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Ion Sensors Using Diamond Field-effect Transistors
早稲田大学博士(工学)早大学位記番号:新9387doctoral thesi
Diagrammatic approach to excitonic effects on nonlinear optical response
Optical responses of atomically thin 2D materials are greatly influenced by
electron-hole interactions. It is by far established that exciton signatures
can be well-identified in the optical absorption spectrum of quasi-2D
materials. However, the same level of understanding of excitonic effects on
nonlinear optical responses and the ability to compute them accurately is still
much desired. Based on the functional integral formalisms and working in the
velocity gauge, we introduce a convenient Feynman diagram approach for
calculating nonlinear responses including excitonic effects. By dressing
electron-photon interactions with electron-hole ladder diagrams, we derive an
expression for second-order optical responses and provide a comprehensive
description of excitonic effects. We apply our approach to a monolayer h-BN
model and show qualitative changes in the second harmonic generation spectrum
when comparing with results assuming independent particles. Our approach can be
readily extended to higher order optical responses and is feasible for
first-principles calculations
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