Electronic Origin of Tc in Bulk and Monolayer FeSe
Electronic Origin of Tc in Bulk and Monolayer FeSe
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DOI：
10.3390/sym13020169
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发表时间：
2019-08
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影响因子：
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通讯作者：
Swagata Acharya;D. Pashov;François Jamet;M. Schilfgaarde
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文献类型：
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作者：
Swagata Acharya;D. Pashov;François Jamet;M. Schilfgaarde
FeSe被归类为洪德金属，在费米能级附近具有多个d带。Hund金属中的相关性主要来源于交换参数J，它可以驱动相关性中的强轨道选择性。铁硫属元素是铁基超导体中关联最强的，其中dxy是关联最强的轨道。然而，很少有人知道这种关联是否以及如何直接影响洪德系统中的超导不稳定性。通过应用最近发展的从头算理论，我们明确地显示在dxy和超导临界温度Tc的相关性之间的连接。从从头算结果作为参考，我们考虑各种各样的参数空间中的参考周围的偏移，以确定是什么控制Tc。我们表明，J的小偏移可以引起Tc的巨大变化。此外，我们考虑通过改变Fe-Se键长在体中，在独立的单层M-FeSe，和M-FeSe上的SrTiO 3基板（M-FeSe/STO）跳跃的变化。接近的dxy状态的费米能量的孪生条件，和J的强度出现作为非相干光谱响应和增强的单粒子和双粒子散射，反过来控制Tc的主要标准。使用c-RPA，我们进一步表明，FeSe在单层形式（M-FeSe）提供了一个自然的机制，以提高J.我们解释了为什么M-FeSe/STO具有高Tc，而M-FeSe在隔离不应该。我们的研究打开了一个统一的理解是什么控制Tc的大块，层，和接口的Hund的金属空穴袋和电子屏蔽云工程的范例。
FeSe is classed as a Hund’s metal, with a multiplicity of d bands near the Fermi level. Correlations in Hund’s metals mostly originate from the exchange parameter J, which can drive a strong orbital selectivity in the correlations. The Fe-chalcogens are the most strongly correlated of the Fe-based superconductors, with dxy the most correlated orbital. Yet little is understood whether and how such correlations directly affect the superconducting instability in Hund’s systems. By applying a recently developed ab initio theory, we show explicitly the connections between correlations in dxy and the superconducting critical temperature Tc. Starting from the ab initio results as a reference, we consider various kinds of excursions in parameter space around the reference to determine what controls Tc. We show small excursions in J can cause colossal changes in Tc. Additionally we consider changes in hopping by varying the Fe-Se bond length in bulk, in the free standing monolayer M-FeSe, and M-FeSe on a SrTiO3 substrate (M-FeSe/STO). The twin conditions of proximity of the dxy state to the Fermi energy, and the strength of J emerge as the primary criteria for incoherent spectral response and enhanced single- and two-particle scattering that in turn controls Tc. Using c-RPA, we show further that FeSe in monolayer form (M-FeSe) provides a natural mechanism to enhance J. We explain why M-FeSe/STO has a high Tc, whereas M-FeSe in isolation should not. Our study opens a paradigm for a unified understanding what controls Tc in bulk, layers, and interfaces of Hund’s metals by hole pocket and electron screening cloud engineering.