Direct Detection of sub-GeV Dark Matter with Semiconductor Targets


Rouven Essig, Marivi Fernandez-Serra, Jeremy Mardon, Adrian Soto, Tomer Volansky, Tien-Tien Yu

Basic Idea

Dark matter in the sub-GeV mass range is a theoretically motivated but largely unexplored paradigm. Such light masses are out of reach for conventional nuclear recoil direct detection experiments, but may be detected through the small ionization signals caused by dark matter-electron scattering. Semiconductors are well-studied and are particularly promising target materials because their O(1 eV) band gaps allow for ionization signals from dark matter as light as a few hundred keV. Current direct detection technologies are being adapted for dark matter-electron scattering. We provide the theoretical calculations for dark matter-electron scattering rate in semiconductors, overcoming several complications that stem from the many-body nature of the problem. We use density functional theory to numerically calculate the rates for dark matter-electron scattering in silicon and germanium, and estimate the sensitivity for upcoming experiments such as DAMIC and SuperCDMS. The results on this page can be used by experimental collaborations to calculate their own sensitivities based on their specific setup.

Input Data

The github repository for QEdark can be found here. To run QEdark yourself, you will need the following files (use right-click and "Save As" to download the files):

Input files: ge.243.in, si.243.in
Pseudopotentials: Ge.pbe-dn-rrkjus_psl.0.2.2.UPF, Si.pbe-n-rrkjus_psl.0.1.UPF
Dark Matter parameters: dm.Si.dat, dm.Ge.dat


The following is the output of QEdark for the form factor integrated over a Maxwell-Boltzmann distribution with v0=230 km/s, vesc=600 km/s, vearth=240km/s, and delta v=15 km/s. Included is a Mathematica notebook which analyzes the data and plots the cross-section reach vs. dark matter mass for Q=1-12, the recoil spectra, and the modulation rate.

Integrated form factors: Germanium Semicore Only, Germanium Valence Only, Silicon
Analysis notebook: QEdark.nb

The following is the unintegrated form factor. The user will need to specify a dark matter velocity profile to calculate the expected rates.

Unintegrated form factors: Silicon, Germanium
Analysis notebook: QEdark_f2.nb
Contact: Tien-Tien Yu