Time-reversal symmetry breaking state near the surface of an s± superconductor

Abstract

The structure of superconducting order parameter near the surface of a two-band superconductor with s± order parameter in the bulk is theoretically investigated. The main parameter of the surface, which determines the appropriate physics, is the coefficient of the interband scattering R12. For small R12, the superconducting order parameter is only suppressed to some extent near the surface for both bands. For intermediate and strong interband scattering, there are two possible nontrivial surface states of the order parameter: (i) purely real solution, where the symmetry of the superconducting state near the surface is changed from s± to conventional s++ and (ii) time-reversal symmetry breaking (TRB) state. In this state, the order parameters in the two bands acquire phases φ1,2(x)≠(0,π) upon approaching the surface. We argue that at low temperatures the TRB surface state can be more energetically favorable than the s±→s++ time-reversal symmetry conserving state (TR). For higher temperatures up to Tc only the TR state can exist. The transition between the two temperature regions is rather sharp. Signatures of the transition between the TRB and the TR surface states can be detected by the measurements of the local density of states and the angle-resolved density of states.

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