Highly anisotropic spin transport in ultrathin black phosphorus

TL;DR

This study demonstrates highly anisotropic spin transport in ultrathin black phosphorus, with gate-tunable in-plane spin lifetimes exceeding one nanosecond and a colossal out-of-plane spin lifetime anisotropy of about 6, revealing potential for directional spintronic devices.

Contribution

First experimental demonstration of strongly anisotropic spin transport in ultrathin black phosphorus with tunable spin lifetimes and high anisotropy ratios.

Findings

In-plane spin lifetimes exceed 1 nanosecond and are gate-tunable.

Out-of-plane spin signal shows five-fold enhancement under high magnetic fields.

Colossal spin lifetime anisotropy of approximately 6 observed.

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.