Ferromagnetism and spin excitations in topological Hubbard models with a flat band
Ferromagnetism and spin excitations in topological Hubbard models with a flat band
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平带拓扑哈伯德模型中的铁磁性和自旋激发
DOI：
10.1103/physrevb.99.014407
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发表时间：
2018-10
影响因子：
3.7
通讯作者：
Li Jian-Xin
中科院分区：
文献类型：
--
作者：
Su Xiao-Fei;Gu Zhao-Long;Dong Zhao-Yang;Yu Shun-Li;Li Jian-Xin
研究了相互作用拓扑绝缘体中平带铁磁相的自旋1激发谱。作为范例，我们考虑四分之一填充正方形晶格哈伯德模型，其自由部分是具有拓扑非平凡且近乎平坦的电子带的$\pi$通量态，它可以实现Chern模型或$Z_2$ Hubbard模型。利用数值精确对角化方法，在近平带上进行投影，得到了Chern和Z2 Hubbard模型的铁磁自旋1激发谱，包括自旋波和Stoner连续谱。两种情况下的谱都表现出明显的色散，特别是对于Chern Hubbard模型，自旋波是无隙的，而对于$Z_2$ Hubbard模型，自旋波是有隙的。值得注意的是，在这两种情况下，自由电子带的非平坦性在斯通纳连续谱的下边界引入了凹陷。它显著地重整了这些向下倾斜的自旋波的能量，并导致了类似于旋子的自旋激发。我们阐述了这是软化的旋转式模式的铁磁相不稳定，并确定了铁磁相是稳定的参数区域。
We study the spin-1 excitation spectra of the flatband ferromagnetic phases in interacting topological insulators. As a paradigm, we consider a quarter filled square lattice Hubbard model whose free part is the $\pi$ flux state with topologically nontrivial and nearly-flat electron bands, which can realize either the Chern or $Z_2$ Hubbard model. By using the numerical exact diagonalization method with a projection onto the nearly-flat band, we obtain the ferromagnetic spin-1 excitation spectra for both the Chern and $Z_2$ Hubbard models, consisting of spin waves and Stoner continuum. The spectra exhibit quite distinct dispersions for both cases, in particular the spin wave is gapless for the Chern Hubbard model, while gapped for the $Z_2$ Hubbard model. Remarkably, in both cases, the nonflatness of the free electron bands introduces dips in the lower boundary of the Stoner continuum. It significantly renormalizes the energies of the spin waves around these dips downward and leads to roton-like spin excitations. We elaborate that it is the softening of the roton-like modes that destabilizes the ferromagnetic phase, and determine the parameter region where the ferromagnetic phase is stable.
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影响因子：
8.6
作者：
H. Tasaki
通讯作者：
H. Tasaki
影响因子：
56.9
作者：
Bernevig, B. Andrei;Hughes, Taylor L.;Zhang, Shou-Cheng
通讯作者：
Zhang, Shou-Cheng
影响因子：
56.9
作者：
Koenig, Markus;Wiedmann, Steffen;Zhang, Shou-Cheng
通讯作者：
Zhang, Shou-Cheng
影响因子：
8.6
作者：
Yi-Fei Wang;Z. Gu;C. Gong;D. Sheng
通讯作者：
Yi-Fei Wang;Z. Gu;C. Gong;D. Sheng
DOI：
10.1088/0953-8984/3/26/014
发表时间：
1991-07
期刊：
Journal of Physics: Condensed Matter
影响因子：
--
作者：
W von der Linden;D M Edwards
通讯作者：
W von der Linden;D M Edwards