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

TL;DR

This paper models the electronic states of ambipolar carbon nanotube quantum dots, analyzing spin-valley interactions, transition energies, and effects of nanotube bending, with implications for understanding Pauli blockade phenomena.

Contribution

It provides an atomistic tight-binding and configuration interaction analysis of charge states in carbon nanotube quantum dots, including effects of bending and magnetic fields.

Findings

Transition energies depend on magnetic field orientation.

Bending of nanotubes influences energy spectra.

Qualitative agreement with experimental data achieved.

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.