Solid-State Nuclear Magnetic Resonance Search for Axion-like Dark Matter with Broadband SQUID Magnetometry

We report the results of an experimental search for ultralight axion-like dark matter in the mass ranges 18.9–20.6 and 21.6–21.9 neV. The Cosmic Axion Spin Precession Experiment-electric probes the axion-nuclear electric dipole moment coupling. We perform solid-state nuclear magnetic resonance on 207Pb spin ensembles which reside in a polarized ferroelectric crystal. The background axion-like dark matter field induces an oscillating torque on the 207Pb spins via the electric dipole moment coupling gd. The experiment is calibrated with pulsed magnetic resonance measurements covering two frequency bands (4.57–4.97 and 5.23–5.29 MHz) that correspond to the axion Compton frequencies associated with the identified axion mass ranges. By sweeping the leading magnetic field applied to the sample, we are able to detect the 207Pb nuclear magnetic resonance in these frequency ranges using a superconducting quantum interference device, inductively coupled to the sample with a broadband circuit. We establish the upper bounds |gd|<4×10−4 GeV−2 with 95% confidence in these frequency bands. Our results demonstrate the detection and small-tip angle calibration of low-field 207Pb nuclear magnetic resonance, allowing for sensitivity to axion-like dark matter in the nanoelectron-volt axion mass range.