| dc.description.abstract | Nonlinear light-matter interaction plays a key role in the understanding, probing, and ultimately controlling light and matter. In particular, materials with strong nonlinear optical responses are highly desirable for many scientific disciplines and technological applications e.g. ultrafast nonlinear optics, nonlinear biosensing and imaging, efficient generation of entangled photon pairs for quantum computing and quantum sensing, and all-optical transistor and computer. This thesis focuses on the theoretical study and fundamental understanding of nonlinear light-matter interaction using group theory and first-principles electronic structure theory. The developed theoretical framework can also be used for the discovery and design of nonlinear optical materials.
Chapter I of this dissertation discusses the general background and concepts of nonlinear light matter interactions and the motivation of this study. Chapter II provides a general microscopic theory of various nonlinear responses of materials as well as symmetry principles that govern the fundamental nonlinear responses. In addition, density matrix formalism and Floquet theory as well as tight-binding method will be discussed. Chapter III will present the discovery of 2D multiferroic and topological materials.
Chapter IV, V, and VI will discuss several types of nonlinear light-matter interaction in different materials including semiconductors and metals as well as topological materials. Chapter IV focuses on the large second harmonic generation in two-dimensional materials, including first-principles density functional theory approach and the corresponding microscopic mechanisms of second harmonic generation in the low-dimensional materials. Chapter V focuses on the shift photocurrent and circular photocurrent in ferroelectric semiconductors. Such photocurrent is distinct from conventional linear photocurrent as they exhibit nonreciprocal behavior whose current flow direction can be controlled by ferroelectric polarization. Chapter VI focuses on the theory of ferroelectric nonlinear anomalous Hall effect in semimetals and topological materials, and a theoretical prediction of even-odd layer oscillation of ferroelectric nonlinear anomalous Hall effect in few-layer topological semimetals is discussed.
Chapter VII elaborates future directions and important issues to be addressed. In particular, other types of nonlinear light matter interactions are discussed, including surface second harmonic generation, inverse Faraday effect, nonlinear magnetophotocurrent in topological materials etc. In addition to the seconder-order effects, higher order effects will be also discussed, including third-harmonic generation, two-photon absorption, etc. The results presented demonstrate that the fundamental understanding of the nonlinear optical phenomena together with their symmetry principles may offer unprecedented opportunities for the discovery and design of nonlinear optical materials and enable novel devices such as nonlinear quantum electronics, spintronics, magnetoelectronics, and dynamic quantum materials which may foster the second quantum evolution. | en |
