Role of coherence in transport through engineered atomic spin devices

TL;DR

This paper develops a quantum master equation approach to describe the role of coherence in magnetic transport through atomic spin structures, capturing effects overlooked by classical rate equations.

Contribution

It introduces a Redfield-type master equation for atomic spin dynamics that incorporates quantum coherence and charge-specific states, improving the understanding of spin-dependent transport.

Findings

Coherence effects significantly influence spin-polarized tunneling currents.

The method accurately describes moderate lead-atom coupling regimes.

Quantum coherence must be considered for correct interpretation of transport measurements.

Abstract

We give a further step in the quantum mechanical description of engineered atomic spin structures by deriving a master equation of the Redfield type that governs the dynamics of the atomic spin density matrix. By generalizing this approach to charge-specific density matrices, we are able to describe magnetic transport quantities, such as the average inelastic current and the shot noise, accessible by tunneling spectroscopy. Our method suitably describes moderate lead-atom coupling regimes where quantum coherence effects cannot be disregarded. We contrast our approach with the existing descriptions in terms of rate equations and show examples where coherence effects are crucial to understand the physics of spin-polarized tunnel current through spin structures.