Triply resonant second-order Raman scattering at the E0 and E00 gap of GaP under uniaxial stress

Using compressive uniaxial stress we have tuned the energy splitting between the spin-orbit-split and the light-hole valence band in GaP to be equal to the energy of two phonons (LO or TO). Thus, triply resonant second-order Raman scattering, where all three denominators involved in the Raman-scattering efficiency resonate simultaneously, becomes possible. We have observed the two-LO-, LO + TO-, and two-TO-phonon lines in triple-resonance conditions. We discuss the results in terms of Fröhlich and deformation-potential interaction.