Dynamical spin susceptibility in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>La</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>CuO</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:mrow></mml:math> studied by resonant inelastic x-ray scattering
H. C. Robarts, Mirian García‐Fernández, Jiemin Li, Abhishek Nag, A. C. Walters, N. E. Headings, S. M. Hayden, Ke‐Jin Zhou
Abstract
Resonant inelastic x-ray scattering (RIXS) is a powerful probe of elementary excitations in solids. It is now widely applied to study magnetic excitations. However, its complex cross section means that RIXS has been more difficult to interpret than inelastic neutron scattering (INS). Here we report $\ensuremath{\sim}37$ meV resolution RIXS measurements of the magnetic excitations in ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4}$, the antiferromagnetic parent of one system of high-temperature superconductors. At high energies ($\ensuremath{\sim}2$ eV), the RIXS spectra show angular-dependent $dd$ orbital excitations in agreement with previous RIXS studies but show new structure. They are interpreted with single-site multiplet calculations. At low energies ($\ensuremath{\lesssim}0.3$ eV), we model the wave-vector-dependent single magnon RIXS intensity as the product of the calculated single-ion spin-flip RIXS cross section and the dynamical structure factor $S(\mathbf{Q},\ensuremath{\omega})$ of the spin-wave excitations. When $S(\mathbf{Q},\ensuremath{\omega})$ is extracted from our data, the wave-vector-dependence of the single-magnon pole intensity shows a similar variation to that observed by INS. Our results confirm that suitably corrected RIXS data can yield the genuine wave-vector and energy dependence of $S(\mathbf{Q},\ensuremath{\omega})$ for a cuprate antiferromagnet. In addition to spin waves, our data show structured multimagnon excitations with dispersing peaks in the intensity at energies higher than the single-magnon excitations.