  We propose to use high-purity lab-grown diamond for the detection of sub-GeV
dark matter. Diamond targets can be sensitive to both nuclear and electron
recoils from dark matter scattering in the MeV and above mass range, as well as
to absorption processes of dark matter with masses between sub-eV to 10's of
eV. Compared to other proposed semiconducting targets such as germanium and
silicon, diamond detectors can probe lower dark matter masses via nuclear
recoils due to the lightness of the carbon nucleus. The expected reach for
electron recoils is comparable to that of germanium and silicon, with the
advantage that dark counts are expected to be under better control. Via
absorption processes, unconstrained QCD axion parameter space can be
successfully probed in diamond for masses of order 10 eV, further demonstrating
the power of our approach.
