Liquid-Solid Transition and Phase Diagram of ^4He Confined in Nanoporous Glass

TL;DR

This study investigates the phase transition of ^4He confined in nanoporous glass, revealing an elevated, temperature-independent freezing pressure and suggesting a localized Bose-Einstein condensation state due to nanopore confinement.

Contribution

It provides new insights into the liquid-solid phase boundary of ^4He in nanopores and proposes the existence of a localized BEC state caused by confinement effects.

Findings

Freezing pressure is elevated to 1.2 MPa below 1 K.

The L-S boundary is temperature-independent.

Evidence suggests a localized Bose-Einstein condensation state.

Abstract

We have studied the liquid - solid (L-S) phase transition of ^4He confined in nanoporous glass, which has interconnected nanopores of 2.5 nm in diameter. The L-S boundary is determined by the measurements of pressure and thermal response during slow cooling and warming. Below 1 K, the freezing pressure is elevated to 1.2 MPa from the bulk freezing pressure, and appears to be independent of temperature. The T-independent L-S boundary implies the existence of a localized Bose-Einstein condensation state, in which long-range superfluid coherence is destroyed by narrowness of the nanopores and random potential.