Shot Noise in Magnetic Tunnel Junctions: Evidence for Sequential Tunneling

TL;DR

This paper reports the experimental detection of sub-Poissonian shot noise in magnetic tunnel junctions, highlighting the role of impurity-mediated sequential tunneling and its dependence on magnetic configuration.

Contribution

It provides the first experimental evidence of shot noise suppression in magnetic tunnel junctions due to impurity-assisted sequential tunneling.

Findings

Shot noise is sub-Poissonian in magnetic tunnel junctions.

Fano factor varies with magnetic alignment, being enhanced in antiparallel configuration.

A model of sequential tunneling through impurity levels explains the observations.

Abstract

We report the experimental observation of sub-Poissonian shot noise in single magnetic tunnel junctions, indicating the importance of tunneling via impurity levels inside the tunnel barrier. For junctions with weak zero-bias anomaly in conductance, the Fano factor (normalized shot noise) depends on the magnetic configuration being enhanced for antiparallel alignment of the ferromagnetic electrodes. We propose a model of sequential tunneling through nonmagnetic and paramagnetic impurity levels inside the tunnel barrier to qualitatively explain the observations.