Evidence for Dynamic Phase Separation and High Energy Spin Dynamics in underdoped La$_{2-x}$Sr$_x$CuO$_4$ from Resonant Inelastic X-Ray Scattering

TL;DR

This study uses resonant inelastic X-ray scattering to reveal dynamic phase separation and complex high-energy spin excitations in underdoped La$_{2-x}$Sr$_x$CuO$_4$, highlighting inhomogeneous spin states.

Contribution

It provides direct momentum-resolved evidence of high-energy spin excitations and dynamic inhomogeneous spin states in underdoped cuprates, expanding understanding of their magnetic properties.

Findings

High-energy spin branch coexists with low-energy branch in LSCO.

RIXS measurements match neutron data for undoped La$_2$CuO$_4$.

Evidence of dynamic inhomogeneous spin states in LSCO.

Abstract

We probe the collective magnetic modes of La$_2$CuO$_4$ (LCO) and underdoped La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) by momentum resolved Resonant Inelastic X-ray Scattering (RIXS) at the Cu $L_3$ edge. In LCO the single magnon dispersion measured by RIXS coincides with the one determined by inelastic neutron scattering. For LSCO the spin dynamics shows a branch dispersing up to $\sim$400 meV coexisting with a branch at lower energy. Only the latter has been observed with neutrons so far and is considered a key signature of doped cuprates. The presence of the high-energy branch indicates that LSCO is in a dynamic inhomogeneous spin state.