Inelastic Neutron Scattering Studies of the Spin and Lattice Dynamics in Iron Arsenide Compounds

TL;DR

This paper reviews neutron scattering studies on iron arsenide superconductors, highlighting the role of spin and lattice dynamics in understanding their unconventional superconductivity and magnetic properties.

Contribution

It provides comprehensive experimental insights into spin and lattice excitations, supporting the extended-s+/- wave symmetry model for superconductivity in iron arsenides.

Findings

Strong dispersive spin waves in parent compounds

Persistence of antiferromagnetic fluctuations in superconducting phase

Resonant spin excitation scales with Tc

Abstract

Neutrons have played an important role in advancing our understanding of the pairing mechanism and the symmetry of the superconducting energy gap in the iron arsenide compounds. Neutron measurements of the phonon density-of-state are in good agreement with ab initio calculations, provided the magnetism of the iron atoms is taken into account. However, the predicted superconducting transition temperatures are less than 1 K, making a conventional phononic mechanism for superconductivity highly unlikely. Measurements of the spin dynamics within the spin density wave phase of the parent compounds show evidence of strongly dispersive spin waves with exchange interactions consistent with the observed magnetic order. Antiferromagnetic fluctuations persist in the normal phase of the superconducting compounds, but they are more diffuse. Below Tc, there is evidence compounds that these fluctuations condense into a resonant spin excitation at the antiferromagnetic wavevector with an energy that scales with Tc, consistent with unconventional superconductivity of extended-s+/- wave symmetry.