Emergent quantum states and quantum phase transitions in 2D and 1D superconductors
We study superconductivity and superconductor-insulator transitions in extremely thin metal films and nanowires. We grow the thin films and nanowires in a dilution refrigerator under ultrahigh vacuum at cryogenic temperature and perform all the electronic measurements in situ. Since the samples never see ambient air and temperature, the method allows us to access monolayer thicknesses without worrying about oxidation, and examine the evolution of the electronic properties with increasing thicknesses, varying magnetic field, and incremental magnetic impurity densities, all on the same sample. The experiments have resulted in the surprising discovery of enhancement of superconductivity by parallel magnetic field in ultrathin Pb films.
d-tuned superconductor-insulator transitions
Jeffrey Parker et al, Europhysics Letters 2006
Parallel field enhancement of superconductivity
Jeffrey Gardner et al, Nature Physics 2011