Study of Haldane Gap Problem Use of Magnetic and Magneto-Optical Measurements in High Magnetic Fields.

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We have studied the Haldane gap problems by use of magnetic and spectral measuements. Our proposed model explains that the origin of the gap arises from the excitation of spin pair in the linear S=1 spin chain with the gap of exchange parameter J. Moreover, the gap is decreased by the dispersion effect, because of the RVB-Like motion of the spin pair. We have made following various experimental study to confirm our model: 1) we, at first, developed the determination method of the gap by use of the onset field H_c of the magnetization. By comparing with ESR experiment, we could find the best position as H_c around the rounding onset of the magnetization. The onset of the magnetization is observed along all crystal axes. The fact is characterized the Haldane effect and is completely different from the magnetization onset arising from the anisotropy. 2) we could experimentally determine the relation E_g=0.41J between the gap energy E_g and J by use of the method in 1) for various crystals. 3)we could confirm no Halden-like gap for the one dimensional S=1/2 spin system in CsCoCl_3. We could fined other various magnetic excitations in the spectroscopy experiment. 4)we could determine the excited energy level structure at zero momentum k=0 by use of the spectroscopic method of ESR experiment. 5)some excess moment around unpaired spins in the S=1 spin chain made by impurity ions were observed, which has been predicted by our model. 6)the effect of 5) could not found in S=1/2 spin system in CsCo_<1-x>Mg_xCl_3 and we could observed other small step-magnetizations in the spin system. Our these experimantal results are now introducting new important and basic problems in the quantum statuistical problems such as an effect on the spin correlation by the dif-ference in the boundary condition at the impurity. We hope that our results can contribute the development of these new basic problems.