Quantum dots in carbon nanotubes

Abstract

In this overview paper, we present low-temperature electronic transport measurements of carbon nanotube quantum dots with a back gate. In a semiconducting tube, charge carriers could be completely depleted. The addition energy and the excitation spectrum have been studied as a function of the number of charges (electrons or holes), one by one. We observe electron-hole symmetry, which is a direct consequence of the symmetric band structure of the nanotube. The excitation spectrum for metallic nanotubes exhibits four-fold shell filling and is completely described by an extended constant-interaction model. Furthermore, nanotubes with a four-fold shell structure are investigated in a parallel magnetic field. The magnetic field induces a large splitting between the two orbital states of each shell, demonstrating their opposite magnetic moment and determining transitions in the spin and orbital configuration of the quantum dot ground state. Also, a small coupling is found between orbitals with opposite magnetic moments leading to anti-crossing behaviour at zero field. Current-voltage characteristics of suspended carbon nanotube quantum dots show an additional series of steps equally spaced in voltage. The energy scale of this harmonic, low-energy excitation spectrum is consistent with that of the longitudinal low-k phonon mode (stretching mode) in the nanotube. Finally, we report on a fully tunable carbon nanotube double quantum dot. We perform inelastic transport spectroscopy via the excited states in the double quantum dot, a necessary step towards the implementation of new microwave-based experiments for quantum information technology.

Strongly Coupled Nanotube Electromechanical Resonators

“…Owing to good electrical conductivity and lack of impurities and net nuclear spin, the electron charge and spin states in gate-defined CNT quantum dots (QDs) [4][5][6][7][8] are promising candidates for solid-state quantum information processing. However, a scalable quantum processor requires long-range couplings, which is a challenge for QDs, because there are only local interactions between neighboring QDs.…”

Correlation Effects and Spin Dependent Transport in Carbon Nanostructures

“…Such a dot is formed when electrons are conned to a small region within a carbon nanotube [7]. Experimentally it is accomplished by laying a CNT on a silicon dioxide surface, sitting on a doped silicon waver.…”

“…* corresponding author; e-mail: lipinski@ifmpan.poznan.pl When we connect a single nano-object to two magnetic electrodes, the spin dependent transport is predicted to interplay with single electron physics, i.e. with Coulomb blockade in the case of weak coupling [7] or with the Kondo eect in the case of stronger coupling between the nano-object and electrodes [8].…”

Ab Initio Analysis of a Quantum Dot Induced by a Local External Potential in a Semiconducting Carbon Nanotube

“…Numerous experimental efforts were devoted to fabrication and study of CNT-based quantum dots (CNTQD, see Ref. [2]), which were shown to work as single-electron transistors [3] or diodes. In many of these experiments metallic CNTs weakly coupled to the leads were used, where they showed characteristic features of the Coulomb blockade (CB).…”