24 \textmu m length spin relaxation length in boron nitride encapsulated bilayer graphene

TL;DR

This study demonstrates exceptionally long spin relaxation lengths up to 24 micrometers in boron nitride-encapsulated bilayer graphene at low temperatures, achieved through high mobility and optimized device design.

Contribution

The paper reports the first measurement of spin relaxation lengths up to 24 micrometers in bilayer graphene encapsulated in boron nitride, highlighting the impact of device length and encapsulation on spin transport.

Findings

Spin relaxation length reaches 24 μm at 4 K.

Spin relaxation time up to 2.9 ns.

Diffusion coefficient up to 0.52 m²/s at 4 K.

Abstract

We have performed spin and charge transport measurements in dual gated high mobility bilayer graphene encapsulated in hexagonal boron nitride. Our results show spin relaxation lengths $\lambda_s$ up to 13~\textmu m at room temperature with relaxation times $\tau_s$ of 2.5~ns. At 4~K, the diffusion coefficient rises up to 0.52~m$^2$/s, a value 5 times higher than the best achieved for graphene spin valves up to date. As a consequence, $\lambda_s$ rises up to 24~\textmu m with $\tau_s$ as high as 2.9~ns. We characterized 3 different samples and observed that the spin relaxation times increase with the device length. We explain our results using a model that accounts for the spin relaxation induced by the non-encapsulated outer regions.