Full characterization of a carbon nanotube parallel double quantum dot

TL;DR

This study thoroughly characterizes a parallel double quantum dot system in a carbon nanotube, revealing strong coupling and similar properties of the dots, with implications for understanding multi-shell or bundled CNT structures.

Contribution

First detailed measurement and analysis of a parallel CNT double quantum dot with strong inter-dot coupling and characterization of its transport properties.

Findings

Identification of two quantum dots in parallel within a single CNT device.

Observation of strong, periodic anti-crossings indicating similar dot characteristics.

Extraction of coupling parameters and insights into the quantum dot formation in CNTs.

Abstract

We have measured the differential conductance of a parallel carbon nanotube (CNT) double quantum dot (DQD) with strong inter-dot capacitance and inter-dot tunnel coupling. Nominally, the device consists of a single CNT with two contacts. However, we identify two sets of Coulomb blockade (CB) diamonds that do not block transport individually, which suggest that two quantum dots (QDs) are contacted in parallel. We find strong and periodic anti-crossings in the gate and bias dependence, which are only possible if the QDs have similar characteristics. We discuss qualitatively the level spectrum and the involved transport processes in this device and extract the DQD coupling parameters. These results lead us to believe that clean and undoped QDs are formed parallel to the CNT axis, possibly on the outer and inner shells of a multi-wall CNT, or in a double-stranded CNT bundle.