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

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.