Transverse Antiferromagnetism of a Magnetized Haldane-Gap System

Abstract

A 1D S=1 Heisenberg antiferromagnet in a magnetic field H(⁄⁄z-axis) at T=0 is studied by numerical diagonalizations. It is found that a phase transition exists at H_c1(=Δ), where Δ is the Haldane gap, and the transverse staggered susceptibility χ_st^xx diverges and the spin correlation is asymptotically ⟨S₀^xS_r^x⟩∼(−1)^rr^−η between H_c1 and H_c2(=4). If the system is quasi-1D, even small interchain interactions can make canting Néel order within a mean field approximation for interchain interactions. This is consistent with a recent NMR measurement for NENP at low temperature.