Superconductor Superinsulator- Duality: Experiment on ultrathin TiN films and Theory
|Date/Time:||Thursday, 10 Nov 2011 - Thursday, 10 Nov 2011|
|Location:||ROOM 5 Physics|
|Channel:||Condensed Matter Physics|
By fine-tuning disorder, the ultrathin titanium nitride film (with the thickness less than the superconducting coherence length) can be transformed from superconductor to insulator. We observe the vortex binding-unbinding Berezinskii-Kosterlitz-Thouless (BKT) transition at the superconducting side, where the high-temperature resistive state of the film turns into a phase-coherent superconducting state. We find a dual charge-binding-unbinding BKT transition at the insulating side. The observed low-temperature phase of the charge-BKT transition is the strongly correlated superinsulating state, which at very lowest temperatures terminates the Cooper pair insulator with the activated type conductivity.
We discuss the fundamental aspect of the superinsulation-superconductivity duality in the framework of Heisenberg uncertainty principle. On the microscopic level, considering the charge transfer in two-dimensional Josephson junction arrays, we observe that the tunneling current in their insulating state is ensured by the relaxation mediated by the electron-hole dipole environment. The energy gap, appearing in the electron-hole spectrum below the BKT transition, gives rise to suppression of the tunneling current offering the microscopic mechanism for the superinsulating behavior.