Semiconductors systems exhibiting excitonic properties are discussed in terms of their coherent response, which is
extracted using two-dimensional coherent spectroscopy. This control method allows for separation of quantum pathways
that comprise the optical response, such as interactions between excitons, their dephasing rates, the effects of many-body
interactions and the role of structure on the microscopic electronic environment. Additional controls, such as polarization
can be used to further distinguish biexcitons and suppress many-body interactions. These result are compared and
contrasted with those from a semiconductor microcavity where the excitons form polaritonic modes due to normal-mode
splitting. Rephrasing spectra map the detuning dependence of the exciton-polariton branches. Increasing the detuning
shifts all features to higher energy and the expected anti-crossing is observed. An isolated biexciton is seen only at
negative detuning, separated by a binding energy. For positive detuning, the spectral weight of the off-diagonal features
swap, as the lower polariton branch and biexciton come into resonance. This indicates that the off-diagonal features are
sensitive to the interactions of the exciton-polaritons and other resonances in the system.
|