MATERIALS SCIENCE COLLOQUIUM

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ABSTRACT: The interplay between superconductivity and localization in two-dimensional superconducting films can result in transformation of superconductivity into a peculiar insulating phase, the Cooper-pair insulator, where Cooper pairing still exists but propagation of the supercurrents is inhibited by disorder. These superconducting and insulating states are dual and demonstrate similar sequences of finite temperature transitions: metal - resistive state – global phase coherent superconducting state at the superconducting side and the corresponding metal - insulator (characterized by Arrhenius-type conductivity) - superinsulator transitions at the insulating side. We discuss the phase diagram in the critical region of the superconductor-insulator transition in the context of superconducting films and Josephson junction arrays. We present the experimental evidence for the superconductor-superinsulator duality demonstrating the dual vortex binding-unbinding Berezinskii-Kosterlitz-Thouless (BKT) and charge-binding-unbinding BKT transitions. 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 Cooper pair dipole (CPD) environment. The energy gap, in the CDP spectrum below the BKT transition, gives rise to suppression of the tunneling current offering the microscopic mechanism for the superinsulating behavior.