Spin-orbit scattering and quantum metallicity in ultrathin Be films

We compare and contrast the low-temperature magnetotransport properties of ultrathin, insulating Be films with and without spin-orbit scattering SOS . Beryllium films have very little intrinsic SOS, but by “dusting” them with submonolayer coverages of Au, one can introduce a well-controlled SOS rate. Pure Be films with sheet resistance R RQ exhibit a low-temperature negative magnetoresistance MR that saturates to the quantum resistance RQ=h /e2. This high-field quantum metal phase is believed to represent a different ground state of the system. In contrast, the corresponding negative MR in Be/Au films is greatly diminished, suggesting that, in the presence of strong SOS, the quantum metal phase can only be reached at field scales well beyond those typically available in a low-temperature laboratory.