The first unequivocal experimental evidence of a superfluid state in 2D 4He films
— Read on phys.org/news/2021-10-unequivocal-experimental-evidence-superfluid-state.html

From the linked article:

“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.

Researchers at Korea Advanced Institute of Science and Technology (KAIST) have recently improved on these measurements by gathering the first unequivocal experimental evidence of a superfluid state in 2D 4He films on a graphite substrate. Their findings, published in Physical Review Letters, suggest that the second layer of 4He films could be a highly promising candidate for hosting superfluid and supersolid phases.”