Spin dynamics in S=1/2 chains and ladders from NMR and susceptibility measurements in Sr14-xNaxCu24O41

The authors report on NMR and susceptibility measurements in Sr14-xNaxCu24O 41 for 0 less than or equal to x less than or equal to 2 The analysis of th e susceptibility evidences that only a small fraction of Cu2+ spins are inv olved in the dimerization of Cu(1)O-2 chains. The introduction of extra hol es by Na+ doping is found to decrease the Cu(1)(2+) uniform static suscepti bility without affecting the amplitude of the dimerization gap. On the othe r hand, the amplitude of the spin gap in the Cu(2)(2)O-3 two-leg-ladders an d the resistivity are reduced by doping. The origin of the discrepancy in t he amplitude of the gap estimated by means of nuclear spin-lattice relaxati on and susceptibility measurements is briefly discussed. (C) 1998 American Institute of Physics.