Study of Dispersive Raman Modes inCu2O by Resonant Raman Scattering

We have observed shifts in energy of a number of Raman modes of ${\mathrm{Cu}}_2$O as a function of incident photon energy. We explain such energy shifts as due to dispersion in the phonons involved and obtain quantitative agreement between theory and experiment. From our data we have also determined the effective mass of the $1s$ yellow exciton in ${\mathrm{Cu}}_2$O to be $(3.0\mathrm{}\pm 0.2)m_0$.