Electronic structure of (1e,1h) states of carbon nanotube quantum dots

Abstract

We provide an atomistic tight-binding description of a few carriers confined in ambipolar (n-p) double quantum dots defined in a semiconducting carbon nanotube. We focus our attention on the charge state of the system in which Pauli blockade of the current flow is observed [F. Pei et al., Nat. Nanotechnol. 7, 630 (2012); E. A. Laird et al., ibid 8, 565 (2013)] with a single excess electron in the n-dot and a single hole in the p-dot. We use the configuration interaction approach to determine the spin-valley structure of the states near the neutrality point and discuss its consequences for the interdot exchange interaction, the degeneracy of the energy spectrum and the symmetry of the confined states. We calculate the transition energies lifting the Pauli blockade and analyze their dependence on the magnetic field vector. Furthermore, we introduce bending of the nanotube and demonstrate its influence on the transition energy spectra. The best qualitative agreement with the experimental data is observed for nanotubes deflected in the gated areas in which the carrier confinement is induced.

Spin-valley dynamics of electrically driven ambipolar carbon-nanotube quantum dots

“…12]. We have found [14] that the bends of the CNT appearing at the area where the confinement potential is defined on the gates results in energy spectra which qualitatively agree with the experimental spectrum of transitions lifting the Pauli spinvalley blockade of the current [12].…”

“…These states are referred to as "nonblocked" in the following. The nonblocked states enter into an avoided crossing that is opened at B = 0 by the exchange integral [14,41], hence their non-linear dependence on B near 0T. The orbital magnetic dipole moment due to the elec- Table II.…”

“…The lifting of the Pauli blockade in states B1 and B2 is achieved via transitions to one of the states N1 or N2 [11,12,14,15] -see the arrows in Fig. 5(a-c) that is induced by the ac electric field.…”

“…The energy spectrum of the (1e,1h) system was determined with the atomistic tight binding approach in Ref. [14]. The driven electron dynamics was discussed in Ref.…”

Double quantum dots defined in bilayer graphene

“…The wave functions obtained with the tight-binding approach are used in the configuration interaction method [35,36]. The atomistic approach when applied to the exact diagonalization method naturally accounts for the intervalley scattering induced by the short range component of the Coulomb interaction [38][39][40].…”