Field induced Kosterlitz–Thouless transition in two-dimensional array of Josephson junctions

We present recent results on the magnetic field dependence of current–voltage characteristics (CVC) for an artificially prepared two-dimensional array of unshunted Nb–AlOx–Nb Josephson junctions. The results obtained from the measured CVC and critical current I C ( T , H ) differential magnetoresistance (DMR) R ( T , H ) = [ d V / d I ] I = I C ( T , H ) of the array are found to exhibit behavior compatible with field induced Kosterlitz–Thouless transition describing unbinding of vortex–antivortex pairs under applied magnetic field.