近日，澳大利亚斯威本科技大学的Xia-Ji Liu及其研究团队取得一项新进展。经过不懈努力，他们对二维方形晶格中的超级费米极化子和Nagaoka铁磁性进行研究。相关研究成果已于2024年8月13日在国际知名学术期刊《物理评论A》上发表。

该研究团队研究了杂质在二维方形晶格点阵中跳跃并与给定填充因子下的大量费米子相互作用所形成的费米极化子问题。当相互作用为吸引性时，研究人员发现了标准的费米极化子准粒子，它们被归类为吸引性极化子和排斥性极化子。有趣的是，当相互作用变为排斥性时，研究人员观察到了一个非常规的高度激发态极化子准粒子，其在第一布里渊区角动量K=(±π,±π)处呈现尖锐峰值。这种超费米极化子分支的产生是由于杂质运动与费米子空穴而非粒子的结合。

研究发现，随着杂质-费米子排斥作用的增强，超费米极化子的定义越来越明确，并且可能被视为Nagaoka铁磁性的前驱体，后者将在足够大的排斥作用和较大的填充因子下出现。此外，他们还研究了超费米极化子的温度依赖性，并发现它们在温度显著升高时具有热稳定性。

附：英文原文

Title: Super Fermi polaron and Nagaoka ferromagnetism in a two-dimensional square lattice

Author: Hui Hu, Jia Wang, Xia-Ji Liu

Issue&Volume: 2024/08/13

Abstract: We consider the Fermi polaron problem of an impurity hopping around a two-dimensional square lattice and interacting with a sea of fermions at given filling factor. When the interaction is attractive, we find standard Fermi polaron quasiparticles, categorized as attractive polarons and repulsive polarons. When the interaction becomes repulsive, interestingly, we observe an unconventional highly excited polaron quasiparticle, sharply peaked at the corner of the first Brillouin zone with momentum K=(±π,±π). This super Fermi polaron branch arises from the dressing of the impurity's motion with holes, instead of particles of fermions. We show that super Fermi polarons become increasingly well defined with increasing impurity-fermion repulsions and might be considered as a precursor of Nagaoka ferromagnetism, which would appear at sufficiently large repulsions and at large filling factors. We also investigate the temperature dependence of super Fermi polarons and find that they are thermally robust against the significant increase in temperature.

DOI: 10.1103/PhysRevA.110.023314

Source: https://journals.aps.org/pra/abstract/10.1103/PhysRevA.110.023314