Finite size effects in thermodynamics: negative compressibility and global instability in two-phase systems

LTL Quantum Physics Seminar (Nanotalo). Speaker: Dr. Igor Todoshchenko (Aalto University, Finland).

We have for the first time measured directly the equilibrium melting pressure of helium-4 as a function of the crystal size. The negative compressibility of the liquid with an inclusion of solid seed has been generally predicted theoretically and demonstrated experimentally with helium-4 crystal superfluid system at 0.1 K. This two-phase system has been shown to be stable if the crystal size is large enough, which has been proven by the experiment. Crystal seeds that are too small spontaneously either melt completely or grow to a large enough size.