Order parameter sign-reversal near $s_\pm$-superconductor surface

TL;DR

This paper investigates how the superconducting order parameter and local density of states near a surface in an $s_$-wave superconductor can reverse sign, influenced by interband scattering, with implications for Fe-based high-temperature superconductors.

Contribution

It demonstrates that surface effects can induce a transition from $s_$ to conventional s-wave symmetry, depending on interband and intraband scattering, using selfconsistent calculations.

Findings

Surface can host a different superconducting symmetry from the bulk.

LDOS spectra are significantly affected by order parameter selfconsistency.

Sign-reversal of the order parameter near the surface depends on scattering parameters.

Abstract

The superconducting order parameter and LDOS spectra near an impenetrable surface are studied on the basis of selfconsistent calculations for a two band superconductor with nodeless extended s-+wave order parameter symmetry, as possibly realized in Fe-based high-temperature superconductors. It is found that for a wide range of parameters the spatial behavior of the order parameter at a surface is not reduced to a trivial suppression. If the interband scattering at a surface is of the order of the intraband one or dominates it, it can be energetically favorable to change the symmetry of the superconducting state near the surface from $s_{\pm}$ to conventional s-wave. The range of existing this surface conventional superconductivity is very sensitive to the relative values of interband and intraband pairing potentials. It is shown that the LDOS spectra near the surface can qualitatively differ upon calculating with and without taking into account the selfconsistency of the order parameter.