You need to use a custom plotter to plot Nedelec elements, as the dolfin.plot function interpolates any function to the mesh vertices. If you want to use an external plotter, I suggest you project/interpolate the solution to a suitable DG space, and use XDMFFile.write_checkpoint (see for instance Loading xdmf data back in - #4 by dokken) such that you can visualize it in Paraview.