Monolayers of He-3 on the surface of bulk superfluid He-4

We have used quantum evaporation to investigate the two-dimensional fermion system that forms at the free surface of (initially isotopically pure) He- 4 when small quantities of He-3 are added to it. By measuring the first-arr ival times of the evaporated atoms, we have determined that the He-3-He-3 p otential in this system is V-3S/k(B) = 0.23 +/- 0.02 K nm(2) (repulsive) an d estimated a value of m(3S) = (1.53 +/- 0.02)m(3) for the zero-coverage ef fective mass. We have also observed the predicted second layer-state which becomes occupied once the first layer-state density exceeds about 0.6 monol ayers. (C) 2000 Elsevier Science B.V. All rights reserved.