Quantum effects in the structural properties of supercriticalHe4

Neutron-diffraction measurements have been performed on supercritical fluid He4 in the 1485 K temperature range along an isochore passing close to the lower point. The quantum nature of the particle pair distribution functions is analyzed by comparing our results with classical molecular-dynamics simulations. Deviations from classical behavior are seen to persist up to T=85 K although they are much larger at lower temperatures. A measure of these deviations is obtained through an empirical parameter describing quantum delocalization around the classical positions. Limiting low-temperature behavior of this parameter is discussed and compared with direct experimental evidence of low-temperature quantum delocalization obtained from the particle momentum distribution. © 1994 The American Physical Society.