Magnetism-induced Raman modes in two-dimensional CrI₃ atomic layers

We studied CrI₃ atomic layers down to the monolayer limit using temperature and magnetic field dependent micro-Raman spectroscopy. Two sets of Raman modes at frequencies of ~76 and ~125 cm^-1 are observed in CrI₃ atomic layers only in the antisymmetric channel below the magnetic phase transition temperature, suggesting that these two modes are related to the broken time reversal symmetry in the samples. By tracking the thickness dependence of both modes, we reveal that they are of the surface nature. Magnetic field dependent measurements of bilayer CrI₃ at 10 K further show that these modes disappear above the critical field of ~0.8 T. Possible origin of these two Raman modes is proposed.