Pseudo spin gap in high-T-c's manifested by the NMR experiments

From the temperature dependence of the Cu-63 nuclear spin-lattice relaxation rate, 1/T1T, in the planar Cu(2) sites, it is well established by now that highly enhanced and strongly temperature dependent relaxation process due to antiferromagnetic Cu spin fluctuations exhibits the opening of a pseudo gap in the low-lying magnetic excitations with an energy comparable to the superconducting gap, particularly for the so-called low doping region. It is also found that, irrespective of the single-layer or the bi-layrer system, the temperature at which the spin-gap opens, T-sg, determined as the peak of 1/T1T vs. T, has a linear decrease with increasing of the doping concentration. A general spin-gap phase diagram is proposed.