17O NMR study of local hole density and spin dynamics in YBa2Cu4O8

✍ Scribed by Guo-qing Zheng; Yoshio Kitaoka; Kunisuke Asayama; Yasuharu Kodama; Yoshihiro Yamada

• Publisher: Elsevier Science
• Year: 1992
• Tongue: English
• Weight: 842 KB
• Volume: 193
• Category: Article
• ISSN: 0921-4534
• DOI: 10.1016/0921-4534(92)90882-d

✦ Synopsis

NMR has been carded out in YBa2Cu4Oa with T~= 74 K. The nuclear quadrupole tensors in the oxygen sites were determined and compared with those in other h, igh-T~ cuprates. The hole densities in the oxygen and copper sites have been extracted from v~(O) and vQ(Cu) by assuming that the electric field gradient is dominated by the on-site holes. We propose that the hole distribution (the extent of covalency) between the planar oxygens and copper, which is changed by doping and pressure, is a hidden parameter determining the spin dynamics and the superconducting transition temperature T¢ in high-]~ cuprates. It was found that 1 /Tt Tand the Knight shift of the planar oxygens decrease with lowering temperature in the norma! state. The nuclear relaxation rates of t70 and 63Cu in the CuO2 plane exhibit different behaviors at temperatures higher thau ~ 120 K, reflecting the different q-window of spin fluctuations, while both of them share the same T-dependence below ~ 120 K down to 55 K. This scaling of !/T~ between ~70 and 63Cu, which is also sccn in YBa2Cu307 ( Tc=92 K) and YBa2Cu306.63 ( To=60 K), seems to be essential for high-T¢ superconductivity.