Magnetic nature of the 500 meV peak in $\rm La_{2-x}Sr_{x}CuO_4$ observed with resonant inelastic x-ray scattering at the Cu $K$-edge

TL;DR

This study investigates the 500 meV peak in La2-xSrxCuO4 using RIXS, revealing its magnetic origin as a two-magnon excitation with temperature and doping dependence consistent with magnetic excitations.

Contribution

The paper provides comprehensive experimental evidence linking the 500 meV peak to two-magnon excitations and compares its behavior across temperature and doping levels with theoretical models.

Findings

Peak persists above Néel temperature but diminishes with temperature.

Peak energy shifts align with Raman two-magnon peaks.

Peak intensity decreases with doping, tracking spin correlation length.

Abstract

We present a comprehensive study of the temperature and doping dependence of the 500 meV peak observed at ${\bf q}=(\pi,0)$ in resonant inelastic x-ray scattering (RIXS) experiments on $\rm La_2CuO_4$. The intensity of this peak persists above the N\'eel temperature (T$_{N}$=320 K), but decreases gradually with increasing temperature, reaching zero at around T=500 K. The peak energy decreases with temperature in close quantitative accord with the behavior of the two-magnon $\rm B_{1g}$ Raman peak in $\rm La_2CuO_4$, and with suitable rescaling, agrees with the Raman peak shifts in $\rm EuBa_2Cu_3O_6$ and $\rm K_2NiF_4$. The overall dispersion of this excitation in the Brillouin zone is found to be in agreement with theoretical calculations for a two-magnon excitation. Upon doping, the peak intensity decreases analogous to the Raman mode intensity and appears to track the doping dependence of the spin correlation length. Taken together, these observations strongly suggest that the 500 meV mode is magnetic in character and is likely a two-magnon excitation.