Collective nature of spin excitations in superconducting cuprates probed by resonant inelastic x-ray scattering

TL;DR

This study uses resonant inelastic x-ray scattering to investigate spin excitations in high-temperature superconducting cuprates, revealing their collective magnetic nature across various doping levels.

Contribution

The paper provides experimental evidence that spin excitations in doped cuprates are predominantly collective magnetic modes, challenging recent theoretical suggestions of incoherent particle-hole contributions.

Findings

Spin excitation energy is independent of incident photon detuning across doping levels.

Majority of RIXS profiles originate from magnetic collective modes.

Results support the magnetic collective mode interpretation over incoherent particle-hole excitations.

Abstract

We used resonant inelastic x-ray scattering (RIXS) with and without analysis of the scattered photon polarization, to study dispersive spin excitations in the high temperature superconductor YBa2Cu3O6+x over a wide range of doping levels (0.1 < x < 1). The excitation profiles were carefully monitored as the incident photon energy was detuned from the resonant condition, and the spin excitation energy was found to be independent of detuning for all x. These findings demonstrate that the largest fraction of the spin-flip RIXS profiles in doped cuprates arises from magnetic collective modes, rather than from incoherent particle-hole excitations as recently suggested theoretically [Benjamin et al. Phys. Rev. Lett. 112, 247002(2014)]. Implications for the theoretical description of the electron system in the cuprates are discussed.