the common building blocks for most high temperature (high tc) superconductors are copper oxide layers, as depicted in the figure. assume the distance between copper atoms (filled circles) as a. for simplicity let us also assume that in the 3rd dimensions these cuo2 layers are simply stacked with spacing c, and there are no other atoms in the crystal. in first approximation the layers have a four-fold symmetry; the crystal is tetragonal.
