Composite fermion liquid to Wigner solid transition in the lowest Landau level of zinc oxide

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 it is a dilute two-dimensional electron system in a magnetic field, which evolves intricately through various gaseous, liquid and solid phases governed by Coulomb interaction. Here we report on the experimental observation of a phase transition between the composite fermion liquid and adjacent magnetic field induced phase with a character of 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-like phase further into the composite fermion liquid phase region. Our observations indicate the direct competition between a composite fermion liquid and a Wigner solid formed either by electrons or composite fermions.

Thirty Years of Composite Fermions and Beyond

“…Given various approximations made in our calculation and our neglect of disorder (disorder should favor a crystal, because a crystal can more readily adjust to it than an incompressible liquid), we regard the level of agreement to be satisfactory. Similar considerations apply to ZnO quantum wells 156 for which κ is ∼ 6.4 times larger than that for n-doped GaAs systems. 105 Why does LL mixing favor the crystal phase?…”

Competing correlated states around the zero-field Wigner crystallization transition of electrons in two dimensions

“…From our experiences in higher charge density devices (n = 2 ∼ 5 × 10 11 cm −2 ) with similar geometries, such as those studied in Refs. [16,17,49], Joule heating is negligible in the analysis of fractional quantum Hall energy gaps for currents below approximately 10 nA. However, the charge density, resistivity, and proximity to the MIT of the device under study here puts it in a different parameter space, necessitating a reevaluation of the role of current-induced heating.…”

Particle-hole symmetry and the reentrant integer quantum Hall Wigner solid

“…In yet other systems, phases associated with the WS may straddle more than just one FQHS. This is the case of a 2DEG realized in the ZnO/MgZnO system in which the WS was found to straddle several FQHSs 41 . These experiments suggest that disorder influences the range of stability of the WS and highlight that there is still much to be understood about disorder effects.…”

“…While the above WSs were discovered in GaA/AlGaAs hosts, recent progress with the quality of other host materials yielded similar physics. For example, Wigner crystallization has recently been observed in the ZnO/ZnMgO system 40,41 , graphene 42 , and in AlAs quantum wells 43 .…”