Electronic transport and possible vortex states at T=0 in highly disordered ultrathin films of a-MoxSi1-x - art. no. 054523

We present transport properties of highly disordered thin and thick films o f amorphous MoxSi1-x at low temperatures. For thin films an anomalous peak and a subsequent decrease in the magnetoresistance (MR) have been observed on the insulating side (B>B-c) of the field-driven superconductor-insulator transition, while for thick films, or for thin films in parallel fields th e MR is always monotonic and positive. In B<B-c the metallic quantum-vortex -liquid phase is not evident, most likely absent. We interpret these result s in terms of the two-dimensional quantum phase transition. Alternative int erpretations of the data are also discussed.