Detecting Superlight Dark Matter with Fermi-Degenerate Materials

TL;DR

This paper proposes using superconducting Fermi-degenerate materials with transition edge sensors to detect ultra-light dark matter particles down to keV masses, leveraging their sensitivity to small energy deposits and compatibility with cosmological constraints.

Contribution

It introduces a concrete experimental setup employing superconductors for detecting light dark matter, analyzing constraints, and exploring material effects on detection sensitivity.

Findings

Superconductors can detect dark matter with masses below 1 MeV.

Metal targets experience suppression for certain mediators, while insulators do not.

Models consistent with cosmological constraints are observable with proposed detectors.

Abstract

We examine in greater detail the recent proposal of using superconductors for detecting dark matter as light as the warm dark matter limit of O(keV). Detection of such light dark matter is possible if the entire kinetic energy of the dark matter is extracted in the scattering, and if the experiment is sensitive to O(meV) energy depositions. This is the case for Fermi-degenerate materials in which the Fermi velocity exceeds the dark matter velocity dispersion in the Milky Way of ~10^-3. We focus on a concrete experimental proposal using a superconducting target with a transition edge sensor in order to detect the small energy deposits from the dark matter scatterings. Considering a wide variety of constraints, from dark matter self-interactions to the cosmic microwave background, we show that models consistent with cosmological/astrophysical and terrestrial constraints are observable with such detectors. A wider range of viable models with dark matter mass below an MeV is available if dark matter or mediator properties (such as couplings or masses) differ at BBN epoch or in stellar interiors from those in superconductors. We also show that metal targets pay a strong in-medium suppression for kinetically mixed mediators; this suppression is alleviated with insulating targets.