Pressure Dependence of Excitations of Liquid 4He

No Heading Confinement of liquid ⁴He in porous glasses increases its solidification pressure and suppresses the superfluid transition temperature T. It has been reported that a sufficiently high degree of confinement suppresses T to zero at high pressure, signifying a quantum phase transition. We evaluate the behaviour of the excitation spectrum at wave vectors Q < 2.3 Å^–1 at pressures well above 25 bar by calculating the dynamic structure factor, S(Q, E), using the theory of hybridization of one- and two-particle excitations. The aim is to explore whether well-defined excitations exist at high pressures, and whether there is some critical pressure at which they disappear. We find that as the pressure increases, the one-particle excitation energy is well-defined if its energy lies below the two-roton energy, and ceases to exist as a well-defined excitation if its energy lies above the two-roton energy. We relate these findings to potential inelastic neutron scattering measurements.