d-wave superconductivity

[jeff]

Can anyone explain or give online references that give some explanation of what d-wave superconductivity is? My (poor) understanding of it is limited to the symmetry of the gap in the first brillouin zone is such that there are 4 nodes. But does that mean there are places where the gap is negative? And what does that even mean, to have a negative gap (energy must be invested to create a pair??) ?

[cregstephen]

it is similar to the LaTeX Code: d_{x^2-y^2} symmetry of an orbital angular momentum. So it isn't something mysterious.

What it does mean is that you get nodes along the diagonal directions. And no, you don't get negative gap, because the gap measurement (as in tunneling) only measure the absolute value. These measurements are not phase sensitive.
I will write back to you if I know any online references.