Growth and structural characterization of large superconducting crystals of La${}_{2-x}$Ca${}_{1+x}$Cu${}_2$O${}_6$

Abstract

Large crystals of La${}_{2-x}$Ca${}_{1+x}$Cu${}_2$O${}_6$ (La-Ca-2126) with $x=0.10$ and 0.15 have been grown and converted to bulk superconductors by high-pressure oxygen annealing. The superconducting transition temperature, $T_c$, is as high as 55~K; this can be raised to 60~K by post-annealing in air. Here we present structural and magnetic characterizations of these crystals using neutron scattering and muon spin rotation techniques. While the as-grown, non-superconducting crystals are single phase, we find that the superconducting crystals contain 3 phases forming coherent domains stacked along the $c$ axis: the dominant La-Ca-2126 phase, very thin (1.5 unit-cell) intergrowths of La${}_2$CuO${}_4$, and an antiferromagnetic La${}_8$Cu${}_8$O${}_{20}$ phase. We propose that the formation and segregation of the latter phases increases the Ca concentration of the La-Ca-2126, thus providing the hole-doping that supports superconductivity.

9 pages, 8 figures, version accepted in PRMaterials

Cited by in corpus (1)

• Gapless spin excitations in superconducting La${}_{2-x}$Ca${}_{1+x}$Cu${}_2$O${}_6$ with $T_c$ up to 55 K