Signatures of strong correlation effects in RIXS on Cuprates

TL;DR

This paper demonstrates that the anomalous hardening of spin excitations in doped cuprates observed in RIXS experiments can be explained by strong coupling physics within the t-t'-t''-J model without additional terms, highlighting the role of doping-dependent bandwidth.

Contribution

It shows that the hardening effect in RIXS on cuprates arises from strong coupling physics and doping-dependent bandwidth, using Slave-Boson mean field theory on the t-t'-t''-J model, without extra three-site terms.

Findings

Qualitative agreement with experimental spin excitation spectra

Doping-dependent bandwidth explains the hardening effect

Interplay between particle-hole and paramagnon excitations discussed

Abstract

Recently, spin excitations in doped cuprates are measured using the resonant inelastic X-ray scattering (RIXS). The paramagnon dispersions show the large hardening effect in the electron-doped systems and seemingly doping-independence in the hole-doped systems, with the energy scales comparable to that of the antiferromagnetic magnons. This anomalous hardening effect was partially explained by using the strong coupling t-J model but with a three-site term(Nature communications 5, 3314 (2014)). However we show that hardening effect is a signature of strong coupling physics even without including this extra term. By considering the t-t'-t"-J model and using the Slave-Boson (SB) mean field theory, we obtain, via the spin-spin susceptibility, the spin excitations in qualitative agreement with the experiments. These anomalies is mainly due to the doping-dependent bandwidth. We further discuss the interplay between particle-hole-like and paramagnon-like excitations in the RIXS measurements.