阻挫对准一维非对称子格反铁磁链自旋波激发的影响

子格对称性破缺使得s=1/2准一维海森伯自旋链具有三支自旋波激发谱(其中一支属于声学模，两支属于光学模). 计算表明：阻挫导致两支光学模能隙简并解除；阻挫引起声学模自旋波激发谱软化，但并不导致光学模激发谱软化；阻挫导致两支光学模激发谱中的一支明显下移，这意味着阻挫使光学模激发变得重要且容易实现；阻挫引起的自旋偏离对于属于不同子格的自旋是不同的；阻挫对于系统基态磁性长程序的削弱随着阻挫增强变得越来越明显. 通过与严格对角化方法和DMRG方法的数值结果比较，还分析了自旋波近似的合理性和不足之处. 关键词： 准一维反铁磁自旋系统 自旋波激发 光学模 能隙简并

Effect of frustration on spin-wave excitation of the quasi-one-dimensional antiferromagnetic chain with asymmetrical sublattices

The s=1/2 quasi-one-dimensional Heisenberg antiferromagnetic chain with asymmetrical sublattices possesses three branches of spin-wave spectra (one in acoustic mode and the other two in optical mode). The frustration relieves the gap-degeneracy of two optical branches and softens the spectrum in acoustic mode, but doesn't soften the spectra in optical mode. Also, the frustration moves down obviously one of the two spectra in optical mode. It means that the frustration makes the spin-wave excitation described by spectrum in optical mode easier and more important. The status of spin on the chain changes more easily than that of side spin under the effect of frustration. The weakening of magnetic order in ground state becomes strong with the strengthening of frustration. By comparison with numerical results of exact diagonalization and DMRG methods, we discuss the merit and drawbacks of the spin-wave approximation.