Oleg L. Berman (CUNY)

May 3, 2019 @ 1:30 pm – 2:30 pm
Sasha Abanov2-8174E-mail

Superfluidity of excitons and polaritons in novel two-dimensional materials


This talk reviews the theoretical studies of the Bose-Einstein condensation (BEC) and superfluidity of indirect excitons and microcavity polaritons in quasi-two-dimensional (quasi-2D) van der Waals nanomaterials such as transition metal dichalcogenide (TMDC) heterostructures and phosphorene. Indirect excitons are the Coulomb-bound pairs of electrons and holes confined to different parallel monolayers of a layered planar nanomaterial structure. The high-T superfluidity of the two-component weakly-interacting Bose gas of the A-type and B-type indirect excitons in the TMDC heterostructures is proposed [1,2]. The critical temperature and superfluid velocity of the indirect excitons in a bilayer phosphorene nanostructure is shown to be anisotropic, dependent strongly on the particular direction of the exciton propagation [3]. The spin Hall effect for polaritons (SHEP) in a TMDC monolayer embedded in a microcavity is predicted [4]. It is demonstrated that two counterpropagating laser beams incident on a TMDC monolayer can deflect a superfluid polariton flow due to the generation the effective gauge vector and scalar potentials [4]. The polaritons cloud is formed due to the coupling of excitons created in a TMDC layer and microcavity photons. It was demonstrated that the polariton flows in the same valley are splitting: the superfluid components of the Aand Bpolariton flows propagate in opposite directionsalong the counterpropagating beams, while the normal components of the flows slightly deflect in opposite directionsand propagate almost perpendicularly to the beams [4]. The components of polariton conductivity tensor were obtained for polaritons without Bose-Einstein condensation (BEC) and in the presence of BEC and superfluidity [4]. The possible experimental observation of SHEP is discussed. These results open up new avenues for the experimental realization of the exciton and polariton BEC and superfluidity phenomena as well as their practical applications in optoelectronics [5].

[1] O. L. Berman and R. Ya. Kezerashvili, Phys. Rev. B 93, 245410 (2016)

[2] O. L. Berman and R. Ya. Kezerashvili, Phys. Rev. B 96, 094502 (2017). 

[3] O. L. Berman, G. Gumbs, and R. Ya. Kezerashvili, Phys. Rev. B 96, 014505 (2017).

[4] O. L. Berman, R. Ya. Kezerashvili, and Yu. E. Lozovik, Phys. Rev. B 99, 085438 (2019).

[5] D. W. Snoke and J. Keeling, Physics Today 70, 54 (2017).

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