April 22 (Friday) 1:10-2:10pm, LCD 104
Robert Hallock is a Distinguished professor of Physics at the University of Massachusetts in Amherst. His research is in the general area of experimental Condensed Matter Physics, with an emphasis on low temperature phenomena, particularly liquid helium, liquid helium films, and solid helium. About 40 years ago it was predicted that it might be possible for solid helium, 4He , to display some of the properties of a superfluid, thus there might be a supersolid. Experiments in the mid to late 1970’s were negative and the prediction languished. Then in 2004 an experiment was done that was interpreted as positive evidence for the presence of a supersolid in solid helium. But, the interpretation has been controversial and other evidence complicates the picture. Our experiments are conceptually different from all the others and may provide substantial evidence for superfluid behavior in solid 4He. Recent theoretical predictions, which differ substantially from the original theory of 40 years ago, are regarded as very consistent with the observations. We will begin with a brief discussion of some of the remarkable properties of superfluid 4He and then discuss experiments on solid 4He . The subject is a good example of how understanding of a physical system evolves, which is often nothing like the tidy stories one reads about in books.