The first unequivocal experimental evidence of a superfluid state in 2D 4He films

Over the past few decades, some physicists worldwide have been trying to use the second layer of 4He films adsorbed on a graphite substrate to study the interplay between superfluid and supersolid phases of matter. Some teams have collected torsional oscillator (TO) measurements on this layer, including P.A. Crowell, F.W. Van Keuls and J.D. Reppy at Cornell University, as well as Dr. Jan Nyeki and his colleagues at Royal Holloway.