Superpoissonian shot noise in organic magnetic tunnel junctions

TL;DR

This study reveals superpoissonian shot noise in organic magnetic tunnel junctions with PTCDA barriers, highlighting the role of interfaces and multilevel tunneling in electron transport.

Contribution

It demonstrates superpoissonian shot noise in organic junctions and introduces a model involving multilevel tunneling through interfacial bonds.

Findings

Fano factor exceeds 1.5-2 times the maximum for inorganic barriers.

Shot noise indicates spin-dependent electron bunching.

Interfaces significantly influence shot noise in organic tunneling.

Abstract

Organic molecules have recently revolutionized ways to create new spintronic devices. Despite intense studies, the statistics of tunneling electrons through organic barriers remains unclear. Here we investigate conductance and shot noise in magnetic tunnel junctions with PTCDA barriers a few nm thick. For junctions in the electron tunneling regime, with magnetoresistance ratios between 10 and 40\%, we observe superpoissonian shot noise. The Fano factor exceeds in 1.5-2 times the maximum values reported for magnetic tunnel junctions with inorganic barriers, indicating spin dependent bunching in tunneling. We explain our main findings in terms of a model which includes tunneling through a two level (or multilevel) system, originated from interfacial bonds of the PTCDA molecules. Our results suggest that interfaces play an important role in the control of shot noise when electrons tunnel through organic barriers.