Large magnetic heat transport in a Haldane chain material Ni(C$_3H_{10}N_2)_2NO_2ClO_4

Abstract: We report a study on the heat transport of an S = 1 Haldane chain compound Ni(C_3H_{10}N_2)_2NO_2ClO_4 at low temperatures and in magnetic fields. The zero-field thermal conductivities show a remarkable anisotropy for the heat current along the spin-chain direction (\kappa_b) and the vertical direction (\kappa_c), implying a magnetic contribution to the heat transport along the spin-chain direction. The magnetic-field-induced change of the spin spectrum has obviously opposite impacts on \kappa_b and \kappa_c. In particular, \kappa_b(H) and \kappa_c(H) curves show peak-like increases and dip-like decreases, respectively, at \sim 9 T, which is the critical field that minimizes the spin gap. These results indicate a large magnetic thermal transport in this material.