Search for Axions and Dark Photons Using Single Molecule Magnets

TL;DR

This work proposes using single-molecule magnets (SMMs) as detectors for sub-eV dark matter, focusing on dark photon and QCD axion models. The detection mechanism relies on DM-induced relaxation from metastable spin states triggering a magnetic avalanche that propagates through the crystal, encoding the deposited energy in a readout front. Dysprosium-based SMMs and Mn12-acetate provide complementary spectral coverage, enabling heightened sensitivity in DP and axion parameter spaces, respectively, with potential to surpass many existing bounds under realistic magnetic field and exposure conditions. The approach bridges chemistry, condensed-matter physics, and particle physics, and could be refined with stronger fields and improved material characterization to enhance practical reach.

Abstract

Molecular magnets, although analogous to familiar macroscopic magnets, offer a platform for next generation magnetic storage technologies with far higher data densities and prospective applications in quantum information science. When exposed to an external magnetic field, single molecule magnets enter a frustrated magnetic configuration that is exceptionally sensitive to low energy excitations. Energy deposited by a dark matter particle can trigger the relaxation of a metastable molecule, releasing Zeeman energy that subsequently propagates through neighboring molecules. This magnetic avalanche encodes the energy deposited in the initial excitation. By combining concepts from chemistry, condensed matter physics, and particle physics, we show that dysprosium and manganese molecules can achieve more than an order of magnitude improvement in sensitivity to dark photon and QCD axion models, respectively, compared with existing detection methods.

Figures (13)

• Figure 1: Sketch of the detection mechanism proposed in the paper. From left to right: the DM particle hits one of the molecules in the metastable state, which relaxes, releasing the Zeeman energy stored, which then propagates to the neighboring molecules, as shown by the red dashed circle increasing in size, in a process known as magnetic avalanche.
• Figure 2: It illustrates the dinuclear dysprosium. The dark blue spheres represent the dysprosium nuclei, the purple circles the oxygen atoms, and the light blue spheres the nitrogen.
• Figure 3: Figure displaying Dy$^{\text{III}}$. The dysprosium atom is in dark blue, oxygen in purple, and nitrogen in light blue. Highlighted in orange is the helical helicity center for the compound, which drives the compound's chiral features.
• Figure 4: The potential felt by an SMM molecule, FIG.\ref{['drawing1']} shows the potential without an external magnetic field, picturing the degenerate vacuum, while FIG.\ref{['drawing2']} pictures one of the vacuum lifted due to the presence of an external magnetic field. The mechanism proposed focuses on the latter.
• Figure 5: Velocity dependence on the deposited energy based on Eq. \ref{['eq-velocity']}. The behavior is as expected: the greater the energy deposited, the higher the velocity. The red dot shows the expected velocity for an energy deposition around $10^{-2}$eV. This plot is calculated for a Zeeman energy of $10^{-4}$eV for an anisotropic energy barrier of $U = 100$ K. The velocity also depends on how much Zeeman energy is stored, which means that the general behavior will change by changing the temperature at which the sample is kept.