Interactions and topology in two-dimensional semiconductor and semimetal
| dc.contributor.advisor | MacDonald, Allan H. | |
| dc.contributor.committeeMember | Chelikowsky, James R | |
| dc.contributor.committeeMember | Fiete, Gregory A | |
| dc.contributor.committeeMember | Register, Lenoard F | |
| dc.creator | Xue, Fei, 1990- | |
| dc.date.accessioned | 2018-10-01T20:08:32Z | |
| dc.date.available | 2018-10-01T20:08:32Z | |
| dc.date.created | 2018-08 | |
| dc.date.issued | 2018-09-14 | |
| dc.date.submitted | August 2018 | |
| dc.date.updated | 2018-10-01T20:08:33Z | |
| dc.description.abstract | This dissertation presents our study of interaction and topology effects in two-dimensional semiconductor and semimetal. In the first part, we explore the ground state thermodynamic phases in various systems using a mean-field theory including long-range Coulomb interaction. In particular, we have discovered two distinct phases with different number of exciton condensate flavors in a bilayer system of two-dimensional semiconductors with spin/valley degree of freedoms. The exciton condensate phase is characterized by spontaneous inter-layer phase coherence and counterflow superfluidity. We have also studied the phase diagram of a model quantum spin Hall system as a function of band inversion and band-coupling strength, demonstrating that when band hybridization is weak, an interaction-induced nematic insulator state emerges over a wide range of band inversion. We also develop a fully microscopic theory of equilibrium polariton condensates that treats the two-dimensional quantum well band states explicitly and goes beyond the commonly used model in which bare excitons are treated as Bose particles that are coupled via flip-flop interactions with cavity photons. In the second part, we present our study of collective excitations in an exciton condensate using a time-dependent mean-field theory. By constructing a fluctuation Lagrangian based on a variational wave-function capturing exciton density and phase fluctuations, we are able to get the collective mode spectra and demonstrate the stability of exciton condensate phase. Moreover, we apply a linear response theory to identify a number of collective modes with a strong electron-hole pairing amplitude(Higgs-like) component. Next, we generalize our time-dependent mean-field theory to finite temperature to address the long debate question that whether a CDW phase of a semimetal is due to Coulomb interaction or electron-phonon interaction. Our theory includes both intraband and interband excitations and direct and exchange interactions, and allows for the formation of exciton condensates at low temperatures. | |
| dc.description.department | Physics | |
| dc.format.mimetype | application/pdf | |
| dc.identifier | doi:10.15781/T2SB3XH72 | |
| dc.identifier.uri | http://hdl.handle.net/2152/68623 | |
| dc.language.iso | en | |
| dc.subject | Exciton | |
| dc.subject | Exciton condensate | |
| dc.subject | Quantum spin Hall insulator | |
| dc.subject | Nematic insulator | |
| dc.subject | Charge density wave | |
| dc.subject | Collective excitation | |
| dc.subject | Polariton | |
| dc.subject | Higgs mode | |
| dc.title | Interactions and topology in two-dimensional semiconductor and semimetal | |
| dc.type | Thesis | |
| dc.type.material | text | |
| thesis.degree.department | Physics | |
| thesis.degree.discipline | Physics | |
| thesis.degree.grantor | The University of Texas at Austin | |
| thesis.degree.level | Doctoral | |
| thesis.degree.name | Doctor of Philosophy |
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