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

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.

5 pages, 4 figures