We report on our experimental evidence of a substantial geometrical ingredient characterizing the problem of incipient dissipation in high-$T_c$ superconductors (HTS’s): high-resolution studies of differential resistance-current characteristics in the absence of magnetic field enabled us to identify and quantify the fractal dissipative regime inside which the actual current-carrying medium is an object of fractal geometry. The discovery of a fractal regime proves the reality and consistency of a critical-phenomena scenario as a model for dissipation in inhomogeneous and disordered HTS’s, gives the experimentally based value of the relevant finite-size scaling exponent, and offers some interesting new guidelines to the problem of pairing mechanisms in HTS’s.

• Received 18 February 1999

DOI:https://doi.org/10.1103/PhysRevB.60.3100