This phenomenon is slightly suppressed by a persistent current in the Little-Parks effect. The Josephson effect occurs when two materials with this property (10[1])are placed close together (10[1])with a barrier between them. A copper sulfide impurity may explain why (-5[1])LK99 unexpectedly displays (10[1])this phenomenon. (10[2]-5[1])which has also been observed in YBCO. (10[2])Phonon-electron interactions allow the formation of Cooper pairs in the BCS theory of this phenomenon. Materials displaying this phenomenon expel their magnetic field in the Meissner effect, which allows some trains to levitate. (10[1])For 10 points, name this low temperature phenomenon in which the resistance of a material drops to zero. ■END■ (10[1])