Superfluidity of Dipolar Excitons in a Double Layer of α - T3 with a Mass Term

Oleg L Berman; Godfrey Gumbs; Gabriel P Martins; Paula Fekete

doi:10.3390/nano12091437

Superfluidity of Dipolar Excitons in a Double Layer of α - T₃ with a Mass Term

Nanomaterials (Basel). 2022 Apr 22;12(9):1437. doi: 10.3390/nano12091437.

Authors

Oleg L Berman^{1

2}, Godfrey Gumbs^{2

3

4}, Gabriel P Martins^{1

2

3}, Paula Fekete⁵

Affiliations

¹ Physics Department, New York City College of Technology, City University of New York, New York, NY 11201, USA.
² The Graduate School and University Center, City University of New York, New York, NY 10016, USA.
³ Department of Physics and Astronomy, Hunter College, City University of New York, New York, NY 10065, USA.
⁴ Donastia International Physics Center (DIPC), P de Manuel Lardizabal, 4, 20018 San Sebastian, Spain.
⁵ US Military Academy at West Point, 606 Thayer Road, West Point, NY 10996, USA.

Abstract

We predict Bose-Einstein condensation and superfluidity of dipolar excitons, formed by electron-hole pairs in spatially separated gapped hexagonal α-T3 (GHAT3) layers. In the α-T3 model, the AB-honeycomb lattice structure is supplemented with C atoms located at the centers of the hexagons in the lattice. We considered the α-T3 model in the presence of a mass term which opens a gap in the energy-dispersive spectrum. The gap opening mass term, caused by a weak magnetic field, plays the role of Zeeman splitting at low magnetic fields for this pseudospin-1 system. The band structure of GHAT3 monolayers leads to the formation of two distinct types of excitons in the GHAT3 double layer. We consider two types of dipolar excitons in double-layer GHAT3: (a) "A excitons", which are bound states of electrons in the conduction band (CB) and holes in the intermediate band (IB), and (b) "B excitons", which are bound states of electrons in the CB and holes in the valence band (VB). The binding energy of A and B dipolar excitons is calculated. For a two-component weakly interacting Bose gas of dipolar excitons in a GHAT3 double layer, we obtain the energy dispersion of collective excitations, the sound velocity, the superfluid density, and the mean-field critical temperature Tc for superfluidity.

Keywords: Bose-Einstein condensation; dipolar exitons; superfluidity.