Exact one- and two-particle excitation spectra of acute-angle helimagnets above their saturation magnetic field
Exact one- and two-particle excitation spectra of acute-angle helimagnets above their saturation magnetic field
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DOI：
10.1103/physrevb.75.024401
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发表时间：
2007-01-01
影响因子：
3.7
通讯作者：
Drechsler, S. -L.
中科院分区：
文献类型：
--
作者：
Kuzian, R. O.;Drechsler, S. -L.
考虑受抑 XXZ 自旋 1/2 海森堡哈密顿量和超过饱和场 B(s) 的外部磁场的双磁振子问题。我们证明该问题可以准确地映射到有效的紧束缚杂质问题。它允许获得任意维度和相互作用数量的二磁振子格林函数的显式精确表达式。我们将该理论应用于具有铁磁最近邻 J(1) < 0 和反铁磁次近邻 J(2) > 0 相互作用的准一维螺旋磁体。激发光谱的一个突出特征是存在双磁振子束缚态。这导致饱和场 B(s) 偏离其经典值 Bs cl ，这与单磁振子不稳定性一致。对于精化挫败比垂直条 J(2)/J(1)垂直条 > 0.374 661，二磁振子谱的最小值出现在布里渊区的边界处。基于双磁振子方法，我们提出了饱和场 B(s) 的一般解析表达式，证实了先前已知的一维各向同性系统的结果，但也探索了链间和长程链内相互作用以及交换各向异性的作用。
The two-magnon problem for the frustrated XXZ spin-1/2 Heisenberg Hamiltonian and external magnetic fields exceeding the saturation field B(s) is considered. We show that the problem can be exactly mapped onto an effective tight-binding impurity problem. It allows to obtain explicit exact expressions for the two-magnon Green's functions for arbitrary dimension and number of interactions. We apply this theory to a quasi-one-dimensional helimagnet with ferromagnetic nearest-neighbor J(1) < 0 and antiferromagnetic next-nearest neighbor J(2) > 0 interactions. An outstanding feature of the excitation spectrum is the existence of two-magnon bound states. This leads to deviations of the saturation field B(s) from its classical value Bs cl which coincides with the one-magnon instability. For the refined frustration ratio vertical bar J(2)/J(1)vertical bar > 0.374 661 the minimum of the two-magnon spectrum occurs at the boundary of the Brillouin zone. Based on the two-magnon approach, we propose general analytic expressions for the saturation field B(s), confirming known previous results for one-dimensional isotropic systems, but explore also the role of interchain and long-ranged intrachain interactions as well as of the exchange anisotropy.