Resonance Raman Scattering and Anomalous Anti-Stokes Phenomena in CrSBr

TL;DR

This paper investigates the vibrational and optical properties of CrSBr, revealing anomalously high anti-Stokes Raman signals and exceptional stimulated Raman gain, advancing understanding of its unique electronic and vibrational interactions.

Contribution

It provides the first detailed analysis of anti-Stokes phenomena and Raman gain in CrSBr, highlighting its potential for nonlinear optical applications.

Findings

Anti-Stokes to Stokes intensity ratio up to 0.8, higher than graphene and MoS2

Raman gain of 1×10^8 cm/GW, much higher than other 3D systems

Observation of layer-dependent anti-Stokes phenomena and excitation-dependent effects

Abstract

CrSBr, a van der Waals material, stands out as an air-stable magnetic semiconductor with appealing intrinsic properties such as crystalline anisotropy, quasi-1D electronic characteristics, layer-dependent antiferromagnetism, and non-linear optical effects. In this study, we investigate the differences between the absorption and emission spectra, focusing on the origin of the emission peak near 1.7 eV observed in the photoluminescence spectrum of CrSBr. Our findings are corroborated by excitation-dependent Raman experiments. Additionally, we explore the anti-Stokes Raman spectra and observe an anomalously high anti-Stokes to Stokes intensity ratio of up to 0.8, which varies significantly with excitation laser power and crystallographic orientation relative to the polarization of the scattered light. This ratio is notably higher than that observed in graphene ($\approx$ 0.1) and MoS$_2$ ($\approx$ 0.4), highlighting the unique vibrational and electronic interactions in CrSBr. Lastly, we examine stimulated Raman scattering and calculate the Raman gain in CrSBr, which attains a value of 1 $\times$ 10$^{8}$ cm/GW, nearly four orders of magnitude higher than that of previously studied three-dimensional systems.