Anomalous features of resonant hyper-Raman scattering in CuBr quantum dots: Evidence of exciton-phonon-coupled states similar to molecules

A resonant hyper-Raman scattering signal has been successfully observed in CuBr quantum dots of a weak-confinement regime. It is found that up to fifth-order LO-phonon scattering signals appear in a two-photon resonance with the lowest confined state of the $Z_{12}$, $S$ exciton, and that the observed order $N$ depends on the two-photon energy $2\hslash {\omega }_i$ for the excitation in such a way that it conforms to the equation $N<~\frac{(2\mathrm{}\hslash {\omega }_i-E_{\mathrm{edge}})}{\hslash {\omega }_{\mathrm{LO}}}$, with $\hslash {\omega }_{\mathrm{LO}}$ and $E_{\mathrm{edge}}$ being energies of the LO phonon and the absorption edge, respectively. The anomalous result observed indicates that coupled states of the Wannier exciton and the LO phonon are rather good elementary excitations in these dots.