Superfluidity of dipolar excitons in a black phosphorene double layer

The formation of dipolar excitons and their superfluidity in a black phosphorene double layer was studied [1]. It is predicted that a dilute weakly interacting Bose gas of dipolar excitons in a black phosphorene double layer exhibits superfluidity, caused by the dipole-dipole repulsion between dipolar excitons. In calculations the Keldysh and Coulomb potentials for the interaction between the electron and hole are employed to analyze the influence of the screening effects on the single-particle and collective properties of dipolar excitons. A critical velocity of superfluidity, spectrum of collective excitations, concentrations of the superfluid and normal components, and mean
field critical temperature for superfluidity are anisotropic and demonstrate the dependence on the direction of motion of dipolar excitons. The angular dependence of the critical temperature for superfluidity T_c(θ) for a phosphorene double layer for different exciton concentrations is calculated. It is shown that the critical temperature for superfluidity increases when the exciton concentration and the interlayer separation increase. The proposed experiment to observe a directional superfluidity of dipolar excitons is discussed.
[1] O.L. Berman, G. Gumbs, R.Ya. Kezerashvili, Phys, Rev. B 96, 014505 (2017).