Helium at elevated pressures: Quantum liquid with non-static shear rigidity

TL;DR

This paper investigates the quantum liquid properties of helium under high pressure, demonstrating that helium remains a quantum liquid with non-static shear rigidity and phonon excitations over a wide pressure and temperature range.

Contribution

It introduces a phonon theory incorporating non-static shear rigidity to study helium's thermodynamic properties at elevated pressures, aligning well with experimental data.

Findings

Helium remains a quantum liquid at high pressures and temperatures.

Liquid helium exhibits both solid-like and quantum characteristics near melting.

Theoretical calculations agree with experimental heat capacity measurements.

Abstract

The properties of liquid helium have always been a fascinating subject to scientists. The phonon theory of liquids taking into account liquid non-static shear rigidity is employed here for studying internal energy and heat capacity of compressed liquid 4-He. We demonstrate good agreement of calculated and experimental heat capacity of liquid helium at elevated pressures and supercritical temperatures. Unexpectedly helium remains a quantum liquid at elevated pressures for a wide range of temperature supporting both longitudinal and transverse-like phonon excitations. We have found that in the very wide pressure range 5 MPa-500 MPa liquid helium near melting temperature is both solid-like and quantum.