Order-Parameter Anisotropies in the Pnictides - An Optimization Principle for Multi-Band Superconductivity

TL;DR

This paper proposes an optimization principle based on electron interactions to explain the symmetry and nodal behavior of superconducting gaps in multi-band ferropnictide materials.

Contribution

It introduces a novel optimization framework linking electron interactions to superconducting gap symmetry in multi-band systems.

Findings

Gap symmetry is determined by optimization between pairing wave function and repulsive interactions.

Functional renormalization group calculations support the optimization principle.

Nodal versus nodeless gap behavior is explained by the proposed optimization mechanism.

Abstract

Using general arguments of an optimization taking place between the pair wave function and the repulsive part of the electron-electron interaction, we analyze the superconducting gap in materials with multiple Fermi-surface (FS) pockets, with exemplary application to two proto-type ferropnictide setups. On the basis of functional renormalization group (FRG) calculations for a wide parameter span of the bare interactions, we show that the symmetry of the gap and the nodal versus nodeless behavior is driven by this optimization requirement.