SYSTEMATIC NMR-STUDIES OF HIGH-T-C AND 2-LEG SPIN-LADDER SYSTEMS

We review systematic NMR studies on underdoped high-T-c cuprates and t wo-leg spin-ladder systems, focusing on their spin gap and dynamics. T he pressure-induced superconductivity was discovered in Sr14-xCaxCu24O 41 comprising the quasi-one-dimensional S = 1/2 two-leg spin-ladder Cu 2O3 planes. Remarkably, the new parent cuprate is the Mott insulator w ith the spin gap in contrast to the antiferromagnetic (AF) insulator f or the high-T-c cuprates. From the Cu-NMR results in the ladder Cu2O3 plane on single crystals Sr14-xCaxCu24O41 with x = 9 (hereafter denote d as Ca9) and x = 11.5 (Ca11.5), it is shown that the spin gap, Delta = 510 K in the Sr14 is significantly reduced upon isovalent Ca substit ution, but its magnitude remains nearly constant with Delta = 270 and 280 K for the Ca9 and Ca11.5, respectively. In T range of T greater th an or equal to d, the spin dynamics in carrier-doped two-leg spin-ladd er systems are characterized by the behaviour similar to the S = 1/2 1 D Heisenberg system. By contrast, the transport property shares a comm on feature, i.e, due to the spin-gap opening the charge transport is c onfined in the 2D CuO2 plane for underdoped high-T-c cuprates and in t he quasi-1D ladder for spin-ladder compounds. (C) 1998 Elsevier Scienc e B.V. All rights reserved.