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arXiv 1506.06145cond-mat.str-el
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单交叉近似描述Mott跃迁的可靠性

Reliability of the one-crossing approximation in describing the Mott transition

V. Vildosola, L. V. Pourovskii, L. O. Manuel, P. Roura-Bas

摘要:

我们评估的可靠性的一个交叉近似(OCA)的方法在定量描述的莫特过渡的框架内的动力学平均场论(DMFT)。OCA方法已被应用于与DMFT结合的一些重费米子,锕系元素,过渡金属化合物,和纳米级系统。然而,最近在杂质模型框架内的一些研究指出了OCA的严重缺陷,并对其可靠性提出了质疑。在这里,我们考虑一个单带哈伯德模型的Bethe晶格在有限的温度和比较OCA的结果的数值精确的量子蒙特卡罗(QMC)方法。在粒子-空穴对称情况下,OCA得到的温度-局域排斥U相图与QMC的结果吻合得很好,并且很好地捕捉到了金属-绝缘体相变。然而,我们发现,绝缘体到金属的过渡被转移到更高的值的U,同时,在金属相的相关性显着高估。这种违反直觉的行为是由于同时低估了金属相的近藤尺度和绝缘间隙的大小。我们跟踪低估的绝缘间隙的杂质谱密度的高频扩展的二阶矩。计算系统远离粒子-空穴对称的情况下,也提出和讨论。

英文摘要:

We assess the reliability of the one-crossing approximation (OCA) approach in quantitative description of the Mott transition in the framework of the dynamical mean field theory (DMFT). The OCA approach has been applied in the conjunction with DMFT to a number of heavy-fermion, actinide, transition metal compounds, and nanoscale systems. However, several recent studies in the framework of impurity models pointed out to serious deficiencies of OCA and raised questions regarding its reliability. Here we consider a single band Hubbard model on the Bethe lattice at finite temperatures and compare the results of OCA to those of a numerically exact quantum Monte Carlo (QMC) method. The temperature-local repulsion U phase diagram for the particle-hole symmetric case obtained by OCA is in good agreement with that of QMC, with the metal-insulator transition captured very well. We find, however, that the insulator to metal transition is shifted to higher values of U and, simultaneously, correlations in the metallic phase are significantly overestimated. This counter-intuitive behavior is due to simultaneous underestimations of the Kondo scale in the metallic phase and the size of the insulating gap. We trace the underestimation of the insulating gap to that of the second moment of the high-frequency expansion of the impurity spectral density. Calculations for the system away from the particle-hole symmetric case are also presented and discussed.

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