Spin-Phonon Renormalization in CrSBr

Abstract

Direct experimental evidence of spin-phonon coupling in CrSBr is provided by the temperature dependent Cr L-edge resonant inelastic x-ray scattering (RIXS) spectra. Zone-center optical phonons are observed exclusively in the low-temperature antiferromagnetic phase as energy loss features. These phonon modes have energies of approximately, 43.5 meV and 43.1 meV for x-rays that are {\sigma}-polarized along the a and b axes, respectively. While a phonon mode of approximately 42.1 meV is observed under {\pi}-polarization. Density functional theory and phonon mode calculations identify these features as bond-bending optical phonon modes arising in the RIXS spectra. Room temperature melting of these low-energy RIXS peaks is explained in terms of a spin-phonon renormalization effect on the L-edge electron-phonon RIXS mechanism.