Imaging the quantum melting of Wigner crystal with electronic quasicrystal order

TL;DR

This study visualizes the quantum melting of a Wigner crystal into a Wigner quasicrystal using STM in a moire heterostructure, revealing intermediate liquid-like phases and confirming theoretical predictions about quantum phase transitions.

Contribution

First direct visualization of quantum melting of Wigner crystal into a Wigner quasicrystal in a moire heterostructure, demonstrating the interplay of moire potential and ionic potential.

Findings

Observation of Wigner crystal melting into a quasicrystal at the quantum critical point

Identification of liquid-like characteristics during the melting process

Verification of theoretical predictions about quantum solid-liquid transitions

Abstract

Wigner crystal, as the most fundamental exemplification where the many-body interaction forges the electrons into a solid, experiences an intriguing quantum melting where diverse intermediate phases are predicted to emerge near the quantum critical point. Indications of exotic Wigner orders like bubble phase, liquid-solid phase, and anisotropic Wigner phase have been established by optical or transport measurements. However, the direct visualization of lattice-scale melting order, which is of paramount importance to unequivocally uncover the melting nature, remains challenging and lacking. Noting that Wigner crystals have been achieved in the fractionally filled moire superlattice recently, here, via scanning tunneling microscope, we image the quantum melting of Wigner solid realized by further varying the moire superstructure in monolayer YbCl3/graphene heterostructure. The Wigner solid is constructed on the two-dimensional ensemble of interfacial electron-hole pairs derived from charge transfer. The interplay between certain moire potential and ionic potential leads to the quantum melting of Wigner solid evidenced by the emergence of electron-liquid characteristic, verifying the theoretical predictions. Particularly, akin to the classical quasicrystal made of atoms, a dodecagonal quasicrystal made of electrons, i.e., the Wigner quasicrytal, is visualized at the quantum melting point. In stark contrast to the incompressible Wigner solid, the Wigner quasicrytal hosts considerable liquefied nature unraveled by the interference ripples caused by scattering. By virtue of the two-dimensional charge transfer interface composed of monolayer heavy electron material and graphene, our discovery not only enriches the exploration and understanding of quantum solid-liquid melting, but also paves the way to directly probe the quantum critical order of correlated many-body system.