7 April 2022 Thu 3 pm

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We firstly report on a peculiar propagation of bosons loaded by a short Laguerre-Gaussian pulse in a nearly flat band of a lattice potential. Taking a system of exciton-polaritons in a kagome lattice as an example, we show that an initially localized condensate propagates in a specific direction in space if anisotropy is taken into account. Secondly, we study the generation and annihilation of polariton vortex  excited by LG(Laguerre Gaussian) beam by solving Gross- Pitaevskii equation coupled with three different reservoirs. Exciton-polariton is quasiparticle arising from strong coupling between confined photon and exciton in semiconductor microcavity. By excitation with Laguerre Gaussian pump, exciton-polariton can generate vortex. We investigate how the polariton vortex behaves by changing pump duration and intensities. Lastly, we study optical transitions from impurity states to the conduction (and valence) band in two-dimensional Dirac materials, taking a monolayer of MoS2 as an example. We employ the model of a shallow impurity potential which localizes electrons described by a spinor wave function, and, first, find the system eigenstates taking into account the presence of two valleys in the Brillouin zone. Then, we find the spectrum of the absorbance (two-dimensional light absorption coefficient) and calculate the photoinduced electric current density due to the impurity-band transitions, drawing the general conclusions regarding the optical selection rules for the impurity-band optical transitions in gapped Dirac materials.

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