Observation of a coherent exciton-LO phonon resonance in a ZnSe single quantum well

A new coherent signal has been observed while performing two- beam degenerate four-wave mixing (FWM) experiments on a 3nm ZnMgSSe/ZnSe single quantum well (SQW) using 30fs laser pulses. In this SQW structure the exciton binding energy exceeds the LO-phonon energy (31.6 meV). The observed spectral feature is blue shifted with respect to the heavy-hole bound exciton transition by $\sim $32 meV and indicates the formation of a coherent exciton-LO phonon resonance with a dephasing time of $\sim $500 fs. This tentative assignment is further supported by photoluminescence excitation (PLE) and by reflection measurements. This work is supported by the National Science Foundation (DMR-0305076).