Electrical spin injection, transport, and detection in graphene-hexagonal boron nitride van der Waals heterostructures: progress and perspectives

TL;DR

This paper reviews recent advances in graphene spintronics using hexagonal boron nitride (hBN) as a substrate, encapsulation layer, and tunnel barrier, highlighting progress in spin injection, detection, and device performance.

Contribution

It provides a comprehensive overview of how hBN has improved spin transport and injection in graphene devices, including recent developments with crystalline hBN tunnel barriers.

Findings

hBN improves spin lifetime and injection efficiency in graphene

Crystalline hBN tunnel barriers enable room-temperature spin measurements

Bias-induced spin polarization observed with hBN barriers

Abstract

The current research in graphene spintronics strives for achieving a long spin lifetime, and efficient spin injection and detection in graphene. In this article, we review how hexagonal boron nitride (hBN) has evolved as a crucial substrate, as an encapsulation layer, and as a tunnel barrier for manipulation and control of spin lifetimes and spin injection/detection polarizations in graphene spin valve devices. First, we give an overview of the challenges due to conventional SiO$_2$ substrate for spin transport in graphene followed by the progress made in hBN based graphene heterostructures. Then we discuss in detail the shortcomings and developments in using conventional oxide tunnel barriers for spin injection into graphene followed by introducing the recent advancements in using the crystalline single/bi/tri-layer hBN tunnel barriers for an improved spin injection and detection which also can facilitate two-terminal spin valve and Hanle measurements, at room temperature, and are of technological importance. A special case of bias induced spin polarization of contacts with exfoliated and chemical vapour deposition (CVD) grown hBN tunnel barriers is also discussed. Further, we give our perspectives on utilizing graphene-hBN heterostructures for future developments in graphene spintronics.