One issue that has driven many of the experiments on high‐temperature superconductivity is the nature of the wavefunction of the electron pairs that carry the supercurrent (seePHYSICS TODAY, May 1993, page 17). For conventional superconductors, this wavefunction is isotropic, having an angular momentuml = 0,that is, s‐wave. But for the anisotropic copper‐oxide materials that exhibit critical temperatures above 40 K, the wave‐function may not be so simple.