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1934年，就读于普林斯顿大学的Eugene Wigner预言了电子晶体的存在。电子同时具有动能和相互作用的势能，在电子态密度满足一定的条件时，由于电子之间的排斥作用，电子会倾向于按规则的晶格结构排布，形成电子晶体，也称为维格纳晶体。近90年来，维格纳晶体一直吸引着凝聚态物理学家。1979年，实验发现在液氦表面存在着从电子液体到电子晶体相变的现象，之后的实验在强磁场下的二维电子气中观察到二维维格纳晶体的特征。然而，在实空间中直接观测二维维格纳晶格仍然是一项艰巨的挑战。通过WSe2/WS2moiré超晶格的石墨烯传感层， Hongyuan Li和Wang Feng等人在实验中观察到了维格纳晶体的实空间形貌。而在最近的研究中，研究人员使用高分辨率扫描隧道显微镜测量技术，直接对贝纳尔堆叠（bernal stacking）双层石墨烯中的磁场诱导维格纳晶体进行成像，并研究其结构特性与电子密度、磁场和温度的函数关系。本文将通过四篇代表性工作，简要介绍维格纳晶体的进展和发展前景。In 1934, Eugene Wigner, who attended Princeton University, predicted the existence of electronic crystals. Electrons have both kinetic energy and potential energy of interaction. When the density of electronic states satisfies certain conditions, due to the repulsion between electrons, electrons will tend to arrange themselves in a regular lattice structure, forming electron crystals, also known as Wigner crystals. For nearly 90 years, Wigner crystals have fascinated condensed matter physicists. Physicists have designed many ingenious semiconductor heterojunctions to obtain lower electron densities and added magnetic fields to obtain larger effective masses of electrons.In 1979, experiments revealed the existence of a phase transition from an electron liquid phase to an electron crystal on the surface of liquid helium, and subsequent experiments observed the characteristics of two-dimensional Wigner crystals in two-dimensional electron gas at high magnetic fields. However, direct observation of 2D Wigner lattices in real space remains a formidable challenge. Through the graphene sensing layer of WSe2/WS2moiré superlattice, Hongyuan Li and Wang Feng et al. observed the real-space morphology of Wigner crystals in their experiments. And in a recent study, researchers used high-resolution scanning tunneling microscopy measurements to directly image magnetic field-induced Wigner crystals in bernal stacking bilayer graphene and investigate their structural properties as a function of electron density, magnetic field, and temperature. In this paper, we will introduce some interesting things about Wigner crystals through four representative works briefly.
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Keywords:
- Wigner crystals /
- electron solids /
- quantum phase transitions /
- scanning tunneling microscopy
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