The electron-hole superfluidity in two coaxial nanotubes

J. Brana, Srećko Kilić, Leandra Vranješ Markić

Виктор Павлович Маслов

Andreas Schmitt

Godfrey A. Gumbs, Yonatan Abranyos

The recent developments in the experimental realization of quasi-one-dimensional (1D) systems exhibit many interesting features. These include current quantization which has the potential application for a current standard as well as quantum information and security schemes. In this paper, we investigate the effect of spin-orbit interaction (SOI) on the energy levels of electrons confined to quantum dots on the surface of nanotubes. The radius of a nanotube is a few nanometers and is quasi-1D. The energy levels play a crucial role in determining the electron transport properties.The SOI may arise from the electrostatic confining potential due to gates applied perpendicular to the axis of the nanotube. The quantum computation scheme which we are suggesting consists of a nano-circuit of nanotubes on which electrons are confined within dots. The qubit operation is based on the exchange interaction between a pair of spins occupying states within the quantum dots. We employ a simple model for the electron confinement to obtain the energy eigenstates. Our simplified calculation was able to show that the SOI splits the energy levels which are then used to obtain the exchange energy of a pair of spins with the s-wave Heitler-London approach. We calculate the exchange energy of the entangled electrons on a pair of coaxial and parallel nanotubes as a function of separation between the nanotubes and show that the SOI enhances the entanglement.

J.-P. Gallinar

M. Zarenia, A. Perali, François Maria Peeters +1 more

We predict enhanced electron-hole superfluidity in two coupled electron-hole armchair-edge terminated graphene nanoribbons separated by a thin insulating barrier. In contrast to graphene monolayers, the multiple subbands of the nanoribbons are parabolic at low energy with a gap between the conduction and valence bands, and with lifted valley degeneracy. These properties make screening of the electron-hole interaction much weaker than for coupled electron-hole monolayers, thus boosting the pairing strength and enhancing the superfluid properties. The pairing strength is further boosted by the quasi one-dimensional quantum confinement of the carriers, as well as by the large density of states near the bottom of each subband. The latter magnifies superfluid shape resonances caused by the quantum confinement. Several superfluid partial condensates are present for finite-width nanoribbons with multiple subbands. We find that superfluidity is predominately in the strongly-coupled BEC and BCS-BEC crossover regimes, with large superfluid gaps up to 100 meV and beyond. When the gaps exceed the subband spacing, there is significant mixing of the subbands, a rounding of the shape resonances, and a resulting reduction in the one-dimensional nature of the system.