Mechanism for a Pairing State with Time-Reversal Symmetry Breaking in Iron-Based Superconductors

TL;DR

This paper explores the possibility of a time-reversal-symmetry breaking s+id pairing state in iron-based superconductors, using a microscopic five-orbital model and combined theoretical methods.

Contribution

It introduces a microscopic framework for understanding s+id pairing states and identifies conditions favoring this phase in electron-doped iron pnictides.

Findings

s+id pairing state can emerge from competition between s_{+-} and d_{x^2-y^2} symmetries.

Enhanced pnictogen height and electron doping favor the s+id phase.

The combined RG and mean-field approach effectively identifies microscopic parameters for the s+id state.

Abstract

The multipocket Fermi surfaces of iron-based superconductors promote pairing states with both s_{+-}-wave and d_{x^2-y^2}-wave symmetry. We argue that the competition between these two order parameters could lead to a time-reversal-symmetry breaking state with s+id-pairing symmetry in the iron-based superconductors, and propose serveral scenarios in which this phase may be found. To understand the emergence of such a pairing state on a more rigorous footing, we start from a microscopic 5-orbital description representative for the pnictides. Using a combined approach of functional renormalization group and mean-field analysis, we identify the microscopic parameters of the s+id-pairing state. There, we find the most promising region for s+id-pairing in the electron doped regime with an enhanced pnictogen height.