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arXiv 1809.01929cond-mat.str-el
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窄禁带半导体FeSi中的关联激发态和局域自旋矩的反铁磁屏蔽

Correlated excited states in the narrow gap band semiconductor FeSi and antiferromagnetic screening of local spin moments

Sergii Khmelevskyi, Georg Kresse, Peter Mohn

摘要:

半导体FeSi具有非常窄的带隙、磁化率的反常行为和高温下的金属-绝缘体转变的物理性质引起了人们的极大兴趣,这是由于对它们起源的理论理解仍然存在争议。一方面,在低温下在FeSi中形成带隙的纯带状机制已经很好地建立,另一方面,大量的实验和它们的理论解释表明在有限温度下具有强相关性的丰富物理。在这项工作中,我们使用一个从头算方案的基础上的随机相位近似和局域自旋密度近似(RPA@LSDA),以揭示电子相关效应在FeSi中的作用,通过施加一个固定的自旋矩约束。在无参数框架下,我们发现关联效应从根本上改变了单电子LSDA结果,导致在Fe上形成一个具有有限磁矩的附加态,其能量几乎与非磁性基态简并.这解释了高场实验的结果,该实验发现了一阶亚磁性相变到金属铁磁状态。我们的研究结果表明,在FeSi的低能量激发强相关的性质。从我们的超细胞计算,我们发现,这些激发是本地的,并表现出近藤样的行为,因为一个强大的反铁磁屏蔽。

英文摘要:

The physical properties of the semiconductor FeSi with very narrow band gap, anomalous behavior of the magnetic susceptibility and metal-insulator transition at elevated temperatures attract gross interest due to the still controversial theoretical understanding of their origin. On one side the purely band like mechanism of the gap formation in FeSi at low temperature is well established, on other side a number of experiments and their theoretical interpretation suggest a rich physics of strong correlations at finite temperature. In this work we use an ab-initio scheme based on the Random Phase Approximation and Local Spin Density Approximation (RPA@LSDA) to reveal the role of the electron correlation effects in FeSi extending it by applying a fixed spin moment constraint. In the parameter free framework we show that correlation effects essentially alter the one-electron LSDA results leading to the formation of an additional state with finite magnetic moment on Fe, whose energy is almost degenerate with the non-magnetic ground state. This explains the results of high field experiments, which found a first-order meta-magnetic phase transition into a metallic ferromagnetic state. Our results suggest a strongly correlated nature of the low-energy excitations in FeSi. From our super-cells calculations we reveal that these excitations are local and exhibit a Kondo-like behavior since a strong antiferromagnetic screening is present.

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