Highly anisotropic spin transport in ultrathin black phosphorus

Abstract

In anisotropic crystals, the direction-dependent effective mass of carriers can have a profound impact on spin transport dynamics. The puckered crystal structure of black phosphorus (BP) leads to direction-dependent charge transport and optical response, suggesting that it is an ideal system for studying anisotropic spin transport. To this end, we fabricate and characterize high mobility encapsulated ultrathin BP-based spin-valves in four-terminal geometry. Our measurements show that in-plane spin-lifetimes are strongly gate tunable and exceed one nanosecond. Through high out-of-plane magnetic fields, we observe a five-fold enhancement in the out-of-plane spin signal case compared to in-plane and estimate a colossal spin lifetime anisotropy of ~ 6. This finding is further confirmed by Oblique Hanle measurements. Additionally, we estimate an in-plane spin-lifetime anisotropy ratio of up to 1.8. Our observation of strongly anisotropic spin transport along three orthogonal axes in this pristine material could be exploited to realize directionally tunable spin transport.

19 pages, 4 figures

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• Hexagonal boron nitride crystal growth in the Li3BN2-BN system
• Large spin signal and spin rectification in folded-bilayer graphene
• Giant Spin Transport Anisotropy in Magnetic Topological Insulators
• Theory of polarization-switchable electrical conductivity anisotropy in nonpolar semiconductors
• Impact of the out-of-plane conductivity on spin transport evaluation in a van der Waals material