Diquark condensates and the magnetic field of pulsars

We study the consequences of superconducting quark cores in neutron stars for the magnetic fields of pulsars. We find that within recent nonperturbative approaches to the effective quark interaction the diquark condensate forms a superconductor of second kind whereas previously quark matter was considered as a first kind superconductor. In both cases the magnetic field which is generated in the surrounding hadronic shell of superfluid neutrons and superconducting protons can penetrate into the quark matter core since it is concentrated in proton vortex clusters where the field strength exceeds the critical value. Therefore the magnetic field will not be expelled from the superconducting quark core with the consequence that there is no decay of the magnetic fields of pulsars. Thus we conclude that the occurence of a superconducting quark matter core in pulsars does not contradict the observational data which indicate that magnetic fields of pulsars have life times larger than 107 years.