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 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 black-phosphorus-based spin valves in a 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 fivefold 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.

在各向异性晶体中，载流子的方向相关有效质量会对自旋输运动力学产生深远的影响。黑磷的褶皱晶体结构导致方向依赖的电荷传输和光学响应，这表明它是研究各向异性自旋传输的理想系统。为此，我们制造并表征了四端几何形状的高迁移率封装超薄黑磷基自旋阀。我们的测量表明，面内自旋寿命具有很强的栅极可调性，并且超过一纳秒。通过高平面外磁场，我们观察到与平面内相比，平面外自旋信号情况增强了五倍，并估计了巨大的自旋寿命各向异性~ 6。这一发现得到了斜汉勒进一步证实测量。此外，我们估计面内自旋寿命各向异性比高达 1.8。我们对这种原始材料中沿三个正交轴的强各向异性自旋输运的观察可用于实现定向可调谐自旋输运。