Temperature induced modulation of resonant Raman scattering in bilayer 2H-MoS2

Abstract

The temperature evolution of the resonant Raman scattering from high-quality bilayer 2H-MoS_{2} encapsulated in hexagonal BN flakes is presented. The observed resonant Raman scattering spectrum as initiated by the laser energy of 1.96 eV, close to the A excitonic resonance, shows rich and distinct vibrational features that are otherwise not observed in non-resonant scattering. The appearance of 1st and 2nd order phonon modes is unambiguously observed in a broad range of temperatures from 5 to 320 K. The spectrum includes the Raman-active modes, i.e. E_{text {1g}}^{2}(Gamma) and A_{text {1g}}(Gamma) along with their Davydov-split counterparts, i.e. E_{text {1u}}(Gamma) and B_{text {1u}}(Gamma). The temperature evolution of the Raman scattering spectrum brings forward key observations, as the integrated intensity profiles of different phonon modes show diverse trends. The Raman-active A_{text {1g}}(Gamma) mode, which dominates the Raman scattering spectrum at T = 5 K quenches with increasing temperature. Surprisingly, at room temperature the B_{text {1u}}(Gamma) mode, which is infrared-active in the bilayer, is substantially stronger than its nominally Raman-active A_{text {1g}}(Gamma) counterpart.