Indirect Magnetic-Field-Tuned Superconductor-Insulator Transitions and Weak Localization of Bosons of Quasi-Two Dimensional Metal Films

摘要

Magnetic field and electrostatically tuned superconductor-insulator (SI)transitions of ultrathin metal films with levels of disorder that place themnear the disorder-tuned SI transition appear to be direct, continuous quantumphase transitions. When films with lower levels of disorder are subjected to aperpendicular magnetic field, instead of a direct transition, a mixedsuperconductor-nonsuperconductor regime emerges at the lowest temperatures. Thezero temperature limit of the resistance is either insulating orsuperconducting, depending upon the value of the field, suggesting that thebehavior in this limit is governed by percolation physics. At high fields andlow temperatures, in the nominally insulating regime, the resistance ratherthan the conductance is found to be a logarithmic function of temperaturecorresponding to predicitons for the weak localization of bosons.