The Haldane State in CsNiCl3Detected by Magnetization Measurements –Observation of Quantum-Classical Crossover and the Valence Bond Solid State–

Abstract

We have confirmed from susceptibility and magnetization measurements that the Haldane state really exists in 1D phase of CsNiCl 3 which undergoes 3D ordering at T N =4.8 K. The observed susceptibility at low fields follows the predicted curve for the S =1 quantum chain with energy gap (Δ/ k B ∼10 K) down to near T N . A more definite evidence for the Haldane state is given by studying the effect of the nonmagnetic impurities. We have revealed a real existence of S =1/2 edge states characteristic of the Haldane state and further revealed a crossover from the quantum to classical regimes as a function of both temperature and field. The result is consistent with the model that at low temperatures ( T | J |/ k B ) and high fields ( H > H G ) the system is not in the Haldane state any more.