Nodeless $s$-Wave Superconducting Phases in Cuprates with Ba$_2$CuO$_3$-Type Structure

Hidden, one-dimensional, strongly nested, and almost half-filled Fermi surface in Ba$_2$CuO$_{3+y}$ superconductors

“…The former hosts an overdoped, quasi 1D d b 2 −c 2 band, while the latter displays two-orbital, d x 2 −y 2 and d z 2 physics. Both compounds have been studied theoretically and several mechanisms for the superconductivity have already been proposed [6,8,28,31,36,37]. Let us stress, that a rigid bandstructure doping from either parent compound will always be plagued by the ambiguity of which structure is realized for the experimental Ba 2 CuO 3.2 compound, especially since both parent compounds are far away from the superconducting oxygen content.…”