Finding the Supersolid

Liquid helium 4 undergoes a phase transition into a superfluid at low temperatures. Owing to its quantum nature, the solid phase of helium 4 has been suggested to host a similar type of Bose-condensed state, supporting frictionless mass flow. This unique phenomenon has been termed supersolidity. In the past decade, the existence of supersolidity has been alternately confirmed and disproved experimentally. The controversy originates from the fact that a small supersolid signal can be overshadowed by large elastic effects arising from an anomaly in the shear modulus of the solid. Using a novel experimental approach, with specially-designed multi-mode torsional oscillators, we were able to accurately distinguish between the different contributions for the first time, and discovered a small frequency-independent signal, as expected in the presence of a supersolid phase. I will discuss the significance of our results in the broader context of the field's current state.