  We discuss the Overhauser effect (particle-hole pairing) versus the BCS
effect (particle-particle or hole-hole pairing) in QCD at large quark density.
In weak coupling and to leading logarithm accuracy, the pairing energies can be
estimated exactly. For a small number of colors, the BCS effect overtakes the
Overhauser effect, while for a large number of colors the opposite takes place,
in agreement with a recent renormalization group argument. In strong coupling
with large pairing energies, the Overhauser effect may be dominant for any
number of colors, suggesting that QCD may crystallize into an insulator at a
few times nuclear matter density, a situation reminiscent of dense Skyrmions.
The Overhauser effect is dominant in QCD in 1+1 dimensions, although
susceptible to quantum effects. It is sensitive to temperature in all
dimensions.
