Inelatic cotunneling current and shot noise of an interacting quantum dot with ferromagnetic correlations

TL;DR

This paper investigates inelastic cotunneling and shot noise in a strongly interacting quantum dot with ferromagnetic leads, revealing novel conductance anomalies and negative shot noise due to spin-flip processes.

Contribution

It introduces a microscopic Bloch-type equation approach to analyze spin relaxation, conductance, and shot noise in ferromagnetic quantum dots, highlighting new phenomena.

Findings

Zero-bias anomaly in differential conductance without magnetic field

Asymmetric peak splitting under magnetic field

Negative zero-frequency shot noise at low bias

Abstract

We explore inelastic cotunneling through a strongly Coulomb-blockaded quantum dot attached to two ferromagnetic leads in the weak coupling limit using a generic quantum Langevin equation approach. We first develop a Bloch-type equation microscopically to describe the cotunneling-induced spin relaxation dynamics, and then develop explicit analytical expressions for the local magnetization, current, and its fluctuations. On this basis, we predict a novel zero-bias anomaly of the differential conductance in the absence of a magnetic field for the anti-parallel configuration, and asymmetric peak splitting in a magnetic field. Also, for the same system with large polarization, we find a negative zero-frequency differential shot noise in the low positive bias-voltage region. All these effects are ascribed to rapid spin-reversal due to underlying spin-flip cotunneling.