Phase transition from a composite fermion liquid to a Wigner solid in the lowest Landau level of ZnO

TL;DR

This paper reports the experimental observation of a phase transition between a composite fermion liquid and a Wigner solid in a ZnO two-dimensional electron system, revealing the competition between liquid and solid phases driven by Coulomb interactions.

Contribution

First experimental evidence of a direct phase transition between Laughlin liquid and Wigner solid in the lowest Landau level of ZnO, highlighting composite particles' role.

Findings

Observation of a phase transition between Laughlin liquid and Wigner solid.

Extension of the Wigner phase into the liquid region with in-plane magnetic field.

Evidence of competition between composite fermion liquid and Wigner solid.

Abstract

Interactions between the constituents of a condensed matter system can drive it through a plethora of different phases due to many-body effects. A prominent platform for this type of behavior is a two-dimensional electron system in a magnetic field, which evolves intricately through various gaseous, liquid and solids phases governed by Coulomb interaction. Here we report on the experimental observation of a phase transition between the Laughlin liquid of composite fermions and the adjacent insulating phase of a magnetic field-induced Wigner solid. The experiments are performed in the lowest Landau level of a MgZnO/ZnO two-dimensional electron system with attributes of both a liquid and a solid. An in-plane magnetic field component applied on top of the perpendicular magnetic field extends the Wigner phase further into the liquid phase region. Our observations indicate the direct competition between a Wigner solid and a Laughlin liquid both formed by composite particles rather than bare electrons.