Enhanced Gertsenshtein effect in type-II superconductors

Previously published calculations show that gravitational waves propagate inside superconductors with a phase velocity reduction of ∼300 times and a wavenumber increase of ∼300 times. This result has major significance for the propagation of gravitational waves. It is shown here that one important consequence may be regarded as a considerably enhanced Gertsenshtein effect for very-high-frequency gravitational waves within type-II superconductors. This arises because type-II superconductors do not always completely expel large magnetic fields; above their lower critical field they allow vortices of magnetic flux to channel the magnetic field through the material. Within these vortices, the superconducting order parameter reduces to zero and so the material has properties approaching those of normal material or non-superconductor. Varying the applied magnetic field varies the proportion of material that is normal, which consequently affects the propagation speed of very-high-frequency gravitational waves through a type-II superconductor.