Giant Resonance Raman Scattering via Anisotropic Excitons in ReS₂

Anisotropic two-dimensional (2D) semiconductors have recently emerged as a promising platform for polarization-controlled Raman amplification. In this study, we probe energy-dependent resonant Raman scattering in few-layer ReS2 under different polarization configurations. We identify two distinct excitation regimes, each characterized by a resonance condition, where either the pump or the Stokes photon energy aligns with an excitonic transition. A two-order-of-magnitude enhancement in Raman intensity is observed when the pump energy is tuned near the exciton resonance. Under Stokes-resonant conditions, additional Raman lines accompanied by excitonic photoluminescence are observed, suggesting the participation of non-Bloch intermediate states in the scattering process. These findings shed light on the influence of excitons in modulating nonlinear optical phenomena in anisotropic 2D materials, offering valuable insights for the design of tunable photonic and optoelectronic devices based on anisotropic layered materials.