Resonant Brillouin Scattering of Exciton Polaritons in 2H–PbI2

Resonant Brillouin scattering spectra are measured on a layer semiconductor 2H–PbI 2 . The observed exciton polariton dispersion in the direction parallel to the c -axis is interpreted by a two branch polariton model yielding the translational exciton mass of 2.3 m 0 and the effective dielectric constant of 10. The anisotropy of the effective mass is estimated to be m // / m ⊥ =3.4 for exciton and 4.4 for conduction electron, respectively.