Higgs Boson in Superconductors

Superfluid helium, describable by a two component order parameter, exhibits only the Bogolubov mode with energy 0 at long wavelengths, while aLorentz invariant theory with a two component order parameter exhibits a finite energy mode at long wavelengths (the Higgs boson), besides the above mass less mode. The mass less mode moves to high energies if it couples to electromagnetic fields (the Anderson Higgs mechanism). Superconductors, on the other hand have been theoretically and experimentally shown to exhibit both modes. This occurs because the excitations in superconductors have an (approximate) particle hole symmetry and therefore show a similarity to Lorentz invariant theories