Energy dependence of commensurate neutron scattering peak in the doped two-leg ladder antiferromagnetSr14−xCaxCu24O41

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 Sr 1 4 - x Ca x Cu 2 4 O 4 1 .