Dephasing of coherences betweenσ+andσ−exciton states in a ZnSe single quantum well

Abstract

We investigate interband coherences as well as coherences between δ + and δ - exciton states in a 10 nm thick ZnSe/ZnMgSe single quantum well by spectrally resolved three-pulse degenerate four-wave mixing using circularlypolarized 100 fs pulses. Polarization and intensity dependent measurements are performed to identify the coherent processes responsible for the nonlinear signal into the k 3 +k 2 -k 1 direction and to study the influence of Coulomb scattering on the dephasing rates. The experiments reveal nearly equal zero-density dephasing rates for coherences between δ + and δ - heavy- and/or light-hole exciton states as compared to the dephasing rate of the interband coherence between these states and the ground state. The measurements also demonstrate that exciton-exciton scattering destroys the phase coherence between heavy- and light-hole excitons about three times more effectively than the coherence between δ + and δ - heavy-hole excitons. The characteristic features of the experimental results are explained and reproduced by numerical calculations of the optical Bloch equations for a ten-level model including excitation induced dephasing.