MeV}/c^2$ dark matter (DM) particles interacting with electrons using a 33.4 g Ge cryogenic detector with a 0.53 electron-hole pair (rms) resolution, operated underground at the Laboratoire Souterrain de Modane. Competitive constraints are set on the DM-electron scattering cross section, as well as on the kinetic mixing parameter of dark photons down to $1\mathrm{eV}/c^2$. In particular, the most stringent limits are set for dark photon DM in the 6 to $9\mathrm{eV}/c^2$ range. These results demonstrate the high relevance of Ge cryogenic detectors for the search of DM-induced eV-scale electron signals.

• Received 24 March 2020
• Revised 7 July 2020
• Accepted 31 August 2020

DOI:https://doi.org/10.1103/PhysRevLett.125.141301