Quantum matter consisting of light particles can stay liquid or gaseous without solidifying even at absolute zero. Such matter is termed a quantum liquid or quantum gas. The helium-3 system confined in a two-dimensional space has long been thought of as the only material which stays gaseous at the ground state.
Here, the group of Prof. Hiroshi Fukuyama of the Graduate School of Science, The University of Tokyo and Dr. Daisuke Sato of the Japan Society for the Promotion of Science has discovered that the system liquefies with the lowest density ever found by measuring heat capacities of monolayers of helium-3 adsorbed on a graphite surface down to ultra-low temperatures around two thousandths of a Kelvin. This finding contradicts conventional wisdom and presses theorists to reconsider this problem or to reconstruct new theories.
Liquid helium occupies a unique position in many other quantum fluids in nature such as electrons in solids, nuclei, neutron stars, etc, since the quantum gas-liquid phase transition can be experimentally examined in detail only in this system. The present work has brought us a new control parameter of the transition, which is dimensionality, and will deepen our understanding of nature.
D. Sato, K. Naruse, T. Matsui, and Hiroshi Fukuyama,
“Observation of Self-Binding in Monolayer 3He”,
Physical Review Letters (2012): 235306-1-4, doi: 10.1103/PhysRevLett.109.235306.
Source: University of Tokyo