Directly Detecting Sub-GeV Dark Matter with Electrons from Nuclear Scattering

Dark matter (DM) particles with mass in the sub-GeV range are an attractive alternative to heavier weakly interacting massive particles, but direct detection of such light particles is challenging. If, however, DM-nucleus scattering leads to ionization of the recoiling atom, the resulting electron may be detected even if the nuclear recoil is unobservable. We demonstrate that including this effect significantly enhances direct detection sensitivity to sub-GeV DM. Existing experiments set world-leading limits, and future experiments may probe the cross sections relevant for thermal freeze-out.