Direct Dark Matter searches with Metal Halide Perovskites

TL;DR

This work targets direct detection of sub-MeV dark matter via single-phonon excitations in polar materials, proposing metal halide perovskites (MAPbI3, MAPbBr3, CsPbI3) as promising targets and identifying CsPbI3 as the leading option due to its low optical-phonon gaps and anisotropy that enables daily modulation. The authors develop a dark photon-mediated scattering framework tied to the dielectric energy-loss function $\mathcal{L}(\omega,0)$ and support the analysis with ab initio DFT calculations to pinpoint dominant phonon modes and characterize crystal anisotropy effects. They report that CsPbI3 offers the strongest projected exclusion for DM scattering down to $m_{\chi} \sim \text{keV}$ and improves dark-photon absorption sensitivity below $\sim10\,\text{meV}$, with daily modulation providing a distinctive handle on the signal. Finally, they outline a feasible experimental path using kilogram-scale CsPbI3 crystals and superconducting kinetic-inductance detectors at millikelvin temperatures, underscoring the practical potential to probe new regions of light dark matter parameter space.

Abstract

Polar materials with optical phonons in the meV range are excellent candidates for both dark matter direct detection (via dark photon-mediated scattering) and light dark matter absorption. In this study, we propose, for the first time, the metal halide perovskites MAPbI$_3$, MAPbCl$_3$, and CsPbI$_3$ for these purposes. Our findings reveal that CsPbI$_3$ is the best material, significantly improving exclusion limits compared to other polar materials. For scattering, CsPbI$_3$ can probe dark matter masses down to the keV range. For absorption, it enhances sensitivity to detect dark photon masses below $\sim 10~{\rm meV}$. The only material which has so far been investigated and that could provide competitive bounds is CsI, which, however, is challenging to grow in kilogram-scale sizes due to its considerably lower stability compared to CsPbI$_3$. Moreover, CsI is isotropic while the anisotropic structure of CsPbI$_3$ enables daily modulation analysis, showing that a significant percentage of daily modulation exceeding 1% is achievable for dark matter masses below $40~{\rm keV}$.

Figures (7)

• Figure 1: Reference DM-electron cross section as a function of $m_\chi$. The sensitivity is computed for a kg-year exposure on CsPbI$_3$, MAPbI$_3$, MAPbBr$_3$ (solid lines) compared with other materials already analyzed in literature (dashed lines). We plot the cross sections needed to obtain 3 events for a kg-year exposure corresponding to a 95% confidence level exclusion limit assuming a zero background. We used the parameters reported in Table \ref{['tab:omegas']} within the narrow width approximation. The light gray shadow region indicates stellar constraints Stellar1.
• Figure 2: Top panel: Crystal structure of $\gamma$-CsPbI$_3$ with lattice parameters, shown from both top and lateral views. Bottom panel: Phonon dispersion on the $\Gamma$-X-R-$\Gamma$-Z high symmetry path (left) and PDOS (right).
• Figure 3: Top panel:$\Bar{\sigma}_e$ as a function of $m_\chi$ as in Fig. \ref{['fig:sigma']}. Black solid line shows the total rate obtained through DFT, while with different colors denote the contribution of five modes. Dashed red curves the rate obtained summing these five modes. Bottom panel: (Left) Rate contribution for three different $m_{\chi}$ masses, projected onto the phonon dispersion along the $\Gamma$-X-R-$\Gamma$-Z high symmetry path. (Right) Total rate Density of States for three different $m_{\chi}$ masses (1, 5 and 40 keV). In the left panel, the point sizes are proportional to the normalized rate for each mass, considering only the contributions along the specified high-symmetry path. In the right panel, the differential rate $1/R\, dR/d\omega|_{m_\chi}$ represents the normalized rate contributions across the entire Brillouin zone for each mass.
• Figure 4: Left panel: The maximal daily modulation amplitude, $f_{\rm mod}$, as a function of $m_\chi$, as defined in Eq. \ref{['eq:fmod']}, is shown for CsPbI$_3$—with the green and orange solid lines representing the $\gamma$ and $\delta$ phases, respectively. The black solid line corresponds to the results for Al$_2$O$_3$ as computed in ZurekPRD2018TargCompSinglph. The red shaded area indicates the region where $f_{\rm mod} < 1\%$, highlighting that the statistical significance is too low to robustly confirm the modulating nature of the DM signal. Right panel: The cross-section $\Bar{\sigma}_e$ as a function of DM mass for $\gamma$-CsPbI$_3$ (solid green), $\delta$-CsPbI$_3$ (solid orange) and Al$_2$O$_3$ (solid black), calculated using DFT. The dashed lines represent the 95% CL exclusion limits assuming zero observed events and no background. The $\pm1\sigma$ bands indicate the modulation reach for DM masses with $f_{\rm mod} > 0.01$, where the non-modulating hypothesis can be rejected and the statistical significance of a non-modulating signal can be established. Moreover the gray shaded region represents the stellar constraints as in Fig. \ref{['fig:sigma']}.
• Figure 5: Exclusion limit at 95% CL cross section reach with kg-yr exposure and zero background. The exclusion limits are computed using DarkELFDarkELF, in terms of the kinetic mixing parameter $\kappa$ for kg-year exposure (single phonon excitation). The width of the dips depends on both the parameter $\gamma$ and the temperature at which the ELF experimental data were collected.