Interplay of electron-phonon-spin coupling in CrSBr

The coupling of electronic, lattice, and magnetic degrees of freedom in Chromium Sulfur Bromide (CrSBr) promises the presence of tunable features that are desirable of the next-generation electronic and spintronic devices. This chalcogen-halide van der Waals magnetic semiconductor has been recently investigated using x-ray spectroscopy. Low temperature resonant inelastic x-ray scattering (RIXS) spectrum of CrSBr indicates the development of a low energy feature in the optic phonon frequency range. In addition, the RIXS intensity is suppressed as the material is warmed up to room temperature. We utilize a combination of density functional theory (DFT using Quantum Espresso), PHONONPY, and SMODES to characteristic the phonon dispersion, phonon mode symmetry, and electron-phonon coupling of bulk CrSBr to identify the optic bands that could contribute to the low energy phonon RIXS signature. Next, with input from our DFT computations, we develop an electron-phonon-spin coupling theory to formulate a conceptual picture of spin-phonon frequency renormalization. The spin-phonon theory, when applied in conjunction with a UCL based RIXS electron-phonon theory, explains the origins of the RIXS spectrum suppression with increasing temperature.