A straightforward way to determine the electric field gradient − principal axes frame (EFG-PAF) on single crystal samples with spin 3/2 nuclei is demonstrated. Nuclear quadrupole resonance (NQR) spectroscopy is used to determine the Rabi frequency for 35Cl in a single crystal of potassium chlorate (KClO3) by comparing the NQR signal for powder and single crystal samples. By exploiting the geometrical dependence of the Rabi frequency with respect to the excitation direction, EFG-PAF is readily determined. Furthermore, relaxation times T1 and T2∗ were measured at multiple temperatures ranging from 17K to 200K, extending the results of previous works to colder temperatures where new relaxation mechanisms become dominant. The experiments were performed in a cryogen-free cryostat, which posed distinct challenges compared to a conventional cryogenic cooling setup. The successful operation of the NQR probe within a cryogen-free cryostat has the potential to make the technique more accessible and widen applications.
@article{arxiv.2507.12279,
title = {Cryogenic spin 3/2 nuclear quadrupole resonance: Spin relaxation and electric field gradient via Rabi frequency goniometry},
author = {Ritik R. Modi and Karen L. Sauer},
journal= {arXiv preprint arXiv:2507.12279},
year = {2026}
}