A resonant inelastic x-ray scattering study of the spin and charge excitations in the overdoped superconductor La1.77Sr0.23CuO4

TL;DR

This study uses resonant inelastic x-ray scattering to investigate spin and charge excitations in overdoped La1.77Sr0.23CuO4, revealing highly overdamped excitations with momentum-dependent spectral weight, supporting an itinerant electron model.

Contribution

It provides the first detailed RIXS analysis of overdoped La1.77Sr0.23CuO4, showing the excitations are overdamped and consistent with an itinerant picture, and predicts a new low-energy spin excitation branch.

Findings

Spin and charge excitations are highly overdamped.

Spectral weight and damping are momentum dependent.

Agreement with RPA susceptibility suggests itinerant behavior.

Abstract

We present a resonant inelastic x-ray scattering (RIXS) study of spin and charge excitations in overdoped La1.77Sr0.23CuO4 along two high-symmetry directions. The line shape of these excitations is analyzed and they are shown to be highly overdamped. Their spectral weight and damping are found to be strongly momentum dependent. Qualitative agreement between these observations and a calculated RPA susceptibility is obtained for this overdoped compound, implying that a significant contribution to the RIXS signal stems from a continuum of charge excitations. Furthermore, this suggests that the spin-excitations in the overdoped regime can be captured qualitatively by an itinerant picture. Our calculations also predict a new low-energy spin excitation branch to exist along the nodal direction near the zone center. With the energy resolution of the present experiment, this branch is not resolvable but we show that next generation of high-resolution spectrometers will be able to test this prediction.