The role of asymmetry in formation of the superfluid state in electron–hole systems

• Two coaxial nanotubes with spatially separated carriers are considered.
• Mass and geometry asymmetry can adversely affect the pairing and superfluidity.
• These two asymmetries can effectively compensate each other to support superfluidity.

We consider a system of two coaxial nanotubes separated by a dielectric with the spatially separated electrons and holes confined on each nanotube. The pairing conditions in such systems are studied in the weak coupling limit. It is found that the electron–hole asymmetry caused by electron and hole mass difference and the difference in the radii of the nanotubes can adversely affect the pairing in the system. It is also found that under certain conditions these two asymmetries can effectively compensate each other, therefore significantly increasing the range of the system's parameters for which the superfluid state can exist.