▎ 摘　　要

In addition to the giant peak of the nonlocal resistance RNL, an anomalous negative value of RNL has been observed in graphene systems, although its formation mechanism is not quite understood yet. In this work, utilizing the nonequilibrium Green's function method, we calculate the local-current flow in an H-shaped noninteracting graphene system located in a ballistic regime. Similar to the previous conclusions obtained from viscous hydrodynamics, the numerical results show that a local-current vortex appears between the nonlocal measuring terminals, and it induces a backflow current and a remarkable negative voltage drop at the probe. Specifically, the stronger the vortex is, the more negative RNL becomes. In addition, spin-orbital coupling is added as an additional tool to study this exotic vortex, although this coupling is not a driving force for the arising vortex at all. Moreover, a breakdown of the nonlocal Wiedemann-Franz law is obtained in this ballistic system, and two experimental criteria are provided to confirm the existence of this exotic vortex. Notably, it is shown that the vortex actually originates from a collision between the flowing current and the boundaries, due to the long electron mean free path and the resulting ballistic transport caused by the specific linear spectrum of graphene.