Abstract
Condensation of spatially indirect excitons, with the electrons and holes confined in two separate layers, has recently been observed in two different double layer heterostructures. High transition temperatures were reported in a double Transition Metal Dichalcogenide (TMD) monolayer system. We briefly review electron-hole double layer systems that have been proposed as candidates for this interesting phenomenon. We investigate the double TMD system WSe 2 /hBN/MoSe 2 , using a mean-field approach that includes multiband effects due to the spin-orbit coupling and self-consistent screening of the electron-hole Coulomb interaction. We demonstrate that the transition temperature observed in the double TMD monolayers, which is remarkably high relative to the other systems, is the result of (i) the large electron and hole effective masses in TMDs, (ii) the large TMD band gaps, and (iii) the presence of multiple superfluid condensates in the TMD system. The net effect is that the superfluidity is strong across a wide range of densities, which leads to high transition temperatures that extend as high as T B K T = 150 K.
Highlights
Indirect excitons are states of electrons and holes bound by their Coulomb attraction
In this paper we investigate the effects of multicomponent superfluidity in double Transition Metal Dichalcogenide (TMD) monolayers, and show that these effects contribute to the high transition temperatures observed in a TMD system
We present results for the specific system WSe2/hexagonal Boron Nitride (hBN)/MoSe2, with n-doped WSe2 and p-doped MoSe2, and draw general conclusions for the class of semiconductor TMDs
Summary
Indirect excitons are states of electrons and holes bound by their Coulomb attraction. In GaAs, the quantum wells are separated by a thin insulating barrier of AlxGa1−xAs which blocks recombination of the electrons and holes [4]. The strength of the electron-hole pairing is primarily controlled by the average effective separation between the electrons and the holes, determined by the thickness of the insulating barrier and by the widths of the quantum wells. Since the average effective separation is large, there is superfluidity only for densities 1010 cm−2. It would be interesting to observe superfluidity in this system, because it is likely to have a rich phase diagram of exotic superfluid phases [7] due to the large difference in electron and hole effective masses in GaAs
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