Hossain Md S, Ma M K, Villegas-Rosales K A, Chung Y J, Pfeiffer L N, West K W, Baldwin K W, Shayegan M
Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA.
Phys Rev Lett. 2022 Jul 15;129(3):036601. doi: 10.1103/PhysRevLett.129.036601.
The interplay between the Fermi sea anisotropy, electron-electron interaction, and localization phenomena can give rise to exotic many-body phases. An exciting example is an anisotropic two-dimensional (2D) Wigner solid (WS), where electrons form an ordered array with an anisotropic lattice structure. Such a state has eluded experiments up to now as its realization is extremely demanding: First, a WS entails very low densities where the Coulomb interaction dominates over the kinetic (Fermi) energy. Attaining such low densities while keeping the disorder low is very challenging. Second, the low-density requirement has to be fulfilled in a material that hosts an anisotropic Fermi sea. Here, we report transport measurements in a clean (low-disorder) 2D electron system with anisotropic effective mass and Fermi sea. The data reveal that at extremely low electron densities, when the r_{s} parameter, the ratio of the Coulomb to the Fermi energy, exceeds ≃38, the current-voltage characteristics become strongly nonlinear at small dc biases. Several key features of the nonlinear characteristics, including their anisotropic voltage thresholds, are consistent with the formation of a disordered, anisotropic WS pinned by the ubiquitous disorder potential.
费米海各向异性、电子-电子相互作用和局域化现象之间的相互作用能够产生奇异的多体相。一个令人兴奋的例子是各向异性二维维格纳晶体（WS），其中电子形成具有各向异性晶格结构的有序阵列。到目前为止，这种状态一直未被实验观测到，因为其实现条件极为苛刻：首先，维格纳晶体需要极低的密度，此时库仑相互作用主导动能（费米能）。在保持低无序度的同时达到如此低的密度极具挑战性。其次，低密度要求必须在具有各向异性费米海的材料中实现。在此，我们报告了在具有各向异性有效质量和费米海的清洁（低无序）二维电子系统中的输运测量。数据表明，在极低的电子密度下，当库仑能与费米能之比的r_s参数超过约38时，在小直流偏压下电流-电压特性变得强烈非线性。非线性特性的几个关键特征，包括其各向异性电压阈值，与由普遍存在的无序势钉扎的无序、各向异性维格纳晶体的形成相一致。
