This phenomenon is slightly suppressed by a persistent current in the Little-Parks effect. The Josephson effect occurs when two materials (-5[1])with this property are placed close together with a barrier between them. A copper sulfide impurity may explain why LK99 unexpectedly (10[1])displays this phenomenon. which has also been observed in YBCO. Phonon-electron interactions allow the formation of Cooper pairs (10[1])in the BCS theory of this (10[1])phenomenon. Materials displaying this phenomenon expel their magnetic field in the Meissner effect, which allows some trains to levitate. For 10 points, name this (10[1])low temperature phenomenon in which the (10[1])resistance of a material (10[1])drops to zero. ■END■ (10[3])