Predicted Nucleation of Domain Walls in px + ipy Superconductors by a Z2 Symmetry-Breaking Transition in External Magnetic Fields

We show that time reversal symmetry-breaking p(x) + ip(y) wave superconductors undergo several phase transitions subjected to an external magnetic field or supercurrent. In such a system, the discrete Z(2) symmetry can recover before a complete destruction of the order parameter. The domain walls associated with Z(2) symmetry can be created in a controllable way by a magnetic field or current sweep according to the Kibble-Zurek scenario. Such domain wall generation can take place in exotic superconductors like Sr2RuO4, thin films of superfluid He-3-A, and some heavy fermion compounds.