Shot Noise of Charge and Spin Current of a Quantum Dot Coupled to Semiconductor Electrodes

TL;DR

This paper investigates charge and spin current fluctuations in a quantum dot coupled to semiconductor electrodes, revealing the importance of auto- and cross-shot noise in characterizing spin current fluctuations under magnetic fields.

Contribution

It introduces a detailed analysis of shot noise in charge and spin currents in quantum dots with semiconductor contacts, highlighting the role of magnetic fields and junction types.

Findings

Auto- and cross-shot noise are crucial for spin current fluctuation characterization.

Cross-shot noise of spin current is negative across all surface states in AS/QD/AS junctions.

In AB/QD/AB junctions, the cross-shot noise oscillates between positive and negative with gate voltage.

Abstract

Based on the scattering matrix theory and non-equilibrium green function method, we have investigated the fluctuations of charge and spin current of the systems which consists of a quantum dot (QD) with a resonant level coupled to two semiconductor contacts within in alternative site $(AS)$ and alternative bond $(AB)$ framework, where two transverse $(B_x)$ and longitudinal $(B_z)$ magnetic fields are applied to the QD. It is only necessary to use the auto-correlation function to characterize the fluctuations of charge current for a two-terminal system because of the relation which is defined as $\sum_{\alpha}^e S_{\alpha\beta}$ = $\sum_{\beta}^e S_{\alpha\beta}=0$. Our result shows that both auto-shot noise $(S_{LL})$ and cross-shot noise $(S_{LR})$ are essential to characterize the fluctuations of spin current when $B_x$ is present. Moreover, our model calculations show that the sign of the cross-shot noise of spin current is negative for all surface states of AS/QD/AS junctions, while it oscillates between positive and negative values for two surface states of AB/QD/AB junctions as we sweep the gate voltage.