High temperature superconducting granular balls

When a strong electric field is applied to a suspension of micron-sized hig h T-c superconducting particles in liquid nitrogen, the particles quickly a ggregate together to form balls. The millimeter-size balls hold over 10(6) particles each. They are sturdy, surviving constant heavy collisions with t he electrodes. The ball formation is a result of superconductivity, As the c-axis coherence length is shorter than the Thomas-Fermi screening length, the electric field produced by the charged surface layer turns off the coup ling between the interlayers. This loss of Josephson energy becomes a posit ive surface energy. Its minimization leads to the balls.