Spin transport in two-layer-CVD-hBN/graphene/hBN heterostructures

Gurram, M. and Omar, S. and Zihlmann, S. and Makk, P. and Li, Q. C. and Zhang, Y. F. and Schönenberger, C. and van Wees, B. J. (2018) Spin transport in two-layer-CVD-hBN/graphene/hBN heterostructures. PHYSICAL REVIEW B, 97 (4). pp. 1-8. ISSN 2469-9950

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Abstract

We study room-temperature spin transport in graphene devices encapsulated between a layer-by-layer-stacked two-layer-thick chemical vapor deposition (CVD) grown hexagonal boron nitride (hBN) tunnel barrier, and a few-layer-thick exfoliated-hBN substrate. We find mobilities and spin-relaxation times comparable to that of SiO 2 substrate-based graphene devices, and we obtain a similar order of magnitude of spin relaxation rates for both the Elliott-Yafet and D'Yakonov-Perel' mechanisms. The behavior of ferromagnet/two-layer-CVD-hBN/graphene/hBN contacts ranges from transparent to tunneling due to inhomogeneities in the CVD-hBN barriers. Surprisingly, we find both positive and negative spin polarizations for high-resistance two-layer-CVD-hBN barrier contacts with respect to the low-resistance contacts. Furthermore, we find that the differential spin-injection polarization of the high-resistance contacts can be modulated by dc bias from − 0.3 to + 0.3 V with no change in its sign, while its magnitude increases at higher negative bias. These features point to the distinctive spin-injection nature of the two-layer-CVD-hBN compared to the bilayer-exfoliated-hBN tunnel barriers.

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