Positive and negative Coulomb drag in vertically integrated one-dimensional quantum wires

TL;DR

This paper reports the observation of both positive and negative Coulomb drag in closely spaced vertically integrated quantum wires, with detailed analysis of how electron subband occupancy influences the drag effect.

Contribution

It presents the first measurements of Coulomb drag between vertical quantum wires separated by only 15 nm, with independent control of electron densities and analysis of subband effects.

Findings

Positive drag can reach up to 25% in magnitude.

Drag sign depends on the relative subband occupancy of the wires.

Results support momentum-transfer and charge-fluctuation models.

Abstract

Electron interactions in and between wires become increasingly complex and important as circuits are scaled to nanometre sizes, or employ reduced-dimensional conductors like carbon nanotubes, nanowires and gated high mobility 2D electron systems. This is because the screening of the long-range Coulomb potential of individual carriers is weakened in these systems, which can lead to phenomenon such as Coulomb drag: a current in one wire induces a voltage in a second wire through Coulomb interactions alone. Previous experiments have observed electron drag in wires separated by a soft electrostatic barrier $\gtrsim$ 80 nm. Here, we measure both positive and negative drag between adjacent vertical quantum wires that are separated by $\sim$ 15 nm and have independent contacts, which allows their electron densities to be tuned independently. We map out the drag signal versus the number of electron subbands occupied in each wire, and interpret the results in terms of momentum-transfer and charge-fluctuation induced transport models. For wires of significantly different subband occupancies, the positive drag effect can be as large as 25%.