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arXiv · 1712.00815

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

Mallikarjuna Gurram·Siddhartha Omar·Simon Zihlmann·Péter Makk·Qiucheng Li·Yanfeng Zhang·Christian Schönenberger·Bart J. van Wees
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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 vapour 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 obtain a similar order of magnitude of spin relaxation rates for both the Elliott-Yafet and D'Yakonov-Perel' mechanisms. The behaviour 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 V to +0.3 V with no change in its sign, while its magnitude increases at higher negative bias. These features mark a distinctive spin injection nature of the two-layer-CVD-hBN compared to the bilayer-exfoliated-hBN tunnel barriers.

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Mallikarjuna Gurram, Siddhartha Omar, Simon Zihlmann, Péter Makk, Qiucheng Li, Yanfeng Zhang, Christian Schönenberger, Bart J. van Wees. 2017-12-03. Spin transport in two-layer-CVD-hBN/graphene/hBN heterostructures. https://doi.org/10.1103/physrevb.97.045411

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