Group theoretical lines of nodes in triplet chiral superconductor Sr₂RuO₄

Cooper pair wavefunctions for chiral triplet (p-wave) superconductor Sr₂RuO₄ were considered making use of the spin-space group approach, and the states similar to A and B phases of ³He belonging to IRs (irreducible representations) of D_4h group are constructed making use of projection operator technique. Group theoretical lines of nodes were obtained for space-group analog of B phase. In this case nodal and nodeless one-dimensional states belong to the same IR, and differ by spin projection on vertical plane. Four chiral states, similar to A phase and belonging to complex IR E_u, are classified by the label of one-dimensional even IR. These states are non-unitary and differ by nodal structures and momentum projections on vertical axis. It was obtained that for each vertical plane of symmetry nodal and nodeless chiral states of E_u symmetry are possible. This means that there are no so called symmetry protected lines of nodes on vertical planes for chiral E_u states, but experimental vertical lines of nodes in Sr₂RuO₄ do not contradict with general group theoretical consideration. The results are in agreement with experimental nodal structure and may be used as alternative initial basis in microscopic and phenomenological theories of superconductivity in Sr₂RuO₄. (author)