2024 Theses Doctoral

Anharmonicity and Electron-Phonon Interactions in Periodic Systems

Shih, Petra

Anharmonic lattice dynamics and electron-phonon interactions are crucial to many intriguing physical phenomena in condensed matter physics. In my thesis, I develop theoretical methods and use them to characterize physical properties of model systems and realistic novel materials.

First, I introduce vibrational dynamical mean-field theory on models of anharmonic phonons using various impurity solvers, and describe the theoretical extensions to treat non-local interactions.

Second, I characterize phononic and excitonic ground state properties of the superatomic semiconductor, Re₆Se₈Cl₂, which exhibits quasi-ballistic exciton dynamics at room temperature. We attribute this behavior to the formation of polarons due to coupling with acoustic phonons and parameterize a Hamiltonian to study the ground state properties.

Finally, I introduce a method to calculate the Green’s function that characterizes the equilibrium dynamical properties of polarons. I demonstrate its performance on the Holstein model at finite temperature, and show its applications to systems with general coupling, electron-electron interaction, and anharmonicity.