# Large spin-relaxation anisotropy in bilayer-graphene/WS$_2$ heterostructures

## TL;DR

This study demonstrates record spin lifetime anisotropy in bilayer-graphene/WS2 heterostructures, revealing strong spin-valley coupling and proximity-induced spin-orbit effects, with potential implications for spintronic devices.

## Contribution

It introduces a new measurement technique, Oblique Spin Valve, and provides detailed characterization of spin relaxation anisotropy in BLG/WS2 heterostructures, highlighting the role of SOC.

## Key findings

- Record spin lifetime anisotropy (~40-70) observed.
- High out-of-plane spin lifetime (~1-2 ns) measured.
- Low in-plane spin lifetime (~30 ps) indicating strong SOC.

## Abstract

We study spin-transport in bilayer-graphene (BLG), spin-orbit coupled to a tungsten di sulfide (WS$_2$) substrate, and measure a record spin lifetime anisotropy ~40-70, i.e. ratio between the out-of-plane $\tau_{\perp}$ and in-plane spin relaxation time $\tau_{||}$. We control the injection and detection of in-plane and out-of-plane spins via the shape-anisotropy of the ferromagnetic electrodes. We estimate $\tau_{\perp}$ ~ 1-2 ns via Hanle measurements at high perpendicular magnetic fields and via a new tool we develop: Oblique Spin Valve measurements. Using Hanle spin-precession experiments we find a low $\tau_{||}$ ~ 30 ps in the electron-doped regime which only weakly depends on the carrier density in the BLG and conductivity of the underlying WS$_2$, indicating proximity-induced spin-orbit coupling (SOC) in the BLG. Such high $\tau_{\perp}$ and spin lifetime anisotropy are clear signatures of strong spin-valley coupling for out-of-plane spins in BLG/WS$_2$ systems in the presence of SOC, and unlock the potential of BLG/transition metal dichalcogenide heterostructures for developing future spintronic applications.