Structure of the Order Parameter of Topological Superconductors Based on 3d and 4d Transition Metal Oxides

Abstract

We consider experimental data on the order parameter structure in superconductors with a layered perovskite structure: La₂CuO₄ and Sr₂RuO₄. Experimental data are analyzed using the space group approach to two-electron states in crystals. From the crystalline symmetry of Sr₂RuO₄, we derive two-electron functions with E_u symmetry, having nodal planes consistent with experimental data. In the case of La₂CuO₄ and high-T_c materials, the order parameter corresponds to the irreducible representation B_1g with hidden symmetry D_4h. It is also shown that the charge density waves found in pseudogap states of high-T_c materials can be thought of as two-electron states of equivalent electrons with a nonzero momentum.