Precursor of Charge KTB Transition in Normal and Superconducting Tunnel Junction Array

We have measured the temperature dependence of zero-bias resistance R(T) of a two-dimensional array of small tunnel junctions with normal-state tunneling resistance of R N =32kΩ. Both in normal and superconducting states, R(T) showed square-root-cusp-type behavior, typical of the charge Kosterlitz-Thouless-Berezinskii (KTB) transition, in limited temperature ranges. The transition temperature in the superconducting state, estimated from R(T), is about four times larger than that in the normal state. We consider these features to be evidence of precursor effects of the charge KTB transition.