NMR Signal Wipeout as a Probe of Quantum Fluctuations in TmVO4

TmVO4 is a model system for investigating the transverse field Ising model. This material undergoes ferroquadrupolar ordering below 2.3K due to an Ising-coupling between Tm quadrupolar couplings. This order can be destroyed via a transverse field along the crystalline c-axis. We probe the behavior of this system via V-51 NMR as a function of temperature and field along the c-axis. We find that the NMR spin echo intensity is dramatically reduced near the critical field, and that this behavior extends up to temperatures that exceed the critical temperature in zero transverse field. We argue that this behavior arises due to a unique hyperfine coupling that enables us to interpret the spin echo in terms of the time-dependence of the wavefunction of the environment of Tm quadrupolar moments. We confirm our behavior via spin lattice relaxation measurements that reveal a field-dependent gap opening above the critical field.