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

The temperature evolution of the resonant Raman scattering from high-quality bilayer 2H-MoS2 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. E21g(Γ) and A1g(Γ) along with their Davydov-split counterparts, i.e. E1u(Γ) and B1u(Γ). 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 A1g(Γ) mode, which dominates the Raman scattering spectrum at T = 5 K quenches with increasing temperature. Surprisingly, at room temperature the B1u(Γ) mode, which is infrared-active in the bilayer, is substantially stronger than its nominally Raman-active A1g(Γ) counterpart.