Spin and Hole Dynamics in Carrier-Doped Quantum Haldane Chain

Quantum spins in one-dimensional (1D) chains exhibit characteristic features such as the Haldane gap (S 1) and the spin-Peierls state (S 1/2). Multiple degrees of freedom associated with quantum spins have recently become a focus of attention. We present here the spin dynamics in lightly hole-doped Nd2-xCaxBaNiO5 (x 0.1), a 1D Haldane system, using pulsed neutron inelastic scattering. The entire dispersion of the 1D Haldane chain was clearly observed with a ~14 meV spin gap (Haldane gap) at the magnetic zone center. Below the gap, much spectral weight was observed, indicating an in-gap state possibly originating from the doped holes in Haldane chains.