  A stochastic nonlinear electrical characteristic of graphene is reported.
Abrupt current changes are observed from voltage sweeps between the source and
drain with an on/off ratio up to 10^(3). It is found that graphene channel
experience the topological change. Active radicals in an uneven graphene
channel cause local changes of electrostatic potential. Simulation results
based on the self-trapped electron and hole mechanism account well for the
experimental data. Our findings illustrate an important issue of reliable
electron transports and help for the understanding of transport properties in
graphene devices.
