含阻挫和各向异性的反铁磁自旋链的键算符理论

Bond operator theory of antiferromagnetic spin chain with bond alternation and anisotropy

基于键算符平均场近似,讨论了阻挫和单粒子各向异性对自旋为1的反铁磁自旋链的影响。通过求解自恰方程,得到了低能激发能谱、自由能、静态磁化率和比热容。系统激发态能谱的能隙分别在阻挫和单粒子各向异性的影响下转变为0,这意味着存在量子相变。阻挫诱导的临界点是在α为1.39和D为-0.35,α是相邻格点之间的阻挫比值,D是沿z轴方向的各向异性因子。计算的相变临界点与其他数值方法的结果是一致的。

Based on the bond operation mean-field approximation, the effects of bond alternation and single-ion anisotropy on an S=1 antiferromagnetic spin chain were discussed. The energy spectrums,free energy, static susceptibility and specific heat capacity were obtained by solving the self-consistent equations. The system can be transited from gapful to gapless which means the existence of quantum phase transition. The phase transition can be induced by bond alternation at α=1.39 and anisotropy at D=-0.35 respectively. The critical points of these transitions are qualitatively consistent with the previous numerical results by other methods.