Weak pseudogap in crystals of Pb2Sr2(Y,Ca)Cu3O8+δ

We report on NMR measurements in underdoped Pb2Sr2(Y,Ca)Cu3O8+δ crystals. A pseudogap is observed in the Knight shift and spin-lattice relaxation rate. In contrast to other underdoped compounds, the pseudogap observed in the Knight shift is weak and occurs at a significantly lower temperature. On the other hand, the effect the pseudogap has on spin-lattice relaxation is quite similar to that in other compounds. The contrast between weak and strong pseudogaps is discussed.