Low lying excitations of few electrons in quantum dots

[Excerpt from the Introduction]: This thesis focuses on neutral excitations of few-electrons states in nanofabricatedQDsmeasured by inelastic light scattering. The analysis of the spectra demonstrate that this technique can open a venue in the study of quasi-particles at the nanoscale. A model of electronic states confined in QDs is presented in the first chapter, while the second one provides a survey of the relevant experimental studies in this field. Special attention is paid to the process of inelastic light scattering by introducing a description of the selection rules for the scattering processes by electrons in semiconductor QDs. Chapter 3 describes the nano-fabrication techniques of doped AlGaAs/GaAs QDs and the different setups used for the measurements. Experiments performedwith μ-photoluminescence that demonstrate the confinement and the homogeneity of the fabricated QDs are reported at the end of this chapter. Chapter 4 reports inelastic light scattering spectra fromQDs with many electrons. In these experiments the atomic-like shell structure of the electronic states is demonstrated. The framework used to describe this regime of highly populated QDs is similar to the one used for transport experiments in the Coulomb blockade regime.Observations of tunneling excitations in coupled quantumdots with inelastic light scattering will also be presented. The most innovative results of this work are presented in chapter 5 that focuses on the study of interaction phenomena that take place in QDs in the few electron regime. The correlations that occur among the electrons deeply affect the inelastic light spectra in these systems. Themain outcome regards the case of QDs with four electrons where strong correlation effects have been found in the behavior of spin and charge collective excitations. Light scattering spectra from these dots at zero and finite perpendicularmagnetic fieldswill be presented. The evaluation of the excitation spectra as a function of the magnetic field reveals a ground-state transition between correlated states of the four electrons with different spin configurations.