The wavefunction which describes a Cooper pair of electrons in a superconductor is an exponential like the free particle wavefunction. In fact, all the Cooper pairs in a superconductor can be described by a single wavefunction in the absence of a current because all the pairs have the same phase - they are said to be "phase coherent" (Clarke). If two superconductors are separated by a thin insulating layer, then quantum mechanical tunneling can occur for the Cooper pairs without breaking up the pairs. Clarke envisions this condition as the wavefuntions for Cooper pairs on each side of the junction penetrating into the insulating region and "locking together" in phase. Under these conditions, a current will flow through the junction in the absence of an applied voltage (the DC Josephson effect).