Large spin relaxation anisotropy and valley-Zeeman spin-orbit coupling in WSe2 /graphene/ h -BN heterostructures

Abstract

Large spin-orbital proximity effects have been predicted in graphene interfaced with a transition metal dichalcogenide layer. Whereas clear evidence for an enhanced spin-orbit coupling has been found at large carrier densities, the type of spin-orbit coupling and its relaxation mechanism remained unknown. We show for the first time an increased spin-orbit coupling close to the charge neutrality point in graphene, where topological states are expected to appear. Single layer graphene encapsulated between the transition metal dichalcogenide WSe2 and hBN is found to exhibit exceptional quality with mobilities as high as 100 000 cm 2 V −1 s −1 . At the same time clear weak anti-localization indicates strong spin-orbit coupling and a large spin relaxation anisotropy due to the presence of a dominating symmetric spin-orbit coupling is found. Doping dependent measurements show that the spin relaxation of the in-plane spins is largely dominated by a valley-Zeeman spin-orbit coupling and that the intrinsic spin-orbit coupling plays a minor role in spin relaxation. The strong spin-valley coupling opens new possibilities in exploring spin and valley degree of freedom in graphene with the realization of new concepts in spin manipulation.

Induced spin-orbit coupling in twisted graphene–transition metal dichalcogenide heterobilayers: Twistronics meets spintronics

“…The measurements of a large anisotropy of the in-plane and out-ofplane spin-relaxation times 17,24 can be interpreted 28 as an indication that a valley-Zeeman type SOC is also in-duced and its magnitude is comparable to the Rashba type SOC. This is consistent with the data extracted from SdH oscillations 13 and a similar conclusion was also reached in a more recent WAL measurement 20 . These measurements usually employed either bulk or few-layer TMDC substrate.…”

“…These heterostructures can posses functionalities that the individual constituent layers may not have. In order to increase the SOC in graphene, one of the most actively pursued directions is to interface it with materials that have strong intrinsic SOC, such as transition metal dichalcogenides (TMDCs) [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] . TMDCs are expected to be good candidates for graphene spintronics for two reasons: i) it was shown that TMDC substrates do not degrade the mobility of graphene 23,26 , and ii) they host a strong intrinsic SOC of the order of 100 meV (10 meV) in their valence (conduction) band 27 and hence can potentially be suitable materials for proximity induced SOC.…”

“…TMDCs are expected to be good candidates for graphene spintronics for two reasons: i) it was shown that TMDC substrates do not degrade the mobility of graphene 23,26 , and ii) they host a strong intrinsic SOC of the order of 100 meV (10 meV) in their valence (conduction) band 27 and hence can potentially be suitable materials for proximity induced SOC. Indeed, the measurement of weak antilocalization (WAL) [12][13][14]16,[19][20][21] and the beating of Shubnikovde Haas oscillations (SdH) 13 proved that SOC is strongly enhanced in graphene/TMDC heterostructures. Details regarding the type and magnitude of the proximity induced SOC are less clear.…”

Microscopic theory of spin relaxation anisotropy in graphene with proximity-induced spin-orbit coupling

“…This thrust has been fueled by the prospect of enhancing spin-orbital effects in graphene [7,8], while preserving the quintessential Dirac character of its 2D quasiparticles. The much sought after interface-induced SOC has been recently demonstrated in graphene/TMD bilayer heterostructures [9][10][11][12][13][14], where sharp weak antilocalization features in the magnetoconductance data [11][12][13][14] and dramatic reduction of spin lifetimes [15][16][17] hint at a massive enhancement of spinorbit interactions in the 2D carbon layer (up to 10 meV), consistent with the predictions of model calculations and first-principles studies [10,18,19].…”

Probing magnetism via spin dynamics in graphene/2D-ferromagnet heterostructures

“…With respect to graphene/TMDC heterostructures, this approach has proven to be highly successful: measurements of weak antilocalization (WAL) indicate enhanced SOC in the graphene layer [6][7][8][9][10][11][12]; spin switches have been realized based on spin absorption in the TMDC layer [13,14]; predictions of giant spin relaxation anisotropy [15], which may be useful for orientation-dependent spin filtering, have been subsequently confirmed by experiments [16,17]; and recent measurements have indicated sizable charge-tospin conversion in the graphene layer [18,19]. Giant spin lifetime anisotropy has also been predicted in graphene/TI heterostructures [20], and recent measurements of spin transport and WAL have suggested that TIs also induce strong SOC in graphene [21,22].…”