# Tilting the balance towards d-wave in iron-based superconductors

## TL;DR

This paper investigates how magnetic fields and temperature influence the competition between s-wave and d-wave superconducting states in iron-based superconductors, revealing a universal phase boundary shape that favors d-wave pairing.

## Contribution

It provides a theoretical analysis of the phase boundary between nodal and nodeless superconducting states under magnetic field and temperature, specifically for s_ ext{±}-wave and d-wave pairing in iron-based superconductors.

## Key findings

- Universal cubic line shape of phase boundary near critical point
- Magnetic field and temperature favor d-wave state
- Quantitative model for competing pairing symmetries

## Abstract

The intricate interplay of interactions and Fermiology can give rise to a close competition between nodeless (e.g. s-wave) and nodal (e.g. d-wave) order in electronically driven unconventional superconductors. We analyze how such a scenario is affected by a Zeeman magnetic field $H_{\text{Z}}$ and temperature $T$. In the neighborhood of a zero temperature first order critical point separating a nodal from a nodeless phase, the phase boundary at low $H_{\text{Z}}$ and/or low $T$ has a universal line shape cubic in $H_{\text{Z}}$ or $T$, such that the nodal state is stabilized at the expense of the nodeless. We calculate this line shape for a model of competing s_\pm-wave and d-wave pairing in iron-based superconductors.