Theoretical approach to direct resonant inelastic x-ray scattering on magnets and superconductors

TL;DR

This paper explores how resonant inelastic x-ray scattering (RIXS) can be used to investigate orbital properties, magnetic excitations, and superconducting gaps in unconventional high-temperature superconductors, providing insights into their pairing mechanisms.

Contribution

It presents a theoretical framework demonstrating how direct RIXS spectra can reveal orbital correlations, magnetic excitations, and superconducting gap features in complex materials.

Findings

RIXS spectra can distinguish different orbital orders in magnetic systems.

RIXS can measure superconducting gap magnitude and nodal points.

The approach helps identify pairing symmetries in high-temperature superconductors.

Abstract

The capability to probe the dispersion of elementary spin, charge, orbital, and lattice excitations has positioned resonant inelastic x-ray scattering (RIXS) at the forefront of photon science. In this work, we will investigate how RIXS can contribute to a deeper understanding of the orbital properties and of the pairing mechanism in unconventional high-temperature superconductors. In particular, we will show how direct RIXS spectra of magnetic excitations can reveal long-range orbital correlations in transition metal compounds, by discriminating different kind of orbital order in magnetic and antiferromagnetic systems. Moreover, we will show how RIXS spectra of quasiparticle excitations in superconductors can measure the superconducting gap magnitude, and reveal the presence of nodal points and phase differences of the superconducting order parameter on the Fermi surface. This can reveal the properties of the underlying pairing mechanism in unconventional superconductors, in particular cuprates and iron pnictides, discriminating between different superconducting order parameter symmetries, such as $s$, $d$ (singlet pairing) and $p$ wave (triplet pairing).