EFFECT OF STACKING ON 2-DIMENSIONAL GAPLESS SUPERCONDUCTIVITY

We start from a two-dimensional superconductor (spin singlet) having nodal points in an energy gap function. The nature of the gap function is investigated in detail when the two-dimensional superconductors are stacked. The characteristic nodal points retain when an interlayer electron coupling (g2) is small compared to intralayer gapless BCS coupling (g1). We predict a novel superconducting phase below a certain temperature T(c)* when g2 increases to the same order with g1; as the temperature decreases from T(c), a superconducting state (HS phase) has nodes in a gap function down to T(c)* and subsequently a gap function with no zeros (LS phase) occurs below T(c)*.