Random Interactions

Vortex and charge BKT transitions in disordered superconductor thin films

by Mr. Sarath Sankar (TIFR, Mumbai)

Thursday, October 26, 2017 from to (Asia/Kolkata)
at A 304
There is strong experimental evidence for the surviving of cooper pairs beyond the critical temperature for superconductivity in disordered superconducting thin films. This emphasizes the role of phase fluctuations in the superconductor to insulator transitions (SIT). Magnetoresponse near the SIT shows various surprising behaviors. We study the shrinking of superconducting islands in a magnetic field using a disordered boson model. We then construct an effective Josephson junction model with field dependent parameters and obtain the magnetoresistance and superfluid stifness in three extreme parameter regimes. In two of these regimes we see that a vortex BKT transition and a modification of it by strong phase disorder plays a crucial role. We show that the recently reported phenomenon of superinsulation can be understood as a charge BKT transition. Strong disorder is again shown to alter the critical behavior, resulting in the Vogel-Fulcher-Tamann(VFT) behavior- a characteristic of glasses. We attribute this glassy behavior to the freezing phenomenon of charge dipole excitations.