Superconducting phase with the (d + id) order parameter in an ensemble of Hubbard fermions on the triangular lattice

Abstract

In the framework of the t–J ₁–J ₂–V model, the integral equation determining the order parameter Δ(p) of the superconducting phase is derived for an ensemble of strongly correlated fermions on a triangular lattice using the diagram technique for the Hubbard operators. Taking into account the interaction between the Hubbard fermions within two coordination spheres, we demonstrate that the exact analytical solution Δ2(p) of this equation for the superconducting phase with the ($\left( {{d_{{x^2} - {y^2}}} + i{d_{xy}}} \right)$) symmetry can be expressed as a superposition of two chiral basis functions. This gives rise to a new set of nodal points for the complex parameter Δ2(p). Moreover, at some critical value x _c of the charge carrier density, we obtain a gapless phase with six Dirac points. The passing of x through x = x _c is accompanied by the topological quantum transition corresponding to the change in the topological parameter Q.