Spin-Current and Spin-Splitting in Helicoidal Molecules Due to Spin-Orbit Coupling.

R A Caetano

doi:10.1038/srep23452

Abstract

The use of organic materials in spintronic devices has been seriously considered after recent experimental works have shown unexpected spin-dependent electrical properties. The basis for the confection of any spintronic device is ability of selecting the appropriated spin polarization. In this direction, DNA has been pointed out as a potential candidate for spin selection due to the spin-orbit coupling originating from the electric field generated by accumulated electrical charges along the helix. Here, we demonstrate that spin-orbit coupling is the minimum ingredient necessary to promote a spatial spin separation and the generation of spin-current. We show that the up and down spin components have different velocities that give rise to a spin-current. By using a simple situation where spin-orbit coupling is present, we provide qualitative justifications to our results that clearly point to helicoidal molecules as serious candidates to integrate spintronic devices.

Highlights

One of the main bottlenecks for the realization of spintronic devices is the difficulty in appropriately selecting electronic spin-polarization, without the need of an external magnetic field
We follow the time evolution of an initial unpolarized electronic wave packet moving in a helicoidal molecule, DNA as a representative example, and we show that, the spin-orbit coupling derived by Guo and Sun[19] does not lead to an unbalanced spin polarized current, it is enough to promote a spatial separation between the |↑ 〉 and |↓ 〉 spin components
This spatial separation of the spin components suggests that it is possible to use of helicoidal molecules as spin filters in spintronic devices

Summary

Introduction

One of the main bottlenecks for the realization of spintronic devices is the difficulty in appropriately selecting electronic spin-polarization, without the need of an external magnetic field. Gutierrez et al have formulated a quantum transport model which includes the spin-orbit coupling due to the presence of a helicoidal external electric field originated from charge accumulation along the helix[17,18] and a strongly spin-dependent current has been found. We follow the time evolution of an initial unpolarized electronic wave packet moving in a helicoidal molecule, DNA as a representative example, and we show that, the spin-orbit coupling derived by Guo and Sun[19] does not lead to an unbalanced spin polarized current, it is enough to promote a spatial separation between the |↑ 〉 and |↓ 〉 spin components. The central ingredient in order to have spin-orbit coupling is an electrostatic potential which, in the case of DNA molecules, is originated from accumulated charges along the helix[26]

Methods

Results

Conclusion