'Levitation' of paramagnetic oxygen molecules over the surface of high temperature superconductors

The low temperature adsorption of molecular oxygen on a superconducting Y-Ba-Cu-O ceramic differs dramatically from the case of ordinary physical adsorption since it depends critically upon the electronic state of the adsorbent. When the adsorbent is in the superconducting state at 77 K, the amount of oxygen adsorbed is six times less than one for the adsorbent in the non-superconducting state at 94 K. The phenomenon also depends upon the external magnetic field. The abnormal oxygen adsorption on the superconductor seems to relate to the intrinsic paramagnetism of oxygen molecules, which can repulse from those regions of the adsorbent where the surface is absolutely diamagnetic.