近日，美国普林斯顿大学的Waseem S. Bakr及其研究团队取得一项新进展。经过不懈努力，他们在动力学阻挫的哈伯德系统中直接成像自旋极化子。相关研究成果已于2024年5月8日在国际权威学术期刊《自然》上发表。

据悉，量子多体系统中准粒子的出现是许多强相互作用材料丰富现象学的基础。在掺杂莫特绝缘体中，磁极化子通常源自掺杂载流子动能与超交换自旋相互作用之间的相互作用。然而，在动力学阻挫的晶格环境中，即使缺乏超交换耦合，理论上也预测了掺杂剂与自旋翻转流动之间形成的自旋极化子束缚态。尽管极化子在动力学磁力理论中占据重要地位，但针对这些极化子的微观观测仍显不足。

该研究团队直接成像了用超冷原子实现的三角形晶格哈伯德系统中的流动自旋极化子，揭示了在空穴掺杂剂的局部环境中增强的反铁磁关联性。相反，在电荷掺杂剂周围，研究人员发现了铁磁关联性，这是难以捉摸的Nagaoka效应的一种表现。研究人员研究了这些关联与相互作用和掺杂的演变，并利用高阶相关函数进一步阐明了超交换机制和动力学机制的相对贡献。流动自旋极化子在高温下的鲁棒性为探索阻挫体系中空穴配对和超导的潜在机制铺平了道路。此外，这项研究工作为三角晶格莫尔材料中的相关现象提供了微观见解。

附：英文原文

Title: Directly imaging spin polarons in a kinetically frustrated Hubbard system

Author: Prichard, Max L., Spar, Benjamin M., Morera, Ivan, Demler, Eugene, Yan, Zoe Z., Bakr, Waseem S.

Issue&Volume: 2024-05-08

Abstract: The emergence of quasiparticles in quantum many-body systems underlies the rich phenomenology in many strongly interacting materials. In the context of doped Mott insulators, magnetic polarons are quasiparticles that usually arise from an interplay between the kinetic energy of doped charge carriers and superexchange spin interactions. However, in kinetically frustrated lattices, itinerant spin polarons—bound states of a dopant and a spin flip—have been theoretically predicted even in the absence of superexchange coupling. Despite their important role in the theory of kinetic magnetism, a microscopic observation of these polarons is lacking. Here we directly image itinerant spin polarons in a triangular-lattice Hubbard system realized with ultracold atoms, revealing enhanced antiferromagnetic correlations in the local environment of a hole dopant. In contrast, around a charge dopant, we find ferromagnetic correlations, a manifestation of the elusive Nagaoka effect. We study the evolution of these correlations with interactions and doping, and use higher-order correlation functions to further elucidate the relative contributions of superexchange and kinetic mechanisms. The robustness of itinerant spin polarons at high temperature paves the way for exploring potential mechanisms for hole pairing and superconductivity in frustrated systems. Furthermore, our work provides microscopic insights into related phenomena in triangular-lattice moiré materials.

DOI: 10.1038/s41586-024-07356-6

Source: https://www.nature.com/articles/s41586-024-07356-6