Cu hyperfine coupling constants of HgBa2CaCu2O6+δ

We estimated the ratios of 63Cu hyperfine coupling constants in the double-layer high-T c superconductor HgBa2CaCu2O6+δ from the anisotropies in Cu nuclear spin-lattice relaxation rates and spin Knight shifts to study the nature of the ultraslow fluctuations causing the T 2 anomaly in the Cu nuclear spin-echo decay. The ultraslow fluctuations may come from uniform magnetic fluctuations spread around the wave vector q = 0, otherwise the electric origins.