Speaker
Description
We test the influence of the detailed description of the electronic structure in crystalline silicon and germanium on the resulting calculated response of the electrons to general dark matter interactions.
We show that if the dark matter interaction energy reaches a threshold of about 30 eV, electron excitations from tightly-bound germanium 3$d$ states become important and since these are very narrow, they suffer from incorrect electron self-interaction in the local density approximation to density functional theory. We address this problem by introducing a Hubbard U-correction term that corrects the energy of these bands and restores them to the experimentally observed value. We then calculate the scattering rates coming from general crystal responses and put constraints on current experiments that are using silicon and germanium targets.
