Magnetic Properties of the Superconducting State of Iron-Based Superconductors

TL;DR

This paper demonstrates that dynamical spin susceptibility features can distinguish pairing symmetries in iron-based superconductors, highlighting the magnetic resonance as a key indicator of the extended s-wave pairing and correlating theoretical calculations with experimental data.

Contribution

It provides a method to identify pairing symmetry using spin susceptibility features and confirms the extended s-wave symmetry in iron-based superconductors through theoretical and experimental comparison.

Findings

Magnetic resonance is a signature of extended s-wave pairing.

Resonance weakens in mixed superconducting and magnetic states.

Calculated NMR relaxation rates agree with experimental data.

Abstract

We show that features of the dynamical spin susceptibility can unambiguously distinguish between different pairing symmetries of the superconducting state in iron-based superconductors. A magnetic resonance is a unique feature for the extended $s_{x^2y^2}$-wave $\cos k_x\cos k_y$ pairing symmetry. It is present in the pure superconducting (SC) state, but weakens in the mixed SC and magnetically ordered state. We calculate the the RPA correction to the NMR spin relaxation rate $1/T_1$ and the Knight shift in the above states and show a good agreement with experimental results. Moreover, we argue that the energy dispersion of the magnetic resonance along c axis observed in neutron scattering experiments is also an indirect evidence supporting the $s_{x^2y^2}$ pairing symmetry.