Penetration depth measurements as a test for time-reversal breaking states in unconventional superconductors

We examine the possibility of nonmagnetic impurity-induced time-reversal breaking in unconventional superconductors. We determine the phase diagram for impurity-induced broken-T-symmetry states, in a model in which a dominant unconventional order parameter is present along with a subdominant conventional one. We find that, under such conditions, a time-reversal breaking state is always possible in a wide range of impurity concentrations at sufficiently small temperatures. We determine the effect that the transition into such a phase has on the temperature dependence of the penetration depth. Our results suggest that such bulk, broken T-symmetry states could be detected by penetration depth measurements in very dirty samples. copyright 1997 The American Physical Society