OBSERVATION OF A VORTEX-GLASS PHASE IN A NARROW STRIP OF NB

The current-voltage isotherms of a narrow strip of Nb showed exponential behavior V/I is similar to exp[-I(-mu)] upon decreasing the temperature, below a phase with reduced linear resistivity; this phase became observable because of the reduction of collective pinning in narrow strips. This observation strongly suggests the occurrence of a vortex-glass transition in a conventional superconductor. Although no vortex-glass scaling behavior was observed, it means that the critical region is immeasurably small, which is expected from vortex-glass theory.