Charge rearrangement and screening in a quantum point contact

TL;DR

This study uses charge measurements to analyze screening and charge rearrangements in a quantum point contact, revealing deviations from classical models and highlighting the role of exchange interactions and density of states.

Contribution

It provides quantitative measurements of screening in a QPC and identifies the effects of exchange interactions and density of states on charge rearrangements.

Findings

Measured screening closely matches Thomas-Fermi-Poisson predictions

Deviations near mode openings indicate additional charge rearrangements

Exchange interactions significantly influence the first mode opening

Abstract

Compressibility measurements, sensitive to charge rearrangements, are performed on a quantum point contact (QPC). Screening due to mobile charges in the QPC is quantitatively measured, using a second point contact to detect the screened electrical potential. These measurements are performed from pinch-off through the opening of the first few modes in the QPC. While the measured signal closely matches a Thomas-Fermi-Poisson prediction, deviations from the classical behavior, in the form of additional dips, are apparent near the openings of the different modes, with the largest dip at the opening of the first mode. Density functional calculations attribute the first dip to exchange interactions. The other dips reflect the diverging density of states at the opening of each one-dimensional mode, which affects both kinetic and exchange contributions to the energy.