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Non-linear conduction in the critical region of the superconductor-insulator transition in TiN thin films

We investigate experimentally electric transport at both the superconducting and insulating sides of the superconductor to insulator transition in TiN thin films. Relatively deeply on the superconducting side we find sharp transitions of R(T) to a zero-resistance state. Near the transition temperature the current-voltage I(V)-characteristics develops power-law type of non-linearity even for low currents. Close to the transition the superconducting state is destroyed by small magnetic fields and develops into an insulator with a thermally activated conductance. At low temperatures and low bias voltage we observe I ∝ Vα dependences in the insulating state with an exponent α rapidly growing with decreasing temperature. This behavior is strikingly similar to the V(I)'s observed in the superconducting state, if I and V are interchanged.

superconductor-insulator phase transition; Kosterlitz-Thouless transition

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