Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)

Graduate Group


First Advisor

Andrew M. Rappe


Light-matter interaction, as the name suggested, describes the interaction between the illuminating light and different states of matters. In solid-state physics, people usually focus on how light influences the energetics and dynamics of materials where light is taken as a classical electromagnetic field. In the first part of this dissertation, we will focus on the situation where the frequency of light is lower than the band gaps of materials, so that the light will not be absorbed but scattered and possibly acquire a frequency shift, which is called Raman scattering. We will show how the conventional theory of Raman scattering developed for harmonic systems can be modified to treat highly anharmonic systems. The adapted theory will be used to reproduce the experimental Raman spectra of methylammonium lead iodide-a promising material for solar energy conversion-and demonstrate the atomistic origin of its strong lattice anharmonicity. Then, in the second part of this dissertation, we will shift our attention to the scenario where the photon energy surpasses the band gap and will be absorbed by the material. We will be mainly concerned with one specific phenomenon, the bulk photovoltaic effect (BPVE), which means that a steady DC current can be generated in spatially homogeneous but inversion-broken or time-reversal-broken materials. We will develop a theory for ballistic current, an important mechanism for BPVE in addition to shift current, and then use first-principles methods to evaluate it for real materials such as BaTiO3 and MoS2. Our theory and computation show clearly that the phonon ballistic current can be as important as shift current, while the exciton ballistic current is less appreciable. Moreover, we will investigate how BPVE will behave under a uniform magnetic field, demonstrating a sizable response of shift current at weak field and a nontrivial evolution of the spectral shape going into the strong field.


Available to all on Sunday, September 14, 2025

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