Symmetry of Two- and Four- Electron States in Solids. Application to   Unconventional Superconductors
  Group theoretical technique for construction of two-electron wavefunctions with zero total momentum in solids based on the Mackey theorem on symmetrized squares is developed. These states correspond to singlet and triplet Cooper pairs. The nodal structure of these states is investigated group theoretically and compared with experimental data for unconventional superconductors. It is shown that when the Mackey theorem is applied twice, the main four-electron states in solids can be constructed. Possible connection of these states with experimental data is discussed. 
V.G.Yarzhemsky