Utility of Zeeman Perturbed Nuclear Quadrupolar Resonance in Probing Time Reversal Symmetry Breaking: A Case Study on CDW RbV3Sb5

Evidence for Time Reversal Symmetry Breaking (TRSB) has been reported for a number of superconducting [1] and charge-density-wave systems [2], which has potentially important implications for the nature of the order parameter, including the possibility for bulk topological superconducting states. Nevertheless, conflicting experimental results call for an expansion of the suite of probes sensitive to TRSB. Here, we examine the utility of Zeeman perturbed nuclear quadrupolar resonance in probing orbital magnetism and apply this technique to the CDW state of RbV3Sb5 as a test system. It is well-established that a small magnetic field in a quadrupolar system induces modulation of the spin-spin relaxation (T2) decay curve, even for the common case that inhomogeneous broadening precludes spectral resolution of the effects. The frequency and amplitude of the modulation —and thus the sensitivity of the method— is controlled by the field vector B, asymmetry parameter η, and T2. We explore this parameter space through a combination of simulations and experiment. No evidence for echo modulations were detected for the Sb sites. At present, we establish an upper bound for orbitally-generated fields of order 1 G in the CDW state of RbV3Sb5.

1.Ghosh et al., J. Phys.: Condens. Matter 33, 033001 (2021).

2. Xing et al., Nature 631, 60–66 (2024).