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arXiv 1102.0592cond-mat.str-el
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冰规则局域约束下局域电荷阻挫系统耦合引起的金属-绝缘体相变

Metal-insulator transition caused by the coupling to localized charge-frustrated systems under ice-rule local constraint

Hiroaki Ishizuka, Masafumi Udagawa, Yukitoshi Motome

摘要:

本文报道了我们对费米子系统的电子和输运性质的理论和数值研究结果。我们考虑一个扩展的Falicov-Kimball模型,在该模型中,巡回的无自旋费米子相互排斥的U与本地化的粒子,其分布满足局部约束下的几何挫折,所谓的冰规则。我们数值计算了烧绿石,棋盘格和kagome晶格上的模型的态密度,光学电导率和逆参与比,并讨论了在相称填充的金属-绝缘体转变的性质。其结果是,我们表明,冰规则的本地约束导致在电子结构中的几个普遍的功能;一个电荷间隙打开在一个相当小的U相比的带宽,和能谱接近的特征形式在大U限制,即,在一维或$δ$功能峰的非相互作用的紧束缚形式。在大U区域中,流动费米子被限制在宏观简并的冰规则配置中,该配置由一堆一维环组成:我们称这种绝缘状态为电荷冰。另一方面,输运性质受晶格的几何形状和维数的影响很大;例如,烧绿石晶格模型通过增加U表现出从金属态到电荷-冰绝缘态的转变,而棋盘格晶格模型在打开间隙之前表现出安德森局域化。同时,在kagome格点情况下,我们没有得到明确的安德森局域化的证据。我们的结果阐明了在完全阻挫晶格中电荷-冰绝缘体相变的普遍性和多样性。

英文摘要:

We report the results of our theoretical and numerical study on electronic and transport properties of fermion systems with charge frustration. We consider an extended Falicov-Kimball model in which itinerant spinless fermions interact repulsively by U with localized particles whose distribution satisfies a local constraint under geometrical frustration, the so-called ice rule. We numerically calculate the density of states, optical conductivity, and inverse participation ratio for the models on the pyrochlore, checkerboard, and kagome lattices, and discuss the nature of metal-insulator transitions at commensurate fillings. As a result, we show that the ice-rule local constraint leads to several universal features in the electronic structure; a charge gap opens at a considerably small U compared to the bandwidth, and the energy spectrum approaches a characteristic form in the large U limit, that is, the noninteracting tight-binding form in one dimension or the $δ$-functional peak. In the large U region, the itinerant fermions are confined in the macroscopically-degenerate ice-rule configurations, which consist of a bunch of one-dimensional loops: We call this insulating state the charge ice. On the other hand, transport properties are much affected by the geometry and dimensionality of lattices; e.g., the pyrochlore lattice model exhibits a transition from a metallic to the charge-ice insulating state by increasing U, while the checkerboard lattice model appears to show Anderson localization before opening a gap. Meanwhile, in the kagome lattice case, we do not obtain clear evidence of Anderson localization. Our results elucidate the universality and diversity of phase transitions to the charge-ice insulator in fully frustrated lattices.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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