Defect Creation in Crystals: A Portal to Directional Dark Matter Searches

A large body of astrophysical observations indicate that around 85% of the matter in the universe is not made of recognized standard model particles. Understanding the nature of this so-called dark matter is of fundamental importance to cosmology, astrophysics, and high-energy particle physics. We examine the response of commonly used semiconductor materials to low-mass WIMP interactions using numerical simulations based on classical interatomic potentials in these materials. These simulations, backed up by more precise density functional theory simulations and experiments, predict a nonlinear energy loss that never produces phonons due to the nonzero energy required to form crystallographic defects. We argue that such nonlinear effects related to defect formation in electron-volt-scale resolution semiconductor detectors allows for very effective directional sensitivity and possible statistical nuclear recoil discrimination to dark matter signals for masses below 1 GeV / c².