Imaging magnetic polarons in the doped Fermi-Hubbard model
Imaging magnetic polarons in the doped Fermi-Hubbard model
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DOI：
10.1038/s41586-019-1463-1
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发表时间：
2019-08-15
期刊：
影响因子：
64.8
通讯作者：
Gross, Christian
中科院分区：
文献类型：
--
作者：
Koepsell, Joannis;Vijayan, Jayadev;Gross, Christian
极化子——被背景环境的局部极化“装扮”的电子载流子——是相互作用的多体系统中最基本的准粒子之一，甚至在单一掺杂物的水平上也会出现(1)。在二维费米-哈伯德模型的背景下，极化子被预测在低掺杂状态下的反铁磁背景下在带电掺杂周围形成，接近莫特绝缘状态（2-7）；这一预测得到了与高温超导相关材料的宏观输运和光谱测量的支持(8)。然而，缺乏对磁极化子内部结构的直接实验观察。在这里，我们报告了掺杂费米-哈伯德系统中磁性极化子的微观实空间表征，这是由我们的超冷原子量子模拟器的单点自旋和密度分辨率实现的。我们揭示了由系统中动能和磁能之间的竞争引起的磁相关的局部约化甚至符号反转对双元的修饰。实验观察到的极化子特征与有限温度下的有效弦模型一致(7)。我们证明了双龙的离域是极化子形成的必要条件，通过将这种设置与双龙固定在晶格位置的场景进行比较。我们的工作可以促进极化子之间相互作用的研究，这可能导致集体行为，如条纹形成，以及对赝隙和“坏金属”相中极化子命运的微观探索。
Polarons-electronic charge carriers 'dressed' by a local polarization of the background environment-are among the most fundamental quasiparticles in interacting many-body systems, and emerge even at the level of a single dopant(1). In the context of the two-dimensional Fermi-Hubbard model, polarons are predicted to form around charged dopants in an antiferromagnetic background in the low-doping regime, close to the Mott insulating state(2-7); this prediction is supported by macroscopic transport and spectroscopy measurements in materials related to high-temperature superconductivity(8). Nonetheless, a direct experimental observation of the internal structure of magnetic polarons is lacking. Here we report the microscopic real-space characterization of magnetic polarons in a doped Fermi-Hubbard system, enabled by the single-site spin and density resolution of our ultracold-atom quantum simulator. We reveal the dressing of doublons by a local reduction-and even sign reversal-of magnetic correlations, which originates from the competition between kinetic and magnetic energy in the system. The experimentally observed polaron signatures are found to be consistent with an effective string model at finite temperature(7). We demonstrate that delocalization of the doublon is a necessary condition for polaron formation, by comparing this setting with a scenario in which a doublon is pinned to a lattice site. Our work could facilitate the study of interactions between polarons, which may lead to collective behaviour, such as stripe formation, as well as the microscopic exploration of the fate of polarons in the pseudogap and 'bad metal' phases.