  We report transport measurements on superconducting wire networks which
provide the first experimental evidence of a new localization phenomenon
induced by magnetic field on a 2D periodic structure. In the case of a
superconducting wave function this phenomenon manifests itself as a depression
of the network critical current and of the superconducting transition
temperature at a half magnetic flux quantum per tile. In addition, the strong
broadening of the resistive transition observed at this field is consistent
with enhanced phase fluctuations due to this localization mechanism.
