Non-equilibrium current and noise in inelastic tunneling through a magnetic atom

TL;DR

This paper explains nonmonotonic conductance and predicts super-Poissonian noise in inelastic tunneling through a magnetic atom, attributing these phenomena to nonequilibrium spin populations and anisotropic relaxation effects.

Contribution

It introduces a model that accounts for nonequilibrium spin populations and anisotropic relaxation, explaining experimental conductance features and noise characteristics.

Findings

Nonmonotonic differential conductance explained by nonequilibrium spin states.

Prediction of super-Poissonian current noise due to nonequilibrium effects.

Absence of certain nonequilibrium features explained by anisotropic relaxation.

Abstract

In a recent experiment, Hirjibehedin {\it et al.} [Science {\bf 317}, 1199 (2007)] performed inelastic tunneling spectroscopy of a single iron atom absorbed on a nonmagnetic substrate. The observed steps in the differential conductance marked the spin excitation energies. In this Letter, we explain observed nonmonotonicities in the differential conductance by a nonequilibrium population of the atom spin states. Furthermore, we predict super-Poissonian current noise due to this nonequilibrium situation. By introducing an anisotropic relaxation channel we are also able to explain the remarkable absence of nonequilibrium features at certain conductance steps.