Tunable magnetoresistance in an asymmetrically coupled single molecule junction

TL;DR

This paper demonstrates highly sensitive, voltage-tunable magnetoresistance in a single molecule junction caused by negative differential resistance, with potential applications in molecular spintronics and magnetic sensing.

Contribution

It reveals how asymmetric electrode coupling influences molecular transport and enables magnetic field sensitivity far exceeding Zeeman shifts in single-molecule devices.

Findings

Magnetoresistance shifts two orders of magnitude larger than Zeeman energy.

Voltage-tunable magnetoresistance can be controlled via bias.

Asymmetric coupling enhances the apparent voltage shift.

Abstract

Phenomena that are highly sensitive to magnetic fields can be exploited in sensors and non-volatile memories. The scaling of such phenomena down to the single molecule level may enable novel spintronic devices. Here we report magnetoresistance in a single molecule junction arising from negative differential resistance that shifts in a magnetic field at a rate two orders of magnitude larger than Zeeman shifts. This sensitivity to the magnetic field produces two voltage-tunable forms of magnetoresistance, which can be selected via the applied bias. The negative differential resistance is caused by transient charging of an iron phthalocyanine (FePc) molecule on a single layer of copper nitride (Cu2N) on a Cu(001) surface, and occurs at voltages corresponding to the alignment of sharp resonances in the filled and empty molecular states with the Cu(001) Fermi energy. An asymmetric voltage-divider effect enhances the apparent voltage shift of the negative differential resistance with magnetic field, which inherently is on the scale of the Zeeman energy. These results illustrate the impact that asymmetric coupling to metallic electrodes can have on transport through molecules, and highlight how this coupling can be used to develop molecular spintronic applications.