Revisiting the Dark Matter Interpretation of Excess Rates in
  Semiconductors
  In light of recent results from low-threshold dark matter detectors, we
revisit the possibility of a common dark matter origin for multiple excesses
across numerous direct detection experiments, with a focus on the excess rates
in semiconductor detectors. We explore the interpretation of the low-threshold
calorimetric excess rates above 40 eV in the silicon SuperCDMS Cryogenic Phonon
Detector and above 100 eV in the germanium EDELWEISS Surface detector as
arising from a common but unknown origin, and demonstrate a compatible fit for
the observed energy spectra in both experiments, which follow a power law of
index $\alpha = 3.43^{+0.11}_{-0.06}$. Despite the intriguing scaling of the
normalization of these two excess rates with approximately the square of the
mass number $A^2$, we argue that the possibility of common origin by dark
matter scattering via nuclear recoils is strongly disfavored, even allowing for
exotic condensed matter effects in an as-yet unmeasured kinematic regime. We
also investigate the possibility of inelastic nuclear scattering by cosmic ray
neutrons, solar neutrinos, and photons as the origin, and quantitatively
disfavor all three based on known fluxes of particles.
