The Condensed Matter & Surface Sciences Colloquium series presents Dr. Fanyao Qu, of the University of Texas at Austina and the University of Brasilia, on “Strain Induced Topological Phase Transition in Graphen Nonoribbons and Excitonic Effects on Optical Spectra of Monolayer MoS2” on Thursday, April 3, at 4:10 p.m. in Walter 245.
Abstract: Strain has a significant effect on the electronic, quantum transport and optical properties of a material. A combination of basic elements of uniaxial strain, SOC, exchange field, and staggered potential leads to a very exotic physics. In the first part of my talk, I am going to show how to use these quantities to realize the topological phase transition between the chiral edge state and the pseudoquantum spin Hall state in graphen nonoribbons.
The Coulomb interaction between the electron and hole is exceptionally strong in MoS2 due to their heavy masses and the 2D confinement. The screened Coulomb interaction between electrons and holes, and the exchange interaction “mixes” different single-particle excitations, from valence band states to conduction band states, giving rise to modified transition energies. In the second part of my talk, I will report calculations, based on multi-band tight-binding model and Bethe-Sopeter equation, of electron-hole interaction effects on the optical spectra of monolayer MoS2. Excitonic effects qualitatively alter the optical spectra of monolayer MoS2. The intravalley Coulomb interaction preserves the valley coherence, while electron–hole exchange interaction causes valley decoherence.
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