Monolayers of 3He on the Surface of Bulk Superfluid 4He

We have used quantum evaporation to investigate the two-dimensional fermion system that forms at the free surface of (initially isotopically pure) 4He when small quantities of 3He are added to it. By measuring the first-arrival times of the evaporated atoms, we have determined that the 3He-3He potential in this system is V_3S/k_B=(0.23+/-0.02) K nm^2 (repulsive) and estimated a value of m_3S=(1.53+/-0.02)m_3 for the zero-coverage effective mass. We have also observed the predicted second layer-state which becomes occupied once the first layer-state density exceeds about 0.6 monolayers.