Nature of phase transitions of superconducting wire networks in a magnetic field.

We study {ital I}{minus}{ital V} characteristics of periodic square Nb wire networks as a function of temperature in a transverse magnetic field, with a focus on three fillings 2/5, 1/2, and 0.618 that represent very different levels of incommensurability. For all three fillings, a scaling behavior of {ital I}{minus}{ital V} characteristics is found, suggesting a finite temperature continuous superconducting phase transition. The low-temperature {ital I}{minus}{ital V} characteristics are found to have an exponential form, indicative of the domain-wall excitations. {copyright} {ital 1996 The American Physical Society.}