Bi₂CuO₄中磁性的格林函数理论：各向异性海森堡XYZ模型
Green's function theory of magnetism in Bi$_2$CuO$_4$: anisotropic Heisenberg XYZ model
AI总结：
本文将Lymar和Rudoi的格林函数理论推广到共线自旋1/2反铁磁体多亚晶格磁相互作用场景，应用于Bi₂CuO₄，计算其磁激发相关参数，推导奈尔温度并结合实验参数得到T_N≈52 K。
AI中文摘要：
将Lymar和Rudoi的格林函数理论[《理论与数学物理》第21卷，990页（1974年）]推广到共线自旋1/2反铁磁体中多个亚晶格内和亚晶格间磁相互作用的场景，并应用于Bi₂CuO₄的磁激发研究。自旋哈密顿量包含面外和面内对称各向异性项，以及描述与沿奈尔矢量方向施加的外磁场B相互作用的塞曼项。在自旋波近似下，我们计算了自旋激发色散、反铁磁共振频率以及自旋翻转变磁跃迁的临界场B_c。研究表明，弱的面内各向异性会在类声学激发分支中产生能隙，该能隙非线性依赖于外磁场，并在B=B_c时闭合。推导了零场下Tyablikov随机相位近似中的奈尔温度表达式，结合Yuan等人[《物理评论B》第103卷，134436页（2021年）]近期非弹性中子散射研究得到的参数，该表达式给出T_N≈52 K。
英文摘要：
The Green's function theory of Lymar' and Rudoi [Theor. Math. Phys. vol. 21, 990 (1974)] is generalized to the case of multiple intra- and inter-sublattice magnetic interactions in a collinear spin-half antiferromagnet and applied to magnetic excitations in Bi$_2$CuO$_4$. The spin Hamiltonian includes both the out-of-plane and in-plane symmetric anisotropy terms and the Zeeman term, which describes the interaction with an external magnetic field $B$ applied along the Néel vector. Within the spin-wave approximation we calculate spin excitation dispersion, antiferromagnetic resonance frequencies and the critical field $B_c$ of the spin-flop metamagnetic transition. A weak in-plane anisotropy is shown to result in a gap in the acoustic-like branch of the excitations. The gap nonlinearly depends on the external field and closes at $B=B_c$. An expression for the Neel temperature in the Tyablikov random phase approximation at zero field is derived. For the parameters derived from the recent inelastic neutron scattering study by Yuan et al. [Phys. Rev. B vol. 103, 134436 (2021)] it gives $T_{\rm N}\approx 52$~K.
