Conductance Anomaly and Fano Factor Reduction in Quantum Point Contacts

TL;DR

This study investigates how conductance anomalies in quantum point contacts affect shot noise and Fano factor, revealing a consistent link between conductance anomalies and asymmetric spin channel transmission.

Contribution

It demonstrates that conductance anomalies in QPCs are always associated with Fano factor reduction and asymmetric spin channel transmission, providing new insights into spin-dependent transport.

Findings

Anomaly at 0.5 G_0 correlates with up to 67% channel asymmetry.

Conductance anomalies always accompany Fano factor reduction.

Spin gap energy evolves with conductance increase.

Abstract

We report an experimental study on the shot noise as well as the dc transport properties of a quantum point contact (QPC) whose conductance anomaly can be tuned electrostatically by the gate electrodes. By controlling the single QPC so that it has no anomaly or an anomaly at $0.5 G_0$, $0.8 G_0$ or $0.9 G_0$ ($G_0 = 2e^2/h$), we prove that the anomaly always accompanies the Fano factor reduction due to the asymmetric transmission of the two spin-dependent channels for the conductance lower than $G_0$. For the QPC tuned to have the anomaly at $0.5 G_0$ the channel asymmetry is found to be as large as 67% with the spin gap energy gradually evolving as the conductance increases.