Super solid
At temperatures below 2.18 K, liquid 4He enters into a superfluid state and flows without any friction. The onset of superfluidity is associated with Bose-Einstein condensation where the 4He atoms condense into a single momentum state and acquire quantum mechanical coherence over macroscopic length scales. There is strong evidence for superfluidity in the Bose-Einstein condensation of alkali atoms. Counter-intuitively superfluid-like behavior is thought possible even in solid helium. Recent torsional oscillator measurements found evidence of super fluid flow in bulk solid 4He and solid 4He confined in porous media. There is evidence that this phenomenon may exist in solid hydrogen samples at sufficiently low temperatures. This new state of matter has received considerable theoretical and experimental attentions. Recent torsional oscillator experiments of three different groups confirmed the Kim and Chan's result independently but the underlying microscopic mechanism still remains unclear. With this discovery, we now know that all three states of matter -gas, liquid, and solid- can exhibit superfluid behavior. We will search for new supersolid systems in reduced dimension and study the effect of 3He impurities on the supersolid state to understand the nature of the supersolid.