Superglass Phase ofHe4

We study different solid phases of ${}^4\mathrm{He}$, by means of path integral Monte Carlo simulations based on a recently developed worm algorithm. Our study includes simulations that start off from a high-$T$ gas phase, which is then “quenched” down to $T=0.2\mathrm{K}$. The low-$T$ properties of the system crucially depend on the initial state. While an ideal hcp crystal is a clear-cut insulator, the disordered system freezes into a superglass, i.e., a metastable amorphous solid featuring off-diagonal long-range order and superfluidity.