The dynamical spin response of doped two-leg ladder antiferromagnets is investigated based on the fermion-spin approach. Our calculations clearly demonstrate a crossover from incommensurate antiferromagnetism in the weak-interchain-coupling regime to commensurate spin fluctuation in the strong-interchain-coupling regime. In particular, the nuclear spin-lattice relaxation rate extracted from the commensurate spin fluctuation decreases exponentially with decreasing temperatures. The behaviors of the spin dynamics in the strong-coupling regime are quantitatively close to the experimental results of Sr14-xCaxCu24O41.
Physical Review B (Condensed Matter and Materials Physics) 67(9), 094402(6 pages)