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

Area of Science:

• Condensed Matter Physics
• Nanoscience
• Quantum Electronics

Background:

• Electron interactions are crucial in nanoscale circuits and reduced-dimensional conductors.
• Weakened screening of Coulomb potential in these systems leads to phenomena like Coulomb drag.
• Previous experiments showed Coulomb drag in wires separated by wider barriers (≳80 nm).

Purpose of the Study:

• To investigate Coulomb drag in closely spaced (∼15 nm) adjacent vertical quantum wires.
• To explore the influence of independently tunable electron densities on drag effects.
• To differentiate between momentum-transfer and charge-fluctuation transport models.

Main Methods:

• Fabrication of adjacent vertical quantum wires with independent electrical contacts.
• Measurement of Coulomb drag signals by varying electron densities and sub-band occupancies.
• Analysis of drag phenomena using both momentum-transfer and charge-fluctuation models.

Main Results:

• Observed both positive and negative Coulomb drag between quantum wires separated by ∼15 nm.
• Demonstrated that drag effects are dependent on the relative sub-band occupancies of the wires.
• Achieved a significant positive drag effect (up to 25%) for wires with disparate sub-band occupancies.

Conclusions:

• Coulomb drag in closely spaced quantum wires is sensitive to electron density and sub-band population.
• Both momentum transfer and charge fluctuation mechanisms contribute to observed drag effects.
• The study provides new insights into electron interactions in nanoscale electronic systems.