Dirac materials for sub-MeV dark matter detection: New targets and improved formalism

Abstract

Because of their tiny band gaps Dirac materials promise to improve the sensitivity for dark matter particles in the sub-MeV mass range by many orders of magnitude. Here we study several candidate materials and calculate the expected rates for dark matter scattering via light and heavy dark photons as well as for dark photon absorption. A particular emphasis is placed on how to distinguish a dark matter signal from background by searching for the characteristic daily modulation of the signal, which arises from the directional sensitivity of anisotropic materials in combination with the rotation of the Earth. We revisit and improve previous calculations and propose two new candidate Dirac materials: BNQ-TTF and Yb 3 PbO. We perform detailed calculations of the band structures of these materials and of ZrTe 5 based on density functional theory and determine the band gap, the Fermi velocities and the dielectric tensor. We show that in both ZrTe 5 and BNQ-TTF the amplitude of the daily modulation can be larger than 10% of the total rate, allowing to probe the preferred regions of parameter space even in the presence of sizeable backgrounds. BNQ-TTF is found to be particularly sensitive to small dark matter masses (below 100 keV for scattering and below 50 meV for absorption), while Yb 3 PbO performs best for heavier particles.

Dark matter interpretation of excesses in multiple direct detection experiments

“…(3) In an anisotropic material where plasmon-phonon interactions or the dielectric function are directional, a daily modulation may be seen. In the direct excitation model, there may also be strong directional signals in low-threshold experiments searching for the dominant 1 − f cold DM fraction [46,[100][101][102][103]. (4) The secondary plasmon hypothesis from Sec.…”

Impact of uncertainties in the halo velocity profile on direct detection of sub-GeV dark matter

“…E.g. for F (q) ∝ 1/q 2 the sensitivity difference is O (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30). Moreover, for lower DM masses the effect is much larger, due to higher sensitivity of the tail of the velocity distribution.…”

“…More recently a lot of effort has been dedicated to developing novel detection techniques applicable to sub-GeV DM. These include, but are not limited to electron JHEP07(2020)081 transitions: in atoms and semiconductors [9][10][11][12][13][14][15][16][17], superconductors [18][19][20], topological insulators [21,22] and Dirac materials [23][24][25]. Sub-GeV DM can be searched for also via the Migdal effect [26][27][28][29], single phonon [30,31] and magnon [32] excitations in crystals, in superfluid helium [33,34], through dissociation or excitation in molecules [35,36] and also through other methods [37][38][39][40][41][42] proposed recently.…”

Plasmon production from dark matter scattering

“…The corresponding energy loss, W T , is given by the transverse contributions to Eq. (12). Noting that the number of photons produced at a given energy is dW T =ω, the photon production rate is…”

“…As experiments lower their energy thresholds, collective many-body effects can become increasingly important and enhance the discovery potential beyond that of traditional searches for hard nuclear recoils. Examples can be found in numerous theoretical studies of direct detection of sub-GeV dark matter, including with semiconductors [2][3][4][5], superconductors [6][7][8], Dirac materials [9][10][11][12][13], phonon excitations in crystals [14][15][16][17], phonons in superfluid He [18][19][20], and others.…”