Spontaneous edge and corner currents in s plus is superconductors and time reversal symmetry breaking surface states

We present a study of the basic microscopic model of a s-wave superconductor with frustrated interband interaction. When frustration is strong, such an interaction gives raise to a s + is state. This is a s-wave super-conductor that spontaneously breaks time reversal symmetry. We show that in addition to the known s + is state, there is additional phase where the system's bulk is a conventional s-wave state, but superconducting surface states break time reversal symmetry. Furthermore, we show that s + is superconductors can have spontaneous boundary currents and spontaneous magnetic fields. These arise at lower-dimensional boundaries, namely, the corners in two-dimensional samples. This demonstrates that boundary currents effects in superconductors can arise in states which are not topological and not chiral according to the modern classification.

Automated summary

In this study, we investigate the microscopic model of a frustrated s-wave superconductor with interband interaction. We find that the strong frustration leads to an s + is state, which breaks the time reversal symmetry of the s-wave superconductor. Additionally, we identify another phase where the bulk of the system is in a conventional s-wave state, but the superconducting surface states break the time reversal symmetry. Moreover, we show that s + is superconductors can exhibit spontaneous boundary currents and magnetic fields at lower-dimensional boundaries, specifically at the corners of two-dimensional samples. These results demonstrate that boundary current effects in superconductors can arise in states that are not topological or chiral according to the modern classification.