Spin Hall angle in single-layer graphene

We investigate the spin Hall effect in a single-layer graphene device with disorder and interface-induced spin-orbit coupling. Our graphene device is connected to four semi-infinite leads that are embedded in a {Landauer-B\"uttiker} setup for quantum transport. We show that the spin Hall angle of graphene devices exhibits mesoscopic fluctuations that are similar to metal devices. Furthermore, the product between the {maximum spin Hall angle deviation} and dimensionless longitudinal conductivity follows a universal relationship $\Theta_{sH} \times \sigma = 0.18$. Finally, we compare the universal relation with recent experimental data and numerically exact real-space simulations from the tight-binding model.