Spin-polarized transport in quadruple quantum dots attached to ferromagnetic leads

TL;DR

This paper investigates spin-resolved transport in a quadruple quantum dot system connected to ferromagnetic leads, aiming to identify signatures of Nagaoka ferromagnetism through conductance and spin polarization measurements.

Contribution

It introduces a theoretical analysis of Nagaoka ferromagnetism in a quadruple quantum dot setup by examining transport properties under different Coulomb interaction conditions.

Findings

Sign change in current spin polarization indicates Nagaoka ferromagnetic order.

Transport coefficients vary with intra-dot Coulomb interactions.

Potential experimental signatures of Nagaoka ferromagnetism in quantum dots.

Abstract

Motivated by the experimental evidence of the Nagaoka ferromagnetism in quantum dot systems by Dehollain et al [1], we search for possible confirmation of such kind of ferromagnetism by analyzing the spin-resolved transport properties of a quadruple quantum dot system focusing on the linear response regime. In particular, we consider four quantum dots arranged in a two-by-two square lattice, coupled to external ferromagnetic source and drain electrodes. Turning on and off the specific conditions for the Nagaoka ferromagnetism to occur by changing the value of the intra-dot Coulomb interactions, we determine the transport coefficients, including the linear conductance, tunnel magnetoresistance and current spin polarization. We show that a sign change of the current spin polarization may be an indication of a ferromagnetic order of Nagaoka type which develops in the system.