Cascade of strongly correlated quantum states in a partially filled kagome flat band

Caiyun Chen, Jiangchang Zheng, Yuman He, Xuzhe Ying, Soumya Sankar, Luanjing Li, Yizhou Wei, Xi Dai, Hoi Chun Po, Berthold Jäck
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Abstract

Coulomb interactions among charge carriers that occupy an electronic flat band have a profound impact on the macroscopic properties of materials. At sufficient strength, these interactions can give rise to captivating phenomena such as quantum criticality, Mott-Hubbard states, and unconventional superconductivity. The appearance of these characteristics sensitively depends on the number of electrons occupying the flat band states. In this work, we present experimental evidence obtained from scanning tunneling microscopy measurements for a cascade of strongly correlated states appearing in the partially occupied kagome flat bands of Co$_{1-x}$Fe$_x$Sn whose filling can be controlled by the Fe-doping level $x$. At elevated temperatures ($T\geq16\,K$), we detect a nematic electronic state across a broad doping range $0.05100\,$meV) blend the states of two $3d$-orbital derived flat bands and impart a nematic order parameter. This state serves as the parent phase of a strongly correlated phase diagram: At lower temperatures $T<16\,$K, we find spectroscopic evidence for an orbital-selective Mott state enabled by the $3d$-orbital degeneracy of the Co atom. This state can only be detected in samples with ideal Fe doping ($x=0.17$) and descends into pseudogap phases upon electron and hole doping. At $T<8\,$K, the pseudogap phase evolves into another nematic low temperature state. Our observations demonstrate that the electronic ground state of a kagome flat band depends on the complex interplay between strong Coulomb repulsion, $3d$-orbital degeneracy, and flat band filling fraction at different temperatures.
部分填充的神户平带中的强相关量子态级联
占据电子平带的电荷载流子之间的库仑相互作用对材料的宏观特性有着深远的影响。在强度足够的情况下,这些相互作用会产生迷人的现象,如量子临界、莫特-哈伯德态和非常规超导。这些特性的出现敏感地取决于占据平带态的电子数量。在这项工作中,我们提出了通过扫描隧道显微镜测量获得的实验证据,证明在 Co$_{1-x}$Fe$_x$Sn 的部分占据的卡戈米扁带中出现了一连串强相关态,其填充可由铁掺杂水平 x$ 控制。在高温($T\geq16\,K$)条件下,我们检测到一种向列电子态,它在很宽的掺杂范围内($0.05100\,$meV)混合了两个 3d$ 轨道衍生的平坦带状态,并形成了一个向列有序参数。这种状态是强相关相图的母相:在较低的温度$T<16,$K下,我们发现了由钴原子的$3d$轨道退化性促成的轨道选择性莫特态的光谱证据。这种状态只能在掺入理想铁元素(x=0.17)的样品中检测到,并在掺入电子和空穴后进入伪缺口阶段。在$T<8\,$K时,伪电位态演变为另一低温态。我们的观察结果表明,在不同温度下,卡戈美平带的电子地态取决于强库仑斥力、3d$轨道退化和平带填充率之间复杂的相互作用。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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