Enhancement of rf breakdown field of superconductors by multilayer coating

It is shown that the rf breakdown magnetic field of superconducting resonator cavities can be significantly enhanced by multilayer coating consisting of alternating insulating layers and thin superconducting layers of thickness smaller than the London penetration depth. Such coating increases the field of vortex penetration and the quality factor determined by a small surface resistance Rs in the Meissner state. Delaying strong rf vortex dissipation up to fields higher than the thermodynamic critical field Bc of Nb makes it possible to take advantage of many type-II superconductors with higher Bc and lower Rs in high-field rf applications.