Anomalous magnetoresistance in ultrathin Nb films

The normal-state conductivity of thin Nb films was studied as a function of temperature and magnetic field. At liquid-He temperatures, the behavior of the zero-field conductivity is in agreement with recent electronic transport theories in the presence of disorder. The magnetoresistance, however, shows some anomalous features that cannot be simply reconciled with known mechanisms. The suppression of superconductivity with increased sheet resistance is discussed in light of these findings.