Single electron effects and Bloch oscillations in high-TC superconductive tunneling junctions

We investigated the effects of single electron charging energy in high-TC superconductors. Various phenomena originated from Coulomb blockade were observable in c-axis NdBa2Cu3O7 −δ /PrBa2Cu3O7−δ /NdBa2Cu3O7−δ superconducting tunnel junctions. The current-voltage characteristics show a Coulomb gap for Cooper pair tunneling when the charging energy exceeds the Josephson coupling energy. A crossover from Coulomb blockade of Cooper pair tunneling to a supercurrent is observed when the ratio of Josephson coupling energy to charging energy is increased. We found a regime in which aspects of the Coulomb blockade of tunneling coexist with features typical of Josephson tunneling. Under microwave irradiation of frequency f, the dynamic resistance dV/ dI as a function of the current I showed sharp singularities at I=2nef, n= ±1, ±2,.... This behavior appears to be very similar to the one predicted by the semiclassical theory of Bloch oscillations.