Group Theoretical Lines of Nodes in Triplet Chiral Superconductor Sr2RuO4

Abstract

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 D4h 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 Eu, 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 Eu symmetry are possible. This means that there are no so called symmetry protected lines of nodes on vertical planes for chiral Eu 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.