Towards Quantum-Dot Detectors as Barcodes for Dark Matter Interactions

Identifying the nature of sub-GeV dark matter requires detecting inelastic scattering processes with target electrons, but standard bulk semiconductor targets lack the tunability needed to distinguish between different theoretical interaction models. This paper presents the first ab initio calculation of dark matter scattering on electrons bound in silicon quantum dots. By examining how quantum confinement and surface passivation alter electronic responses, the authors evaluate whether arrays of quantum dots with varying morphologies can serve as distinguishing barcodes for dark matter interactions.

Using density functional theory calculations within the Quantum ESPRESSO and QEdark-EFT frameworks, the authors model silicon quantum dots of different sizes and surface terminations, specifically hydrogen-terminated and alkyl-terminated systems. They compute the momentum-dependent electronic responses and optical gaps for these nanocrystals. To test their diagnostic power, they propose a detector concept consisting of independent target subunits loaded with silicon quantum dots of specific morphologies, read out by Skipper charge-coupled devices to measure single-photon scintillation signals.

While the per-mass interaction rate in quantum dots is suppressed by a factor of a few compared to bulk silicon, the surface-only readout allows the detector background to scale with area rather than mass. More importantly, because the electronic gap and form factors depend strongly on nanocrystal diameter and surface ligands, different dark matter models yield unique relative rates across an array of distinct quantum dot targets. This barcode pattern provides a powerful capability to discriminate between interaction operators and mediator types given a future dark matter signal.