Abstract
We propose the use of three-dimensional Dirac materials as targets for direct detection of sub-MeV dark matter. Dirac materials are characterized by a linear dispersion for low-energy electronic excitations, with a small band gap of O(meV) if lattice symmetries are broken. Dark matter at the keV scale carrying kinetic energy as small as a few meV can scatter and excite an electron across the gap. Alternatively, bosonic dark matter as light as a few meV can be absorbed by the electrons in the target. We develop the formalism for dark matter scattering and absorption in Dirac materials and calculate the experimental reach of these target materials. We find that Dirac materials can play a crucial role in detecting dark matter in the keV to MeV mass range that scatters with electrons via a kinetically mixed dark photon, as the dark photon does not develop an in-medium effective mass. The same target materials provide excellent sensitivity to absorption of light bosonic dark matter in the meV to hundreds of meV mass range, superior to all other existing proposals when the dark matter is a kinetically mixed dark photon.
Highlights
The search for sub-GeV dark matter (DM) is a growing frontier in direct detection experiments
The light kinetically mixed mediator scenario we have considered here is interesting for direct detection with Dirac materials because the scattering rate is greatly enhanced at low momentum transfer due to the 1=q4 dependence of the DM form factor jFDMj2
We have shown that 3D Dirac materials are excellent targets to use in searches for sub-MeV DM
Summary
The search for sub-GeV dark matter (DM) is a growing frontier in direct detection experiments. Allowing the two Weyl fermions to couple, for example by applying strain to a Dirac semimetal or tuning a topological insulator close to the semimetal critical point [68], can lead to a finite Δ ≠ 0 that is typically small, 2Δ ∼ meV Such a gap can suppress thermal interband transitions, which is crucial for making detection of meV-scale DM-induced excitations feasible.. III and IV to calculate the DM scattering rate mediated by a dark photon and the dark photon absorption rate in Dirac materials, 3In Weyl semimetals, the two Weyl fermions are generically located at different points in momentum space and are decoupled at low energies [69,70,71,72], making it difficult to open a gap. The four appendixes describe the derivation of the transition form factor for a generic Dirac material, the generalization of the scattering rate to anisotropic semimetals, the scattering and absorption reach for models other than the light kinetically mixed dark photon, and the density functional theory (DFT) calculations used to derive the band structure of ZrTe5
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