Spectral narrowing of four-wave mixing signals for excitons in the layered semiconductor GaSe

The spectral narrowing has been observed using time-resolved and spectrally resolved four-wave mixing measurements on a layered semiconductor GaSe. The narrowing of four-wave mixing spectra is one of the evidences of the non-Markovian dephasing. From the calculation of the non-Markovian theory for exciton-phonon interaction, it has been found that the excitons in GaSe are confined to 7 layers and that the correlation time of the interaction is 1.1 ps, which defines the limit of the non-Markovian time regime.