Quantum reflection, evaporation, and transport currents in ⁴He

We study transport currents induced by excited states in the surface and in bulk ⁴He. This requires the calculation of particle currents 〈n ĵ n〉 to second order in the excitation amplitudes. For that purpose, we extend a well-tested microscopic theory of inhomogeneous quantum liquids to find the currents created when either a quasiparticle propagates through the liquid, when atoms scatter off its surface, or when excitations evaporate atoms. Specifically, we look at the phonon lifetime and quantum reflection. We show that quantum reflection is sensitively affected both by details of the liquid surface profile and by many-body effects.