© Los Alamos National Laboratory.
Left: In conventional superconductivity, the vibration of the metal's structural lattice provides a symmetrical attraction (fuzzy blue region) between two electrons. In this artist's conception, a passing electron causes the positively charged ions (gray) to pull together, which attracts a second electron that has its magnetic pole pointing in the opposite direction.
Right: In heavy-electron superconductors, electron pairing is caused by a purely electronic mechanism, their near approach to antiferromagnetic behavior. The localized electron spins shown here are close to being antiferromagnetic, being almost aligned in a configuration in which their spins alternate in direction from one lattice site to the next. A passing conduction electron induces a spin fluctuation that leads to spatially varying mix of both repulsive and attractive (the blue and yellow shading) forces on a second conduction electron that has its spin pointing in a direction opposite to that of the first. This pattern of alternating repulsion (at the origin) and attraction (at, for example, the four nearest neighbor sites) gives rise to a superconducting order parameter that has nodes (zeroes) where the repulsion is strongest and is maximum where the attraction is strongest. (Unit: 8)