Growth and structural characterization of large superconducting crystals of La2−xCa1+xCu2O6<

Abstract

Large crystals of La2−xCa1+xCu2O6 (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, Tc, 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 La2CuO4, and an antiferromagnetic La8Cu8O20 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.

Evidence for magnetic-field-induced decoupling of superconducting bilayers in La2−xCa1+xCu2O6Zhong1, Schneeloch2, Chi3 et al. 2018Phys. Rev. BSelf Cite141120View full textAdd to dashboardCite

“…Crystals of La-Ca-2126 with x = 0.10 and 0.15 were grown by the travelling-solvent floating zone method [23]. The as-grown crystals were not superconducting, but they were converted to bulk superconductors by highpressure annealing in a gas of 20% O 2 / 80% Ar [20]. Transmission electron microscopy (TEM) on an early version of such an annealed crystal demonstrated the presence of thin intergrowths of La 2−x Ca x CuO 4 (La-214) [21].…”

“…Interpretation of the results requires some care, as the high-pressure oxygen annealing essential to achieving superconductivity also results in the presence of minority phases of La 2−x Ca x CuO 4 and La 8 Cu 8 O 20 . The latter compound is an antiferromagnetic insulator, while the former occurs as very thin intergrowths; all phases are crystallographically aligned along the c axis [20,21]. We believe that the segregation of these phases enhances the Ca concentration of the main La-Ca-2126 phase, thus providing sufficient hole doping to yield superconductivity.…”

“…In this paper, we investigate another cuprate system. We have recently succeeded in preparing superconduct-ing crystals of La 2−x Ca 1+x Cu 2 O 6 (La-Ca-2126) of sufficient size for inelastic neutron scattering experiments [20]. Here we present a study of the anisotropic transport and magnetic susceptibility for two of these samples.…”

Gapless spin excitations in superconducting La2−xCa1+xCu2O6 with Schneeloch1, Zhong2, Stone3 et al. 2019Phys. Rev. BSelf Cite5130View full textAdd to dashboardCite

“…In this paper, we present an inelastic neutron scattering study of La 2−x Ca 1+x Cu 2 O 6 single crystals, two of which exhibit bulk superconductivity induced by highpressure oxygen annealing. We have previously characterized the structures of these crystals [10,31]. The annealing appears to enhance the Ca concentration of the La-2126 phase into the superconducting regime, at the cost of creating some effective intergrowths of two other cuprate phases, as we explain below.…”

“…Synthesis of large, superconducting La-2126 crystals is difficult, as substitution of Ca or Sr for La at sufficient levels to yield superconductivity requires annealing in a high-pressure oxygen-containing atmosphere [7,8], and such facilities are relatively uncommon. We have recently succeeded in growing and oxygen-annealing large crystals of Ca-doped La-2126, achieving superconducting transition temperatures, T c , as high as 55 K [9][10][11]. In contrast to La-214, the La-2126 structure contains CuO 2 bilayers.…”