Finite-temperature localized state in superconducting films

Zero-resistance in superconductors is protected at finite temperatures by the global phase coherence, which by virtue of the uncertainty principle guarantees the dissipationless flow of Cooper pairs. In two-dimensional critically disordered films dual superinsulating state can form. In superinsulators coherent fluctuations of phase localize Cooper pairs leading to infinite-resistance at finite temperatures. I will present an experimental observation of the magnetic field-driven superconductor-superinsulator transition in disordered thin NbTiN films. Appearance of the superinsulator is detected by the abrupt upturn from the Arrhenius-type temperature dependence of the resistance, evidencing formation of the zero-conducting state at finite temperature. At relatively low magnetic fields we have found the critical divergent behavior of the resistance characteristic to charge Berezinskii–Kosterlitz–Thouless (BKT) transition, which is dual to the vortex BKT transition in superconducting state.