Zhang Qiu, Li Tao
Department of Physics, Renmin University of China, Beijing 100872, People's Republic of China.
J Phys Condens Matter. 2021 Jul 14;33(37). doi: 10.1088/1361-648X/ac0f2d.
We find that the Schwinger boson mean field theory (SBMFT) supplemented with Gutzwiller projection provides an exceedingly accurate description for the ground state of the spin-12triangular lattice antiferromagnetic Heisenberg model (spin-12TLHAF). However, we find the SBMFT fails even qualitatively in the description of the dynamical behavior of the system. In particular, the SBMFT fails to predict the Goldstone mode in the magnetic ordered phase. We show that the coherent peak in the two-spinon continuum in the presence of spinon condensate should not be interpreted as a magnon mode. The SBMFT also predicts incorrectly a gapless longitudinal spin fluctuation mode in the magnetic ordered phase. We show that these failures are related to the following facts: (1) spinon condensation fails to provide a consistent description of the order parameter manifold of the 120 degree ordered phase. (2) There lacks in the SBMFT the coupling between the uncondensed spinon and the spinon condensate, which breaks both the spin rotational and the translational symmetry. (3) There lacks in the SBMFT the rigidity that is related to the no double occupancy constraint on the spinon system. We show that such failures of the SBMFT is neither restricted to the spin-12TLHAF nor to the magnetic ordered phase. We proposed a generalized SBMFT to resolve the first two issues and a new formalism to address the third issue.
我们发现，补充了古兹维勒投影的施温格玻色子平均场理论（SBMFT）为自旋 - 1/2三角晶格反铁磁海森堡模型（自旋 - 1/2 TLHAF）的基态提供了极其精确的描述。然而，我们发现SBMFT在描述该系统的动力学行为时甚至在定性方面都失败了。特别是，SBMFT未能预测磁有序相中的戈德斯通模式。我们表明，在存在自旋子凝聚的情况下，双自旋子连续体中的相干峰不应被解释为磁振子模式。SBMFT还错误地预测了磁有序相中的无隙纵向自旋涨落模式。我们表明这些失败与以下事实有关：（1）自旋子凝聚未能对120度有序相的序参量流形提供一致的描述。（2）SBMFT中缺乏未凝聚自旋子与自旋子凝聚之间的耦合，这破坏了自旋旋转和平移对称性。（3）SBMFT中缺乏与自旋子系统上的无双重占据约束相关的刚性。我们表明SBMFT的这种失败既不限于自旋 - 1/2 TLHAF，也不限于磁有序相。我们提出了一种广义的SBMFT来解决前两个问题，并提出了一种新的形式主义来解决第三个问题。
