The Normal-Superconducting Phase Transition in ZeroMagnetic Field; .

The fields of condensed-matter physics and materialsscience entereda new era with the discovery of high-temperaturesuperconductors more than twodecades ago. However, despite thelarge volume of work published on their properties,and despitetheir many uses, there is surprisingly littleagreement in thecondensed matter community regarding one of theirmost fundamentalbehaviors: the normal-superconducting phasetransition. This book describes investigations ofthe superconductingphase transition of YBCO thin films in zero magneticfield. Simple voltage vs. current curves at temperatures closeto the transition temperature show that thestandard scaling analysisfails at low currents, contrary to what is widelyaccepted -- but that there isevidence for the phase transition at higher currents. At lower currents, there are significant finite-sizeeffects due tothe thickness of the films. The crossover tofrom three-dimensional to two-dimensionalbehavior occurs even in thick films, andobscures the transition in zero field. Thiseffect would also occur in a magnetic field, and mayexplain thewide range of critical exponents found in the literature.