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Title: Strong light-matter coupling in microcavity-embedded semiconductor quantum wells and quantum dots
Author: Sivalertporn, Kanchana
ISNI:       0000 0004 2738 7671
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2013
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This thesis presents a theoretical investigation of exciton polaritons in strongly-coupled exciton-photon microcavity systems. Two different systems, a coupled quantum well (CQW) embedded in a planar microcavity and a quantum dot (QD) inside a micropillar cavity, are studied using suitable theoretical models. The exciton-polariton states are calculated and their optical properties are investigated in detail, showing a good agreement with experimental observations. For a CQW structure, the excitonic states in the presence of the electric field applied in the growth direction are calculated by solving the Schrodinger equation in real space. The field dependence of exciton transition energy, binding energy, oscillator strength, lifetime and absorption is studied. The exciton ground state experiences a crossover from direct to indirect state at low electric field. A single state-basis calculation in which only the electron and hole ground states are taken into account is also made and compared with the full accurate calculation model. The polariton effect in a microcavity-embedded CQW is investigated based on the semiclassical theory. The light-matter interaction is treated by solving coupled material and Maxwell's equations. The reflectivity and absorption spectra are calculated for different detunings using the scattering matrix method. When a cavity mode is tuned to an exciton mode (zero detuning), an anticrossing of two polariton modes is observed, showing that the system is in the strong coupling regime. In addition, the fractions of direct exciton, indirect exciton and cavity modes contributed to the polariton states are calculated using the microscopic theory. The resulting polariton state with comparable contributions ofall three components called dipolariton is observed. Finally, the dynamics of the strongly-coupled exciton-cavity system in the QD-micropillar system is studied using the four wave mixing (FWM) theory applied to the Jaynes-Cummings model. Spectrally resolved and time-resolved FWM signals are calculated for different temperatures. Temperature plays the role of the parameter controlling the detuning. The beat periods of the first and second rungs of the JC ladder are also investigated, showing that the second rung has a sqaure- shorter period compared to the beat period of the first rung. To reveal the coherent coupling between two distant QDs, the FWM signals are Fourier-transformed into a two-dimensional frequency domain. It is found that the off-diagonal components in these 2D spectra are nonzero, demonstrating the coherent coupling between isolated QDs. In addition, the phase correction is developed. This procedure is neccessary for a comparison with the experiment which has random phases for different detunings. A quantitative agreement between the prediction and measurement is achieved and demonstrated.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics