韩国延世大学Keun Su Kim研究小组在二维偶极子液体中观察到电子旋子和维格纳晶体。相关论文于2024年10月16日发表在《自然》杂志上。

据了解，朗道提出的解释超流体液氦的一个关键概念是量子粒子的基本激发，称为旋子。液体中原子的不规则排列导致了旋子的非周期色散，这在理解分数量子霍尔液体（磁旋子）和玻色-爱因斯坦凝聚态的超固态中发挥了关键作用。即使对于二维电子或偶极子液体，在没有磁场的情况下，排斥性相互作用也被预测会形成旋子最小值，这可以追溯到维格纳晶体和超导的转变，尽管这还没有被观察到。

课题组报道了在碱金属离子的二维偶极子液体中观察到的这种电子旋子，它们向黑磷表层提供电子。他们的数据揭示了惊人的旋子非周期色散，其特征是有限动量下的局部能量最小。随着偶极子密度的降低，相互作用超过了动能，旋子间隙减小到0，就像在晶体中一样，这是维格纳结晶的信号。

他们的模型显示了由偶极子之间的斥力引起的短程有序的重要性，这可以看作是漂浮在费米液体海洋中的维格纳晶体（气泡或条纹）的形成。他们的结果揭示了电子旋子（和赝隙）的主要起源是强相关性。

附：英文原文

Title: Electronic rotons and Wigner crystallites in a two-dimensional dipole liquid

Author: Park, Soobin, Huh, Minjae, Jozwiak, Chris, Rotenberg, Eli, Bostwick, Aaron, Kim, Keun Su

Issue&Volume: 2024-10-16

Abstract: A key concept proposed by Landau to explain superfluid liquid helium is the elementary excitation of quantum particles called rotons1,2,3,4,5,6,7,8. The irregular arrangement of atoms in a liquid leads to the aperiodic dispersion of rotons, which played a pivotal role in understanding fractional quantum Hall liquids (magneto-rotons)9,10 and the supersolidity of Bose–Einstein condensates11,12,13. Even for a two-dimensional electron or dipole liquid, in the absence of a magnetic field, the repulsive interactions have been predicted to form a roton minimum14,15,16,17,18,19, which can be used to trace the transition to Wigner crystals20,21,22,23,24 and superconductivity25,26,27, although this has not yet been observed. Here, we report the observation of such electronic rotons in a two-dimensional dipole liquid of alkali-metal ions donating electrons to surface layers of black phosphorus. Our data reveal the striking aperiodic dispersion of rotons, which is characterized by a local minimum of energy at finite momentum. As the density of dipoles decreases so that interactions dominate over the kinetic energy, the roton gap reduces to 0, as in a crystal, signalling Wigner crystallization. Our model shows the importance of short-range order arising from repulsion between dipoles, which can be viewed as the formation of Wigner crystallites (bubbles or stripes) floating in the sea of a Fermi liquid. Our results reveal that the primary origin of electronic rotons (and the pseudogap) is strong correlations.

DOI: 10.1038/s41586-024-08045-0

Source: https://www.nature.com/articles/s41586-024-08045-0