Competing ferromagnetic superconducting states in europium-based iron pnictides

TL;DR

This paper investigates the coexistence and competition of ferromagnetic and superconducting states in europium-based iron pnictides, revealing complex inhomogeneous phases influenced by magnetic fields and order parameters.

Contribution

It introduces the concept of inhomogeneous superconducting states, such as FFLO and textured phases, arising from magnetic interactions in europium-based iron pnictides.

Findings

Inhomogeneous superconducting states coexist with ferromagnetism.

The superconducting gap becomes V-shaped and inhomogeneous.

Magnetic and superconducting orders compete and intertwine.

Abstract

In europium-based iron pnictides superconducting Fe-planes can be influenced by a Zeeman field originated from the neighboring Eu-planes. The field tends to induce spin-density waves with a ferromagnetic average which coexists with the superconducting order by forming complementary patterns of the superconducting and magnetic order parameters in a Fulde-Ferrell-Larkin-Ovchinnikov phase and a two-dimensional textured-superconducting phase. The hard gap around the Fermi energy disappears in these fragile inhomogeneous superconducting states, which features, instead, V-shaped spin-resolved local density of states. The inhomogeneous states are also competing with either a homogeneous superconducting or a homogeneous ferromagnetic state, manifesting the intertwining influences of the magnetic orders in Fe and Eu planes, the spin-density wave band structure, and the superconducting pairing order.