Negativity of the excess noise in a quantum wire capacitively coupled to a gate

TL;DR

This paper demonstrates that the excess noise in a quantum wire with capacitive coupling can be negative at zero temperature, challenging the typical expectation that noise always increases with voltage, and explores conditions for this phenomenon.

Contribution

It reveals conditions under which excess noise becomes negative in a quantum wire with capacitive coupling, including effects of frequency, transmission energy dependence, and capacitance regimes.

Findings

Negative excess noise can occur at zero temperature.

Negativity appears at finite frequency with energy-dependent transmission.

Voltage dependence of noise varies with capacitance and frequency regimes.

Abstract

The electrical current noise of a quantum wire is expected to increase with increasing applied voltage. We show that this intuition can be wrong. Specifically, we consider a single channel quantum wire with impurities and with a capacitive coupling to nearby metallic gates and find that its excess noise, defined as the change in the noise caused by the finite voltage, can be negative at zero temperature. This feature is present both for large ($c \gg c_q$) and small ($c \ll c_q$) capacitive coupling, where $c$ is the geometrical and $c_q$ the quantum capacitance of the wire. In particular, for $c \gg c_q$, negativity of the excess noise can occur at finite frequency when the transmission coefficients are energy dependent, i.e. in the presence of Fabry-P\'erot resonances or band curvature. In the opposite regime $c \lesssim c_q$, a non trivial voltage dependence of the noise arises even for energy independent transmission coefficients: at zero frequency the noise decreases with voltage as a power law when $c < c_q/3$, while, at finite frequency, regions of negative excess noise are present due to Andreev-type resonances.