UC Davis

Nitrogen-vacancy color centers in diamond have attracted broad attention as quantumsensors for AC mangetic field. Here we develop a quantum diamond spectrometer for both ambient condition and under pressure in diamond anvil cells. Optically based nuclear magnetic resonance has been achieved and various AC sensing methods have been demonstrated. A clear signal from precessing 13C spins in the diamond lattice has been found. The synchronized readout sensitivity at ambient and 3.6 GPa pressure are 1.9 and 7.6 nT/√Hz, respectively. In order to decrease the pressure inhomogeneity, a novel method – double quantum resonance – has been testified and discussed. Using conventional nuclear magnetic resonance approach, a rare earth insulator TmVO4, which is a model system to study nematic order and the roles played by nematic fluctuations, has been studied as a function of temperature and magnetic field direction orientation. We find that the magnetic shift tensor agrees quantitatively with direct dipolar coupling between the V nuclear moments and the Tm 4f moments. The spin-lattice relaxation rate exhibits a steep minimum for a field oriented 90◦ to the c axis, which is inconsistent with purely magnetic fluctuations. It is likely that both quadrupolar and magnetic fluctuations are present and drive spin-lattice relaxation.