Spin transport in graphene nanostructures

TL;DR

This paper investigates spin injection and relaxation in nanostructured graphene, revealing that contact-induced relaxation dominates and proposing methods to improve spin relaxation measurements in graphene quantum dots.

Contribution

It provides the first detailed study of spin transport in graphene nanostructures smaller than the spin relaxation length, highlighting the impact of contact effects and edge processes.

Findings

Edge effects do not significantly affect spin relaxation in nanoislands.

Contact-induced relaxation has a major impact on spin transport.

High polarization contacts with low tunneling rates can improve measurements.

Abstract

Graphene is an interesting material for spintronics, showing long spin relaxation lengths even at room temperature. For future spintronic devices it is important to understand the behavior of the spins and the limitations for spin transport in structures where the dimensions are smaller than the spin relaxation length. However, the study of spin injection and transport in graphene nanostructures is highly unexplored. Here we study the spin injection and relaxation in nanostructured graphene with dimensions smaller than the spin relaxation length. For graphene nanoislands, where the edge length to area ratio is much higher than for standard devices, we show that enhanced spin-flip processes at the edges do not seem to play a major role in the spin relaxation. On the other hand, contact induced spin relaxation has a much more dramatic effect for these low dimensional structures. By studying the nonlocal spin transport through a graphene quantum dot we observe that the obtained values for spin relaxation are dominated by the connecting graphene islands and not by the quantum dot itself. Using a simple model we argue that future nonlocal Hanle precession measurements can obtain a more significant value for the spin relaxation time for the quantum dot by using high spin polarization contacts in combination with low tunneling rates.