Quasi-two-dimensional fluctuations in the magnetization of La1.9Ca1.1Cu2

Abstract

We report the results of magnetization measurements with the magnetic field applied along the c-axis on superconducting La 1.9 Ca 1.1 Cu 2 O 6+δ single crystals processed under ultra high oxygen pressure. Strong fluctuation effects were found in both low and high field regimes. Scaling analysis of the high field magnetization data near the critical temperature (T c = 53.5 K) region reveals the characteristics of critical fluctuation behavior of quasi-two-dimensional (2D) superconductivity, described by Ginzburg-Landau theory using the Lowest Landau Level approximation. Low field magnetic susceptibility data can be successfully explained by the Lawrence-Doniach model for a quasi-2D superconductor, from which we obtained the ab plane Ginzburg-Landau coherence length of this system, ξ ab (0) = 11.8 ± 0.9 Å. The coherence length along the c-axis, ξ c (0), is estimated to be about 1.65Å, which is in-between those of 2D cuprate systems, such as Bi 2 Sr 2 Ca 2 Cu 3 O 10 and Bi 2 Sr 2 CaCu 2 O 8 , and quasi-3D cuprate systems, such as overdoped La 2-x Sr x CuO 4 and YBa 2 Cu 3 O 7-δ. Our studies suggest a strong interplay among the fluctuation effects, dimensionalities, and the ratios of the interlayer Cu-O plane spacing, s, to the c-axis coherence lengths. A high s/ξ c (0) was observed in the high pressure oxygenated La 1.9 Ca 1.1 Cu 2 O 6+δ , and that apparently drives this system to behave more like a quasi-2D superconductor.

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

“…It is important to avoid confusing H irr with the loss of superconducting correlations. As shown in a study of 0 10 20 30 the reversible magnetization on a similar sample of La-Ca-2126 with x = 0.1 [27], the temperature of the onset of diamagnetism shows very little change with fields up to 5 T, which is relatively close to what we observe for H irr when the field is parallel to the bilayers. To gain further insight into the behavior when the field is perpendicular, we turn to the measurements of transport anisotropy.…”

“…Evidence for the compositional uniformity of the superconducting phase in the annealed samples is given by the sharp superconducting transitions (width ∼ 5 K). A linear extrapolation of the transition region yields a magnetically-determined superconducting transition temperature T m c = 54 K for both compositions, slightly higher [24] than previously reported singlecrystal results [21,[25][26][27]. For the zero-field-cooling (ZFC) curves, 100% volume shielding would correspond to χ = 0.0126 emu g −1 Oe −1 ; the observed response is of this magnitude despite the fact that the volume fraction of the La-Ca-2126 phase is just 70% [20].…”

“…For comparison, magnetization measurements on a La-Ca-2126 crystal with x = 0.1 previously grown and annealed by our group had a similar T m c of 53.5 K, but also showed a small enhancement of the diamagnetic response below 13 K [21,27]. That contribution might be due to La-214 layers, which are also present in the current samples; however, no low-temperature jumps in the diamagnetism are apparent in Fig.…”

“…We note that there is a substantial range of temperature and field in which the bilayers appear to be superconducting while there is no coherent superconducting transport between bilayers. Analysis of the magnetization in the reversible range near the onset of diamagnetism found evidence of 2D scaling behavior [27]. Our results indicate that this is not just a matter of strong anisotropy in a 3D system, but that superconductivity actually develops within bilayers before Josephson coupling can provide 3D coherence.…”

Gapless spin excitations in superconducting La2−xCa1+xCu2O6 with Schneeloch1, Zhong2, Stone3 et al. 2019Phys. Rev. B5130View full textAdd to dashboardCite

“…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.…”