Coexistence of double-Q spin density wave and multi-Q pair density wave   in cuprate oxide superconductors
  Spatial 4a x 4a modulations, with a the lattice constant of CuO_2 planes, or the so called checkerboards can arise from double-Q spin density wave (SDW) with Q_1 = (pm pi/a, pm 3 pi/4a) and Q_2 = (pm 3 pi/4a, pm pi/a). When multi-Q pair density wave, that is, the condensation of d gamma-wave Cooper pairs with zero total momenta, pm 2Q_1, pm 2Q_2, pm 4Q_1, pm 4Q_2, and so on is induced by the SDW, gaps can have fine structures similar to those of the so called zero-temperature pseudogaps. 
Fusayoshi J. Ohkawa