Optical markers of magnetic phase transition in CrSBr

Here, we investigate the role of the interlayer magnetic ordering of CrSBr in the framework of ab initio calculations and by using optical spectroscopy techniques. These combined studies allow us to unambiguously determine the nature of the optical transitions. In particular, photoreflectance measurements, sensitive to the direct transitions, have been carried out for the first time. We have demonstrated that optically induced band-to-band transitions visible in optical measurement are remarkably well assigned to the band structure by the momentum matrix elements and energy differences for the magnetic ground state (A-AFM). In addition, our study reveals significant differences in electronic properties for two different interlayer magnetic phases. When the magnetic ordering of A-AFM to FM is changed, the crucial modification of the band structure reflected in the direct-toindirect band gap transition and the significant splitting of the conduction bands along the G-Z direction are obtained. In addition, Raman measurements demonstrate a splitting between the in-plane modes B22g/B23g, which is temperature dependent and can be assigned to different interlayer magnetic states, corroborated by the DFT+U study. Moreover, the B2 2g mode has not been experimentally observed before. Finally, our results point out the origin of interlayer magnetism, which can be attributed to electronic rather than structural properties. Our results reveal a new approach for tuning the optical and electronic properties of van der Waals magnets by controlling the interlayer magnetic ordering in adjacent layers.

Automated summary

In this study, we investigate the influence of interlayer magnetic ordering on the properties of CrSBr using ab initio calculations and optical spectroscopy techniques. Our combined approach allows us to accurately determine the nature of optical transitions and assign them to the band structure. We find significant differences in electronic properties between two interlayer magnetic phases, with changes in magnetic ordering leading to modifications in the band structure and the splitting of conduction bands. Raman measurements also reveal temperature-dependent splitting of in-plane modes, which can be attributed to different interlayer magnetic states.