Vortices and type-I superconductivity in neutron stars
  In a recent paper by Link, it was pointed out that the the standard picture of the neutron star core, composed of a mixture of a neutron superfluid and a proton type-II superconductor, is inconsistent with observations of long period precession in isolated pulsars. In the following we will show that intervortex force between the magnetic flux tubes may be attractive resulting in a type-I (rather than type-II) superconductor. In this case the magnetic field cannot exist in the form of magnetic flux tubes, supporting Link's observation. This behavior of the system is due to the strong interaction between the proton-neutron Cooper pairs, which was previously ignored. We also calculate the critical magnetic fields H_c and H_c2 for type-I/II superconductors. These results also support our claim of type-I superconductivity in the cores of neutron stars. 
Kirk B. W. Buckley, Max A. Metlitski, and Ariel R. Zhitnitsky   (University of British Columbia)