Novel topological phase due to coexistence of superconductivity and spin-density wave: Application to high Tc superconductors

We consider a model of a coexistence phase between superconductivity(SC) and spin-density wave(SDW) where the SC is assumed to be of d x 2 − y 2 + id xy ( d 1 + id 2 ) symmetry and the SDW order parameter is of s-wave as well as d xy symmetry. The Hamiltonian having such a symmetry is shown to yield a novel topological coexistence phase in addition to the conventional one. It is shown that the amplitudes of both the order parameters determine a new phase diagram characterizing different topological phases. A possible experimental realization of such topological phases in a recent ARPES data of high T c superconductors in the extreme underdoped regime is analyzed by considering the effective order parameter to be a combination of d x 2 − y 2 SC and dxy SDW.