Non-linear bond-operator theory and 1/d expansion for coupled-dimer magnets I: Paramagnetic phase
Non-linear bond-operator theory and 1/d expansion for coupled-dimer magnets I: Paramagnetic phase
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DOI：
10.1103/physrevb.91.094404
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发表时间：
2014-07
影响因子：
3.7
通讯作者：
D. G. Joshi;K. Coester;K. Schmidt;M. Vojta
中科院分区：
文献类型：
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作者：
D. G. Joshi;K. Coester;K. Schmidt;M. Vojta
对于耦合二聚体海森堡磁体，磁量子相变的一个范例，我们开发了一个系统的扩展在1/d，空间维度的倒数。展开采用了键算符技术的公式，并基于这样的观察：适当选择的乘积态波函数在d->infty极限下产生局部观测值的精确零温度期望值，校正值为1/d。我们展示了一个超立方晶格上的二聚体模型的方法，它将正方晶格双层海森堡模型推广到任意d。在本文中，我们使用1/d展开计算静态和动态观测值在零温度下的顺磁单态相，量子相变，并比较结果与数值数据为d=2。联系也与以前提出的改进键运营商的理论，以及与微扰膨胀的二聚体间的耦合。在一个配套文件中，目前的1/d扩展将被扩展到有序相，在那里它是一致的描述整个相图，包括量子临界点。
For coupled-dimer Heisenberg magnets, a paradigm of magnetic quantum phase transitions, we develop a systematic expansion in 1/d, the inverse number of space dimensions. The expansion employs a formulation of the bond-operator technique and is based on the observation that a suitably chosen product-state wavefunction yields exact zero-temperature expectation values of local observables in the d->infty limit, with corrections vanishing as 1/d. We demonstrate the approach for a model of dimers on a hypercubic lattice, which generalizes the square-lattice bilayer Heisenberg model to arbitrary d. In this paper, we use the 1/d expansion to calculate static and dynamic observables at zero temperature in the paramagnetic singlet phase, up to the quantum phase transition, and compare the results with numerical data available for d=2. Contact is also made with previously proposed refinements of bond-operator theory as well as with a perturbative expansion in the inter-dimer coupling. In a companion paper, the present 1/d expansion will be extended to the ordered phase, where it is shown to consistently describe the entire phase diagram including the quantum critical point.