Abstract

Physica B 284 160-1 (2000)

Relative Evaporation Probabilities of ³He and ⁴He from the Surface of Superfluid ⁴He

J.P. Warren and C.D.H. Williams

School of Physics, University of Exeter, Exeter, EX4 4QL (UK).

(Submitted 17 June 1999)

We report a preliminary experiment which demonstrates that ³He atoms in Andreev states are evaporated by high-energy (E/k_B~10.2 K) phonons in a quantum evaporation process similar to that which occurs in pure ⁴He. Under conditions of low ³He coverage, high-energy phonons appear to evaporate ³He and ⁴He atoms with equal probability. However, we have not managed to detect any ³He atoms that have been evaporated by rotons, and conclude that the probability of a roton evaporating a ³He atom is less than 2% of the probability that it evaporates a ⁴He atom.

Keywords: liquid helium, surfaces, quantum evaporation, 2-D fermion systems.
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