Spectroscopic signatures of many-body correlations in magic-angle twisted bilayer graphene
Spectroscopic signatures of many-body correlations in magic-angle twisted bilayer graphene
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DOI：
10.1038/s41586-019-1422-x
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发表时间：
2019-08-01
期刊：
影响因子：
64.8
通讯作者：
Yazdani, Ali
中科院分区：
文献类型：
--
作者：
Xie, Yonglong;Lian, Biao;Yazdani, Ali
磁力扭曲双层石墨烯 (MATBG)(1,2) 中超导和绝缘态的发现激发了人们对了解这种化学原始材料中电子相互作用本质的极大兴趣。 MATBG 的输运特性随掺杂变化而变化，与高转变温度氧化铜和其他非常规超导体 (1-3) 相似，这表明 MATBG 可能是一个高度相互作用的系统。然而，据我们所知，没有直接的实验证据表明 MATBG 具有很强的多体相关性。在这里，我们展示了使用扫描隧道显微镜获得的高分辨率光谱测量，这些测量提供了作为载流子密度函数的证据。 MATBG 显示出不寻常的光谱特征，这可归因于各种掺杂水平上的电子-电子相互作用，包括在该系统中出现超导性的水平。我们表明，我们的测量结果无法用在 MATBG 中模拟电子-电子相互作用的平均场方法来解释。平均场方法在应用于其他相关超导体（例如氧化铜）时的崩溃长期以来一直激发了对高度相关哈伯德模型（3）的研究。我们证明，现象学扩展哈伯德模型簇计算是由 MATBG 相关电子态的近局域性质驱动的，产生与我们实验观察到的光谱特征相似的光谱特征。我们的研究结果证明了多体相关性在理解 MATBG 特性方面的关键作用。
The discovery of superconducting and insulating states in magi-cangle twisted bilayer graphene (MATBG)(1,2) has ignited considerable interest in understanding the nature of electronic interactions in this chemically pristine material. The transport properties of MATBG as a function of doping are similar to those of high-transition-temperature copper oxides and other unconventional superconductors(1-3), which suggests that MATBG may be a highly interacting system. However, to our knowledge, there is no direct experimental evidence of strong many-body correlations in MATBG. Here we present high-resolution spectroscopic measurements, obtained using a scanning tunnelling microscope, that provide such evidence as a function of carrier density. MATBG displays unusual spectroscopic characteristics that can be attributed to electron-electron interactions over a wide range of doping levels, including those at which superconductivity emerges in this system. We show that our measurements cannot be explained with a mean-field approach for modelling electron-electron interactions in MATBG. The breakdown of a mean-field approach when applied to other correlated superconductors, such as copper oxides, has long inspired the study of the highly correlated Hubbard model(3). We show that a phenomenological extended-Hubbard-model cluster calculation, which is motivated by the nearly localized nature of the relevant electronic states of MATBG, produces spectroscopic features that are similar to those that we observed experimentally. Our findings demonstrate the critical role of many-body correlations in understanding the properties of MATBG.