Motivated by the success of the momentum average (MA) approximation for the single-polaron and bipolaron cases, in this thesis we pursue the first generalization of this technique to the case of weakly-doped insulators beyond the Migdal limit. In search of a suitable starting point, we investigate the ground states of a variety of model Hamiltonians, inspired by real materials such as the rare-earth nickelates, polyacetylene, barium bismuthates, and buckminsterfullerene.
The ground state of the 2D nickelate sheet is found to exhibit cuprate-like orbital polarization unimpeded by weak to moderate electron-phonon coupling, lending further support to the proposal for Ni 3d^7 like superconductivity in nickelate thin films and heterostructures. Investigating polyacetylene leads to the development of a semi-analytical technique that can be used to account for zero-point lattice energy in determining the equilibrium geometry of any crystal. The study of a simplified, one-dimensional model of buckminsterfullerene results in the first generalization of MA to a system with two polaron clouds, and a phonon-driven mechanism for exciton dissociation that could be responsible for photocurrent generation in these strongly polar materials.
Because both the nickelates and polyacetylene turn out to be too complex as starting points for MA generalization, we focus on a simplified, s-p chain model of the barium bismuthates. We ultimately succeed in generalizing MA for this band insulator -- the first application of its kind. We compare the results to those from determinant quantum Monte Carlo to establish the accuracy of the MA results, obtained at lower computational cost.
Finally, we share in the development of the first open-sourced Python package implementing automatic MA equation generation via the GGCE method, which allows MA-style methods to be easily used by non-experts -- and is expected to expand to provide access to more existing MA methods in the future.
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2023-06-12T10:00:002023-06-12T13:00:00Electron-phonon coupling in insulators beyond the Migdal limitEvent Information:
Motivated by the success of the momentum average (MA) approximation for the single-polaron and bipolaron cases, in this thesis we pursue the first generalization of this technique to the case of weakly-doped insulators beyond the Migdal limit. In search of a suitable starting point, we investigate the ground states of a variety of model Hamiltonians, inspired by real materials such as the rare-earth nickelates, polyacetylene, barium bismuthates, and buckminsterfullerene.
The ground state of the 2D nickelate sheet is found to exhibit cuprate-like orbital polarization unimpeded by weak to moderate electron-phonon coupling, lending further support to the proposal for Ni 3d^7 like superconductivity in nickelate thin films and heterostructures. Investigating polyacetylene leads to the development of a semi-analytical technique that can be used to account for zero-point lattice energy in determining the equilibrium geometry of any crystal. The study of a simplified, one-dimensional model of buckminsterfullerene results in the first generalization of MA to a system with two polaron clouds, and a phonon-driven mechanism for exciton dissociation that could be responsible for photocurrent generation in these strongly polar materials.
Because both the nickelates and polyacetylene turn out to be too complex as starting points for MA generalization, we focus on a simplified, s-p chain model of the barium bismuthates. We ultimately succeed in generalizing MA for this band insulator -- the first application of its kind. We compare the results to those from determinant quantum Monte Carlo to establish the accuracy of the MA results, obtained at lower computational cost.
Finally, we share in the development of the first open-sourced Python package implementing automatic MA equation generation via the GGCE method, which allows MA-style methods to be easily used by non-experts -- and is expected to expand to provide access to more existing MA methods in the future.Event Location:
https://ubc.zoom.us/j/61540621166?pwd=UGZDVkpiUTVmdEY5Qmtva2REVzVrQT09