Visualizing 1D zigzag Wigner crystallization at domain walls in the Mott insulator TaS$_2$

TL;DR

This study directly images a 1D Wigner crystal in the Mott insulator TaS$_2$ using STM, revealing charge ordering at higher temperatures due to strong Coulomb interactions and low electron density.

Contribution

It provides the first direct visualization of 1D Wigner crystallization in a Mott insulator, demonstrating the role of domain walls and band bending in facilitating charge order.

Findings

Observation of zigzag charge patterns consistent with Wigner crystal formation

Charge and spin fluctuations detected via noise signatures

Wigner crystal stability at higher temperatures due to Coulomb energy scales

Abstract

In a certain regime of low carrier densities and strong correlations, electrons can crystallize into a periodic arrangement of charge known as Wigner crystal. Such phases are particularly interesting in one dimension (1D) as they display a variety of charge and spin ground states which may be harnessed in quantum devices as high-fidelity transmitters of spin information. Recent theoretical studies suggest that the strong Coulomb interactions in Mott insulators and other flat band systems, may provide an attractive higher temperature platform for Wigner crystallization, but due to materials and device constraints experimental realization has proven difficult. In this work we use scanning tunneling microscopy at liquid helium temperatures to directly image the formation of a 1D Wigner crystal in a Mott insulator, TaS$_2$. Charge density wave domain walls in TaS$_2$ create band bending and provide ideal conditions of low densities and strong interactions in 1D. STM spectroscopic maps show that once the lower Hubbard band crosses the Fermi energy, the charges rearrange to minimize Coulomb energy, forming zigzag patterns expected for a 1D Wigner crystal. The zigzag charge patterns show characteristic noise signatures signifying charge or spin fluctuations induced by the tunneling electrons, which is expected for this more fragile condensed state. The observation of a Wigner crystal at orders of magnitude higher temperatures enabled by the large Coulomb energy scales combined with the low density of electrons, makes TaS$_2$ a promising system for exploiting the charge and spin order in 1D Wigner crystals.