Chiral phonons in metal-organic frameworks as quantum sensors for the direct detection of dark matter

TL;DR

The paper tackles the challenge of direct dark matter detection at sub-eV energy scales by proposing a chiral phonon-based quantum sensor built from noncentrosymmetric MOFs. It develops a DM–phonon interaction framework within an effective field theory, evaluating both heavy- and light-m mediator scenarios across multiple EFT operators, and couples this to ab initio calculations of phonon chirality to predict detector performance. Ab initio results reveal MOFs host flat, low-energy acoustic bands with sizable chiral phonon content, enabling a detectable magnetic signal characterized by a chirality factor κ ≈ 0.16 and robust sensitivity across MOFs, unlike some inorganic crystals. The work proposes a practical prototype with an surface-based magnetometer (asymmetric SQUID) to read out single chiral phonons, and discusses background mitigation via directional and veto strategies. Altogether, this approach offers a path toward tabletop, sub-eV DM detectors and expands the toolbox of phonon-based quantum sensors for fundamental physics.

Abstract

We investigate a new quantum sensor for dark matter direct detection with sub-eV sensitivity, focusing on several candidate materials that potentially host chiral phonons with large magnetic moments that can be directly read out with an external magnetometer. We focus on metal-organic frameworks (MOFs) as possible candidate materials for single chiral phonon detection due to their noncentrosymmetric structure, tunability, and the ability to host these excitations in stable acoustic bands. We identify several promising candidates and compare their projected dark matter detection sensitivity for all possible interactions identified within effective field theory. We establish that the expected sensitivity does not depend heavily on the specific choice of the MOF, enabling us to tailor the final material composition to facilitate the magnetic readout. We then propose a prototype setup able to test the direct readout of a chiral phonon sensor with a surface-integrated magnetometer.

Figures (16)

• Figure 1: Crystal structures of noncentrosymmetric materials studied as candidate chiral phonon DM detector targets: GaAs (space group $F\overline{4}3m$), LiNbO$_3$ ($R3c$), Li$_2$(tartrate) (Li$_2$(tar), $P2_1$), Sr(tartrate) (Sr(tar), $C222_1$), InF$_3$(bipyridine) (InF$_3$(bpy), $I222$), AgCl(phenanthroline) (AgCl(phen), $C2$), Zn(NH$_4$)(formate)$_3$, (Zn(NH$_4$)(formate)$_3$, $P6_3$) Cd(guanadinium)(formate)$_3$ (Cd(Gua)(fmt)$_3$, $Cc$), and CuCl(pyrimidine) (CuCl(pyr), $Pma2$). H atoms are shown in pink, Li atoms in pale green, C atoms in brown, N atoms in lilac, O atoms in red, F atoms in cyan, Cl atoms in bright green, Cu atoms in blue, Zn atoms in dark grey, Ga atoms in blue-green, As atoms in violet, Sr atoms in dark green, Nb atoms in yellow, Ag atoms in light grey, Cd atoms in purple, and In atoms in magenta. Unit cell vectors are marked as black lines.
• Figure 2: Calculated phonon band structures of GaAs (panel a), LiNbO$_3$ (panel b), CuCl(pyr) (panel c), and AgCl(phen) (panel d), with bands coloured according to their phonon chirality, as quantified by the magnitude of the phonon angular momentum ($||\mathbf{J}||$). Special points in and paths through the Brillouin zone were chosen following the literature hinuma2017band. The dynamical matrices of GaAs and LiNbO$_3$ were obtained from the literature osti_1200591uedaChiral2025.
• Figure 3: Phonon angular momentum ($\mathbf{J}$) in the lowest-energy acoustic band of GaAs (panel a), LiNbO$_3$ (panel b), and CuCl(pyr) (panel c). Phonon modes in this band are displayed as points on a $10 \times 10 \times 10$ grid in reciprocal space, with the colour of the point showing the magnitude of $\mathbf{J}$ and the size of the point displayed in proportion to the phonon energy. The expectation value of the phonon angular momentum in this band ($\langle ||\mathbf{J}_1|| \rangle$) is used to estimate $\kappa$, the probability of the decay of an excitation into at least one detectable chiral phonon. For GaAs, $\kappa = 0.07$, for LiNbO$_3$$\kappa = 0.22$, for CuCl(pyr) $\kappa = 0.16$. Unstable modes in CuCl(pyr) are not shown.
• Figure 4: Testing setup for a chiral phonon sensor prototype. A material which hosts magnetic chiral phonons is mounted with a surface magnetometer (in our example, an assymmetric SQUID in a 4-probe setup). Chiral phonons are excited by a circularly polarized laser pulse and the magnetic field fluctuation they generate is read out with the magnetometer (panel a). Upon switching polarization of the laser, the magnetic field induced by chiral phonons is inverted (panel b). An unpolarized laser pulse induces identical populations of phonons of both chiralities, resulting in a suppressed magnetic response of the sample for benchmarking purposes (panel c). A population of chiral phonons with a preferred handedness can also be excited by application of a thermal gradient driving a preferential direction of phononic transport (panel d).
• Figure 5: The dark photon interaction sensitivity for various MOF targets with kg$\cdot$yr exposure and 95% confidence limits assuming zero background events, shown in terms of the interaction cross-section ($\overline\sigma_\psi$) and DM particle mass ($m_\chi$). Interactions with a light mediator are shown in the left column (panels a and c), while those with a heavy mediator are shown in the right column (panels b and d) (see Sec. \ref{['sec:dm-theory']} for details). The top row (panels a and b) shows the first four selected MOFs, while the bottom one (panels c and d) shows the remaining three. The gray areas are those excluded by previous direct detection experiments Essig:2015cdaSENSEI:2019ibbDarkSide:2018ppuDAMIC:2019dcn and by constraints from astrophysical observations Chang:2019xva. The proportion of the chiral phase space has been set for all MOFs to $\kappa=0.16$. Data for InF$_3$(bpy) are reproduced from the literature Romao:2023zqf.