  Using an effective medium approach, we describe how by combining
mercury-cadmium-telluride semiconductor alloys with band gap energies of
opposite signs it may be possible to design a superlattice where the electrons
have isotropic zero-effective mass and a single valley linear energy-momentum
dispersion. We demonstrate that because of the zero-mass property, the
superlattice may have a strong nonlinear response under the action of an
external electromagnetic field.
