Frequency, linewidth and relaxation of Cu NQR signals in the superconductor Y Ba_1.9Ca_0.1Cu₄O_{8 ± y}

Abstract

The Cu NQR spectrum in Ca doped Y Ba2Cu4O8 (Tc = 90 K with 10 % Ca) has been measured between 18 and 40 MHz. The resonance signals for both Cu sites show no frequency shifts compared to the undoped material. By observing an additional peak at 20.600 MHz which is identified as a Cu1 signal, it is concluded that most if not all Ca ions substitute Ba rather than Y. The spin-lattice relaxation rate has, for both sites, a similar temperature dependence as in the pure material. It is only the spin-spin relaxation time that seems to be influenced by the Ca doping. © 1990.