Spinon confinement in a quasi-one-dimensional anisotropic Heisenberg magnet
Spinon confinement in a quasi-one-dimensional anisotropic Heisenberg magnet
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DOI：
10.1103/physrevb.96.054423
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发表时间：
2017-08-17
影响因子：
3.7
通讯作者：
Quintero-Castro, D. L.
中科院分区：
文献类型：
--
作者：
Bera, A. K.;Lake, B.;Quintero-Castro, D. L.
限制是具有分数量子数的粒子结合在一起形成具有整数量子数的准粒子的过程。组成颗粒受到吸引力相互作用的限制，吸引力相互作用的强度随着颗粒分离的增加而增加，因此，单个颗粒并不是孤立存在的。这种现象在粒子物理学中众所周知，夸克被限制在重子和介子中。类似的现象发生在某些空间各向异性磁绝缘体中。这些可以被认为是自旋弱耦合链 S = 1/2，因此自旋翻转携带整数自旋 S = 1。这些系统中的集体激发（称为自旋子）结果携带分数自旋量子数 S = 1/2。有趣的是，在足够低的温度下，链之间的弱耦合可以引起自旋子对之间的吸引力相互作用，这种相互作用随着它们的分离而增加，从而导致限制。在本文中，我们采用非弹性中子散射来研究具有海森堡伊辛（XXZ）各向异性 SrCo2V2O8 的准一维自旋 1/2 反铁磁体中的自旋约束过程。探索了高于和低于长程有序温度 T-N = 5.2 K 的宽温度范围。在 TN 上方观察到自旋激发，与既定理论定量一致。下面的 T-N 对自旋子被限制，并且观察到具有纵向和横向极化的两个类介子束缚态序列。使用多种理论方法来解释数据。这些基于一维 S = 1/2 XXZ 反铁磁自旋链的描述，其中链间耦合通过有效的交错平均磁场进行建模。研究了广泛的交换各向异性，并确定了 SrCo2V2O8 特有的参数。最近开发的基于切空间矩阵乘积态的理论技术给出了数据的非常完整的描述，并且不仅与束缚模式的能量而且与它们的强度也提供了良好的一致性。我们还成功地解释了温度对激发的影响，包括实验观察到的 T-N 以下纵向模式之间的热致共振以及 T-N 以上热激发自旋子态之间的跃迁。总之，我们的工作将 SrCo2V2O8 确立为准一维量子磁体中自旋限制的美丽范例，并提供了该过程的全面图片。
Confinement is a process by which particles with fractional quantum numbers bind together to form quasiparticles with integer quantum numbers. The constituent particles are confined by an attractive interaction whose strength increases with increasing particle separation and, as a consequence, individual particles are not found in isolation. This phenomenon is well known in particle physics where quarks are confined in baryons and mesons. An analogous phenomenon occurs in certain spatially anisotropic magnetic insulators. These can be thought of in terms of weakly coupled chains of spins S = 1/2, and a spin flip thus carries integer spin S = 1. The collective excitations in these systems, called spinons, turn out to carry fractional spin quantum number S = 1/2. Interestingly, at sufficiently low temperatures the weak coupling between chains can induce an attractive interaction between pairs of spinons that increases with their separation and thus leads to confinement. In this paper, we employ inelastic neutron scattering to investigate the spinon-confinement process in the quasi-one-dimensional, spin-1/2 antiferromagnet with Heisenberg-Ising (XXZ) anisotropy SrCo2V2O8. A wide temperature range both above and below the long-range ordering temperature T-N = 5.2 K is explored. Spinon excitations are observed above TN in quantitative agreement with established theory. Below T-N pairs of spinons are confined and two sequences of meson-like bound states with longitudinal and transverse polarizations are observed. Several theoretical approaches are used to explain the data. These are based on a description in terms of a one-dimensional, S = 1/2 XXZ antiferromagnetic spin chain, where the interchain couplings are modeled by an effective staggered magnetic mean field. A wide range of exchange anisotropies are investigated and the parameters specific to SrCo2V2O8 are identified. Recently developed theoretical technique based on tangent-space matrix product states gives a very complete description of the data and provides good agreement not only with the energies of the bound modes but also with their intensities. We also successfully explain the effect of temperature on the excitations including the experimentally observed thermally induced resonance between longitudinal modes below T-N and the transitions between thermally excited spinon states above T-N. In summary, our work establishes SrCo2V2O8 as a beautiful paradigm for spinon confinement in a quasi-one-dimensional quantum magnet and provides a comprehensive picture of this process.