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

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 SiO2 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.

Two-Dimensional Flexible High Diffusive Spin Circuits

“…This extraordinary ability, stemming from its low spinorbit coupling 6 and a negligible hyperfine interaction, brought a colossal drive for true planar multiterminal spin circuits that are promising for enabling novel technologies beyond the conventional twoterminal magnetoresistance applications. Over the past decade, graphene spintronics has witnessed significant developments [7][8][9] . These include the initial demonstration of micrometer scale lateral spin transport 10 , promising efficient spin transport 11 , improved ferromagnetic interfaces with graphene 12 for efficient spin injection, higher quality graphene channels via complex encapsulated structures 8,[13][14][15] , dry transfer methods 16,17 , and suspended schemes 18,19 .…”

“…Over the past decade, graphene spintronics has witnessed significant developments [7][8][9] . These include the initial demonstration of micrometer scale lateral spin transport 10 , promising efficient spin transport 11 , improved ferromagnetic interfaces with graphene 12 for efficient spin injection, higher quality graphene channels via complex encapsulated structures 8,[13][14][15] , dry transfer methods 16,17 , and suspended schemes 18,19 . Developments also include spin relaxation studies 9,[20][21][22] , more recent anisotropic effects 23,24 , observation of long-distance spin transport 4,5 , novel enhancements 25,26 , inversion effects using 2D insulators [27][28][29][30] as barriers for spin injection and innovative demonstrations 31,32 .…”

Large spin-relaxation anisotropy in bilayer-graphene/ WS2 heterostructures

“…The electron-spin degree of freedom and its interaction with other properties such as valley pseudospins in the presence of SOC provide access to spintronic phenomena such as spin-valley coupling [4][5][6][7]9], spin-Hall effect [10,11], (inverse) Rashba-Edelstein effect [12][13][14][15][16] and even topologically protected spin-states [17][18][19][20][21] which are not possible to realize in pristine graphene. The mentioned effects are sought after for realizing enhancement and electric field control of SOC [1,4,8,[22][23][24][25], efficient charge-current to spincurrent conversion and vice versa [10,[27][28][29], which will be the building blocks for developing novel spintronic applications [13,30].…”

Energy dissipation in van der Waals 2D devices

“…While vdW heterostructures composed of graphene, h-BN, BP and various transition metal dichalcogenides have shown tremendous potential for electronic [117], optoelectronic [118] (a) (b) (c) (d) and spintronic [119] applications, understanding how hot electrons generated by high electric field and incident laser dissipate energy is important and can lead to the development of energy-efficient electronic and ultrafast optoelectronic devices based on physics unique to vdW heterostructures. Here, we discuss how the unique carrier scattering dynamics in graphene-based vdW heterostructures can be exploited for optoelectronic applications in light emission and photodetection.…”