Superpoissonian shot noise in organic magnetic tunnel junctions

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

Shot noise in magnetic tunneling structures with two-level quantum dots

“…Note that for β R = 1 the parallel and antiparallel configurations are equivalent (right electrode is then nonmagnetic). Then, when β R > 1, the Fano factor in the parallel configuration is lower while in the antiparallel state it is higher, which is in agreement with earlier observations [21]. In turn, dependence of the Fano factor on the parameters x R = R − R↑ /R + R↑ is shown in Fig.…”

“…More experimental data can be found in Ref. [21]. We have measured not only the shot noise and the corresponding Fano factor, but also the tunneling magnetoresistance (TMR).…”

“…In this paper we present a theoretical description of the model used for explanation of the experimental data on magnetic tunnel junctions with organic molecules [21]. Apart from charge fluctuations, we also consider spin fluctuations which influence the electric current.…”

“…Here we consider a similar problem of current and spin current noise in a magnetic tunnel junction with a nonmagnetic quantum dot, but the dot is attached to two ferromagnetic electrodes. The experiments on organic tunnel junctions with ferromagnetic contacts demonstrated super-Poissonian shot noise which additionally depends on magnetic polarization of the electrodes [21]. It was assumed that the model based on transfer of electrons through two discrete levels of molecules is sufficient to describe statistics of the fluctuations in such a system [21].…”

Noise Enhancement due to Telegraphic Switching in a Two-Level Quantum Dot Coupled to Spin-Polarized Leads

“…This phenomenon was later referred to as the dynamical channel blockade [2]. The super-Poissonian shot noise associated with this mechanism has been experimentally observed in organic magnetic tunnel junctions [3].…”