Friday, May 4, 2012
3:00pm (110 INSCC)
Title: Many-Body and Spin-Orbit Aspects of the AC Phenomena
The thesis reports on research in the general field of light interaction with matter. According to the topics addressed it can be naturally divided into two parts: (Part I) many-body aspects of the Rabi oscillations which a two-level systems undergoes under a strong resonant drive, and (Part II) absorption of the ac field between the spectrum branches of two-dimensional fermions that are split by the combined action of Zeeman and spin-orbit (SO) fields.
The focus of Part I are the following many-body effects that modify the conventional Rabi oscillations: (i) coupling of a two-level system to a single vibrational mode of the environment, and (ii) correlated Rabi oscillations in two electron-hole systems coupled by tunneling with strong electron-hole attraction. In (i) a new effect of Rabi-vibronic resonance is uncovered. If the frequency of the Rabi oscillations, ΩR is close to the frequency, ω0, of the vibrational mode, the oscillations acquire a collective character. It is demonstrated that the actual frequency of the collective oscillations exhibits a bistable behavior as a function of ΩR-ω0. The main finding in (ii) is, that the Fourier spectrum of the Rabi oscillations in two coupled electron-hole systems undergoes a strong transformation with increasing ΩR. For ΩR smaller than the tunneling frequency the spectrum is dominated by a low-frequency (<<ΩR ) component and contains two additional weaker lines; conventional Rabi oscillations are restored only as ΩR exceeds the electron-hole attraction strength.
The highlight of Part II is a finding that, while the spectrum of absorption between either Zeeman-split branches or SO-split branches is close to a δ-peak, in the presence of both, it transforms into a broad line with singular behavior at the edges. In particular, when two splitting are equal, absorption of very low (much smaller than the splitting) frequencies become possible. The shape of the absorption spectrum is highly anisotropic with respect to the exciting field. This peculiar behavior of the absorption is also studied in wire geometry, where the interplay between two couplings (Zeeman and spin-orbit splitting) affects the shape of numerous absorption peaks.