Bistability in the Tunnelling Current through a Ring of $N$ Coupled Quantum Dots

TL;DR

This paper investigates bistability in electron tunneling through a ring of coupled quantum dots with localized and delocalized orbitals, revealing size-dependent bistable current behavior using nonequilibrium Green functions.

Contribution

It introduces a detailed model of quantum dot rings with two orbitals per dot and demonstrates size-dependent bistability in tunneling current using advanced Green function techniques.

Findings

Bistability appears when the number of dots exceeds 50.

The effect becomes significant around 100 dots.

Mean-field approaches overestimate the bistability.

Abstract

We study bistability in the electron transport through a ring of N coupled quantum dots with two orbitals in each dot. One orbital is localized (called b orbital) and coupling of the b orbitals in any two dots is negligible; the other is delocalized in the plane of the ring (called d orbital), due to coupling of the d orbitals in the neighboring dots, as described by a tight-binding model. The d orbitals thereby form a band with finite width. The b and d orbitals are connected to the source and drain electrodes with a voltage bias V, allowing the electron tunnelling. Tunnelling current is calculated by using a nonequilibrium Green function method recently developed to treat nanostructures with multiple energy levels. We find a bistable effect in the tunnelling current as a function of bias V, when the size N>50; this effect scales with the size N and becomes sizable at N~100. The temperature effect on bistability is also discussed. In comparison, mean-field treatment tends to overestimate the bistable effect.