Torsional oscillator and synchrotron x-ray experiments on solid He4 in aerogel

X-ray diffraction experiments show that solid He4 grown in aerogel is highly polycrystalline, with an hcp crystal structure (as in bulk) and a crystallite size of approximately 100 nm. In contrast to the expectation that the highly disordered solid will have a large supersolid fraction, torsional oscillator measurements show a behavior that is strikingly similar to high purity crystals grown from the superfluid phase. The low temperature supersolid fraction is only ∼3×10-4, and the onset temperature is ∼100mK.