Transition into a low temperature superconducting phase of unconventional pinning in Sr2RuO4

We have found a sharp transition in the vortex creep rates at a temperature T* = 0.05T(c) in a single crystal of Sr2RuO4 (T-c = 1.03 K) by means of ma gnetic relaxation measurements. For T < T* the initial creep rates drop to undetectably low levels. One explanation for this transition into a phase w ith such extremely low vortex creep is that the low-temperature phase of Sr 2RuO4 breaks; time reversal symmetry. In that case, degenerate domain walls separating discreetly degenerate states of a superconductor can act as ver y strong pinning centers. (C) 1999 Elsevier Science B.V. All rights reserve d.