具有双二次相互作用的s=1反铁磁海森堡链的能谱

Excitation Spectra in the Spin-1 Antiferromagnetic Heisenberg Chain with Biquadratic Exchange Interaction

本文应用二阶格林函数方法，研究了双二次相互作用项（a）对反铁磁海森堡链激发谱的影响，目前用二阶格林函数方法研究此类问题尚未见报导．研究发现随着双二次相互作用的增强，反铁磁海森堡链的Haldane能隙将降低，并且存在一个双二次相互作用的临界值ac，当a＞ac时，将得不到体系的激发谱．我们的结果定性上与键算符方法研究具有双二次相互作用的反铁磁海森堡链能谱得到的结论一致．

The effect of the biquadratic exchange on the excitation spectra of the antiferrornagnetic Heisenberg chain (AFHC) is investigated by using second-order Green, s Function method. It is found that the Haldane gap will decrease with the increase of the biquadratic exchange interaction and it is interesting that there exists a critical value of the biquadratic exchange parameter ac= 0. 21 at T= 0K, when a＞ac, but not the excitation spectrum of the AFHC.