Charge Berezinskii-Kosterlitz-Thouless Transition in Superconducting NbTiN Films

Charge Berezinskii-Kosterlitz-Thouless transition in superconducting NbTiN films

Title: Charge Berezinskii-Kosterlitz-Thouless Transition in Superconducting NbTiN Films.
When: Friday, June 16, (2017), 12:00.
Place: Departamento de Física de la Materia Condensada, Facultad Ciencias, Module 3, Seminar Room (5th Floor).
Speaker: Tatyana I. Baturina, Institute of Semiconductor Physics Novosibirsk, Russia.

The superconductor-insulator transition (SIT) is a quantum phase transition in disordered superconducting films that occurs at the point where two inherently two-dimensional topological phase transitions – charage and vortex Berezinskii-Kosterlitz-Thouless (BKT) transitions – terminate each other. Applied magnetic fields can tune the SIT with high resolution, offering a window into relatively unexplored electronic functionalities. While the superconducting side of the SIT is well understood, the nature of the highly resistive superinsulating state that terminates two-dimensional superconductivity at the quantum critical point remains an open question.

I will present an experimental observation of the magnetic field-driven superconductor-superinsulator transition in disordered thin NbTiN films and demonstrate that the highly resistive state is an ordered charge BKT state. The observed nonmonotonic behaviour of the charge BKT transition temperature with magnetic field allows resolving a long-standing question of the origin of a giant magnetoresistance peak in the insulating state. These findings establish that BKT physics is a universal platform for the dual superconducting and superinsulating states.