Experiments with solid 4He

The possibility of supersolid behavior in 4He was predicted many years ago, but negative experiments in the 1970's removed motivation for further experimental efforts to explore the possibility until the work of Goodkind's group renewed attention. Kim and Chan found unambiguous evidence for a period shift in a torsional oscillator filled with solid 4He and this observation and its interpretation have created substantial interest in the study of solid 4He. Here, recent work with an experimental design that allows for superfluid 4He to be in direct contact with solid 4He off the melting curve will be discussed and evidence for the flow of helium atoms through a cell filled with solid 4He, caused by an applied chemical potential difference will be briefly reviewed.