SUPERFLUID-INSULATOR TRANSITION IN HE-4 FILMS ADSORBED IN VYCOR GLASS

We have measured the heat capacity of He-4 films adsorbed in Vycor gla ss for temperatures down to 10 mK and coverages close to the critical coverage for the onset of superfluidity at T = 0. The data show that t he critical coverage corresponds to a mobility edge in the chemical po tential, below which the He-4 film is an insulator with a gap. We find no evidence for the existence of a gapless Bose glass phase.