Theory of Magnetic Fluctuations in Iron Pnictides

TL;DR

This paper investigates magnetic fluctuations in iron pnictides to understand their superconducting pairing symmetry, proposing a specific gap structure and predicting experimental signatures like resonance peaks and neutron scattering patterns.

Contribution

It introduces a novel extended s_{xy} gap model with line nodes and predicts distinctive magnetic fluctuation signatures in iron pnictides.

Findings

Evolution of spin-lattice relaxation rate matches experimental data

Prediction of a sharp resonance at (,) in the superconducting state

Modulated c-axis intensity in neutron scattering as a testable signature

Abstract

Magnetic fluctuations in an unconventional superconductor (U-SC) can distinguish between distinct proposals for the symmetry of the order parameter. Motivated thereby, we undertake a study magnetic fluctuations in Iron pnictides, tracking their evolution from the incoherent normal, pseudogapped metal, to the U-SC state. Within our proposal of extended-s-plus s_{xy} inplane gap with proximity-induced out-of-plane line nodes, (i) we describe the evolution of the spin-lattice relaxation rate, from a non-Korringa form in the normal state, to a power-law form in the U-SC in good agreement with experiment, and (ii) we predict a sharp resonance in the U-SC state along (\pi,\pi), but not along (\pi/2,0), along with modulated c-axis intensity in inelastic neutron scattering work as a specific and testable manifestation of our proposal.