On superfluidity of indirect excitons in transition metals trichalcogenides van der Waals heterostructures

We study within a mean-field approach and the Bogoliubov approximation superfluidity of indirect excitons in transition metals trichalcogenides (TMTC) van der Waals heterostructures (vdWHs) composed from two TMTC monolayers separated by a varying number of hBN layers. We predict the angle-dependent superfluidity of indirect excitons in vdWHs that arise due to anisotropy of electron-hole masses. It is demonstrated that angle-dependent critical temperature Tc for superfluidity occurs beyond the sound-like approximation for the spectrum of collective excitation: for a given exciton density a maximum and minimum Tc of superfluidity is along chain and a-directions, respectively. In contrast to the anisotropic behavior of Tc for phosphorene [1], the vastly different angular dependence of Tc is observed for ZrS₃. In calculations, we used the Rytova-Keldysh (RK) and Coulomb potentials for charged carriers interaction to analyze the screening influence. For both potentials, the angle-dependent superfluidity of indirect excitons is observed. The critical temperature for the phase transition obtained using Coulomb potential is significantly larger than Tc calculated with RK potential. We suggest the experiment to observe the electron-hole superfluidity in a dilute weakly interacting gas of indirect excitons in TMTC vdWH.

[1] O. L. Berman, G. Gumbs, R. Ya. Kezerashvili, Phys. Rev. B 96, 014505, 2017.