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Spin Casimir effect in noncollinear quantum antiferromagnets: Torque equilibrium spin wave approach

机译：非共线量子反铁磁体中的自旋卡西米尔效应：转矩平衡自旋波方法

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摘要

The Casimir effect is a general phenomenon in physics, which arises when the vacuum fluctuation of an arbitrary field is modified by static or a slowly varying boundary. However, its spin version is rarely addressed, mainly due to the fact that a macroscopic boundary in quantum spin systems is hard to define. In this paper, we explore the spin Casimir effect induced by the zero-point fluctuation of spin waves in a general noncollinear ordered quantum antiferromagnet. This spin Casimir effect results in a spin torque between local spins and further causes various singular and divergent results in the framework of spin-wave theory, which invalidate the standard 1/S expansion procedure. Based on the spin Casimir torque interpretation, we develop a spin-wave expansion approach named as torque equilibrium spin wave theory. In this approach, the spin Casimir effect is treated in a self-consistent way, and the spin-wave expansion results are free from singularities and divergences. A detailed spin-wave analysis of the antiferromagnetic spin-1/2 Heisenberg model on a spatially anisotropic triangular lattice is undertaken within our approach. Our results indicate that the spiral order is only stable in the region 0.5 ＜ α ＜ 1.2, where α is the ratio of the coupling constants. In addition, the instability in the region 1.2 ＜ α ＜ 2 is owing to the spin Casimir effect instead of the vanishing sublattice magnetization. Furthermore, our method provides an efficient and convenient tool that can estimate the correct exchange parameters and outline the quantum phase diagrams, which can be useful for experimental fitting processes in frustrated quantum magnets.
机译：卡西米尔效应是物理学中的一种普遍现象，当任意场的真空波动被静态或缓慢变化的边界所修正时，就会出现这种现象。但是，其自旋形式很少得到解决，这主要是由于难以定义量子自旋系统中的宏观边界这一事实。在本文中，我们探讨了在一般的非共线有序量子反铁磁体中，自旋波的零点波动引起的自旋卡西米尔效应。这种自旋Casimir效应会导致局部自旋之间的自旋转矩，并在自旋波理论的框架内进一步导致各种奇异和发散的结果，从而使标准的1 / S扩展程序无效。基于自旋Casimir转矩解释，我们开发了一种称为转矩平衡自旋波理论的自旋波扩展方法。在这种方法中，以自洽的方式处理自旋卡西米尔效应，自旋波扩展结果没有奇异和发散。在我们的方法中，对空间各向异性三角晶格上的反铁磁自旋1/2 Heisenberg模型进行了详细的自旋波分析。我们的结果表明，螺旋阶仅在0.5 ＜α＜1.2范围内稳定，其中α是耦合常数之比。另外，1.2 ＜α＜2区域的不稳定性是由于自旋卡西米尔效应而不是亚晶格磁化强度的消失。此外，我们的方法提供了一种有效且方便的工具，可以估算正确的交换参数并勾勒出量子相图，这对于在受挫的量子磁体中进行实验拟合过程很有用。

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  • 来源
    《Physical review》 |2015年第21期|214409.1-214409.12|共12页
  • 作者

    Z. Z. Du; H. M. Liu; Y. L. Xie; Q. H. Wang; J.-M. Liu;

  • 作者单位

    Laboratory of Solid State Microstructures and Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China;

    Laboratory of Solid State Microstructures and Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China;

    Laboratory of Solid State Microstructures and Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China;

    Laboratory of Solid State Microstructures and Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China;

    Laboratory of Solid State Microstructures and Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China;

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  • 正文语种 eng
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  • 关键词

    spin waves; quantized spin models; antiferromagnetics; quantum fluctuations, quantum noise, and quantum jumps;

    机译：自旋波量化自旋模型反铁磁量子涨落;量子噪声和量子跃迁;

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