DISCRIMINATION BETWEEN THE INTERBAND AND INTRABAND COHERENCES IN PUMP-PROBE SIGNALS FROM SEMICONDUCTORS

We discuss coherent heavy-hole light-hole quantum beats in transient D ump-probe signals from a homogeneous GaAs quantum well in tile low den sity regime using a microscopic density matrix theory. A key feature o f our theory is the inclusion of higher order correlation functions li ke the biexciton transition amplitude and the exciton density comprisi ng both interband and intraband character. Our calculations show that the heavy-hole light-hole quantum beats are: dominated by the longer l iving intraband coherent contributions for most excitation conditions. In the special case when both pump and probe are linearly polarized, forming: an angle of 45 degrees, the coherent signature is exclusively caused by the otherwise small contributions of the biexciton transiti on amplitude, i.e. an interband coherent correlation function. In this way the different interband and intraband dephasing times should be o bservable separately in PP signals, depending on the excitation condit ions.