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arXiv 0810.0001cond-mat.str-el
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三角格上的Mottness

Mottness on a triangular lattice

Dimitrios Galanakis, Tudor Stanescu, Philip Phillips

摘要:

我们研究了钴酸盐相图顺磁侧的物理性质,$Na_{x}CoO_{2}$,采用非交叉近似(NCA)的细胞动力学平均场论(CDMFT),在三角晶格上的单带哈伯德模型。在低掺杂时,我们发现低能物理主要是由准无色散带。在半填充时,我们发现在$U_{c}=5.6\pm0.15t$处的金属-绝缘体转变弱依赖于团簇的大小。金属态的开始是通过在化学势处的相干峰的增长而发生的。远离半填充,在电子掺杂的制度,该系统是金属与一个大的,连续的费米表面,如实验所见。在空穴掺杂时,准非色散带出现在较低的Hubbard带的顶部,并控制低能物理。该带是非费米液体行为的明显特征,并且不能被任何弱耦合方法捕获。这种准非色散带在一定的掺杂范围内持续存在,已经在实验中观察到。我们还研究了赝能隙现象的背景下,一个三角形晶格,我们提出了一个新的框架来讨论赝能隙现象一般。这个框架涉及的低能物理的动量依赖特性和链接的外观的赝能隙的费米表面的重建,而不调用任何长程序或对称性破缺。在这个框架内,我们预测的存在一个赝隙的二维哈伯德模型的三角形晶格中的弱空穴掺杂制度。

英文摘要:

We study the physics on the paramagnetic side of the phase diagram of the cobaltates, $Na_{x}CoO_{2}$, with an implementation of cellular dynamical mean field theory (CDMFT) with the non-crossing approximation (NCA) for the one-band Hubbard model on a triangular lattice. At low doping we find that the low energy physics is dominated by a quasi-dispersionless band. At half-filling, we find a metal-insulator transition at $U_{c}=5.6\pm0.15t$ which depends weakly on the cluster size. The onset of the metallic state occurs through the growth of a coherence peak at the chemical potential. Away from half filling, in the electron-doped regime, the system is metallic with a large, continuous Fermi surface as seen experimentally. Upon hole doping, a quasi non-dispersing band emerges at the top of the lower Hubbard band and controls the low-energy physics. This band is a clear signature of non-Fermi liquid behavior and cannot be captured by any weakly coupled approach. This quasi non-dispersive band, which persists in a certain range of dopings, has been observed experimentally. We also investigate the pseudogap phenomenon in the context of a triangular lattice and we propose a new framework for discussing the pseudogap phenomena in general. This framework involves a momentum-dependent characterization of the low-energy physics and links the appearance of the pseudogap to a reconstruction of the Fermi surface without invoking any long range order or symmetry breaking. Within this framework we predict the existence of a pseudogap for the two dimensional Hubbard model on a triangular lattice in the weakly hole-doped regime.

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