Vacancies in solid 3He

Nuclear magnetic resonance studies of tunneling in quantum solids at very low temperatures

A review is given of recent NMR experiments at ultra-low temperatures that explore properties of quantum fluids and solids in regimes where unusual dynamics characterizes the low temperature behavior. It is shown how careful analysis of the NMR spin-spin and spin-lattice relaxation rates and spectral properties can determine fundamental thermodynamic features that are otherwise difficult to observe using standard thermodynamic methods. The review focuses on the observation of the diffusion of vacancies and isotopic impurities in solid hydrogen and solid helium by quantum tunneling at low temperatures.

Supersolid helium at high pressure

We have measured the pressure dependence of the supersolid fraction by a torsional oscillator technique. Superflow is found from 25.6 bar up to 136.9 bar. The supersolid fraction in the low temperature limit increases from 0.6% at 25.6 bar near the melting boundary up to a maximum of 1.5% near 55 bar before showing a monotonic decrease with pressure extrapolating to zero near 170 bar.