  In most studies on all-optical diodes spatial asymmetry has been by necessity
applied to break Lorentz reciprocity. Here we suggest a paradigm for optically
induced nonreciprocity in semiconductor wires which are spatially
asymmetry-free and provide a very simple and efficient platform for plasmonic
devices. An azimuthal magnetic field induced by a plasmonic pump in the
semiconductor wire alters the material parameters and thus results in a
cross-nonlinear modulation of the plasmonic signal. Peculiarly the nonlinear
wavenumber shift has opposite signs for forward and backward signals whereas
Kerr or Kerr-like nonlinearity does not break Lorentz reciprocity in spatially
symmetric structures. This principle may open an avenue towards highly
integrated all-optical nonreciprocal devices.
