Persistent spin excitations in doped antiferromagnets revealed by resonant inelastic light scattering

TL;DR

This study clarifies how high-energy spin excitations in doped cuprates persist despite doping and are not directly linked to superconductivity, emphasizing the importance of light polarization in RIXS measurements.

Contribution

It demonstrates that RIXS at the Cu L3-edge accurately measures the spin dynamical structure factor when considering light polarization effects, and distinguishes the roles of high- and low-energy spin excitations in superconductivity.

Findings

High-energy spin excitations persist into the overdoped regime.

Low-energy excitations vary with doping and show ferromagnetic correlations.

High-energy excitations are not correlated with Tc.

Abstract

How coherent quasiparticles emerge by doping quantum antiferromagnets is a key question in correlated electron systems, whose resolution is needed to elucidate the phase diagram of copper oxides. Recent resonant inelastic X-ray scattering (RIXS) experiments in hole-doped cuprates have purported to measure high-energy collective spin excitations that persist well into the overdoped regime and bear a striking resemblance to those found in the parent compound, challenging the perception that spin excitations should weaken with doping and have a diminishing effect on superconductivity. Here we show that RIXS at the Cu L3-edge indeed provides access to the spin dynamical structure factor once one considers the full influence of light polarization. Further we demonstrate that high-energy spin excitations do not correlate with the doping dependence of Tc, while low-energy excitations depend sensitively on doping and show ferromagnetic correlations. This suggests that high-energy spin excitations are marginal to pairing in cuprate superconductors.