Vortex as a probe - suggested measurement of the order parameter structure in iron-based superconductors

TL;DR

This paper proposes using vortex-induced scattering effects in Fourier transformed scanning tunneling spectroscopy to distinguish between different pairing symmetries in iron-based superconductors, especially to detect sign changes in the order parameter.

Contribution

It introduces a novel method to probe the momentum-space structure of the superconducting order parameter using vortex scattering effects in impurity-induced transitions.

Findings

Vortex scattering enhances impurity transitions in simple s-wave superconductors.

In s+- superconductors, only intra-pocket transitions are affected by vortices.

The method can potentially identify sign changes in the order parameter.

Abstract

Impurities, inevitably present in all samples, induce elastic transitions between quasiparticle states on the contours of constant energy. These transitions may be seen in Fourier transformed scanning tunneling spectroscopy experiments, sorted by their momentum transfer. In a superconductor, anomalous scattering in the pairing channel may be introduced by magnetic field. When a magnetic field is applied, vortices act as additional sources of scattering. These additional transition may enhance or suppress the impurity-induced scattering. We find that the vortex contribution to the transitions is sensitive to the momentum-space structure of the pairing function. In the iron-based superconductors there are both electron and hole pockets at different regions of the Brillouin zone. Scattering processes therefore represent intrapocket or interpocket transitions, depending on the momentum transfer in the process. In this work we show that while in a simple s-wave superconductors all transitions are enhanced by vortex scattering, in an s+- superconductor only intra-pocket transitions are affected. We suggest this effect as a probe for the existence of the sign change of the order parameter.