Condensed Matter Seminars

We have observed superflow in both bulk solid He-4 and solid He-4 confined in porous media by torsional oscillator technique.[1] Below 0.25K non-classical rotational inertia appears as an abrupt drop in the resonant period of the torsional oscillator. The temperature dependence of the supersolid fraction is different from those found in liquid helium and weakly interacting alkali gases. The non-classical rotational inertia fraction is independent of the oscillation speed below an extremely small critical value of 10 um/s, above which strongly attenuated. The pressure dependence of the supersolid fraction in the low temperature limit reveals an intriguing maxium around 55 bars, whereafter the supersolid fraction monotonically decreases at least up to 136 bars and can be linearly extrapolated to zero at 170 bars. [1] E. Kim and M. H. W. Chan, Nature 427, 225 (2004); Science 305, 1941 (2004); J. Low Temp. Phys. 138, 859 (2005).