Condensed Matter Seminar: "Exciton Bose-Einstein condensation and superfluidity in two-dimensional nanomaterials"

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 graphene, phosphorene, and transition metal dichalcogenide (TMDC) heterostructures. Indirect excitons are the Coulomb-bound pairs of electrons and holes confined to different parallel monolayers of a layered planar nanomaterial structure. It has been shown that the indirect excitons in gapped bilayer graphene can form BEC and experience superfluidity. 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. 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. Also analyzed are the effects of high magnetic fields on the BEC and superfluidity of exciton polaritons formed by the direct excitons in gapped monolayer graphene embedded in an optical microcavity to show that the polariton BEC can be manipulated by an external magnetic field, whereas the superfluid behavior can be controlled by changing the graphene gap. These results open up new avenues for the experimental realization of the exciton BEC and superfluidity phenomena as well as their practical applications in optoelectronics.