engleski

17O NMR Study of High-Tc Cuprate (CaLa)(BaLa)CuO

We investigate the high temperature superconductor cuprate (CaxLa1-x)(Ba1.75-x La0.25+x)Cu3Oy(CLBLCO), with YBa2Cu3Oy like structure by 17O NMR. Measurements were made on underdoped and optimally doped powder samples from two families (x = 0.1 and 0.4). Maximum Tc varies by 30% with minimal structural changes between families. The spectrum differentiates two distinctive oxygen sites - planar and apical. Spin-lattice relaxation times on these two sites differ by more than an order of magnitude as oxygen in conductive plane relaxes much faster. NMR lines shift with respect to temperature occurs only on planar site, while the apical site shift is temperature independent. The temperature dependence of the planar oxygen Knight shift of underdoped and doped samples, shows opening of gap at temperatures high above Tc, (as previously indicated by magnetization measurements). Unlike YBCO, where optimally doped samples show no evidence of pseudogap forming, we observe opening of the gap even in optimally doped samples.

High-Tc; NMR; CaLaBaLaCuO

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