Spin-valley blockade in carbon nanotube double quantum dots

TL;DR

This paper theoretically investigates spin-valley blockade in carbon nanotube double quantum dots, considering effects like spin-orbit coupling and disorder, and explains experimental observations of current behavior under magnetic fields.

Contribution

It introduces a comprehensive model accounting for spin, valley, spin-orbit interaction, and disorder effects, revealing how disorder lifts blockade and influences current in nanotube quantum dots.

Findings

Disorder induces valley-Zeeman fields that lift the blockade.

Strong spin-orbit interaction leads to a zero-field dip in current.

The width of the dip depends on interdot tunneling amplitude.

Abstract

We present a theoretical study of the Pauli or spin-valley blockade for double quantum dots in semiconducting carbon nanotubes. In our model we take into account the following characteristic features of carbon nanotubes: (i) fourfold (spin and valley) degeneracy of the quantum dot levels, (ii) the intrinsic spin-orbit interaction which is enhanced by the tube curvature, and (iii) valley-mixing due to short-range disorder, i.e., substitutional atoms, adatoms, etc. We find that the spin-valley blockade can be lifted in the presence of short-range disorder, which induces two independent random (in magnitude and direction) valley-Zeeman-fields in the two dots, and hence acts similarly to hyperfine interaction in conventional semiconductor quantum dots. In the case of strong spin-orbit interaction, we identify a parameter regime where the current as the function of an applied axial magnetic field shows a zero-field dip with a width controlled by the interdot tunneling amplitude, in agreement with recent experiments.