Signature of Correlated Insulator in Electric Field Controlled Superlattice

TL;DR

This paper reports the discovery of a correlated insulator phase in bilayer graphene modulated by a superlattice, revealing flat energy bands and electron correlations induced by nanopatterned electric gates.

Contribution

It demonstrates the emergence of a correlated insulator in a superlattice-modulated bilayer graphene, linking flat bands to electron correlations and symmetry breaking.

Findings

Signatures of correlated insulator phase at specific carrier densities

Formation of flat energy bands due to superlattice potential

Potential for designing custom superlattices for electron correlation studies

Abstract

The Bloch electron energy spectrum of a crystalline solid is determined by the underlying lattice structure at the atomic level. In a 2-dimensional (2d) crystal it is possible to impose a superlattice with nanometer-scale periodicity, allowing to tune the fundamental Bloch electron spectrum, and enabling novel physical properties which are not accessible in the original crystal. In recent years, a top-down approach for creating 2d superlattices on monolayer graphene by means of nanopatterned electric gates has been studied, which allows the formation of isolated energy bands and Hofstadter Butterfly physics in quantizing magnetic fields. Within this approach, however, evidence of electron correlations which drive many problems at the forefront of physics research remains to be uncovered. In this work we demonstrate signatures of a correlated insulator phase in Bernal-stacked bilayer graphene (BLG) modulated by a gate-defined superlattice potential, manifested as a set of resistance peaks centered at carrier densities of integer multiples of a single electron per unit cell of the superlattice potential. We associate the correlated insulator phase to the formation of flat energy bands due to the superlattice potential combined with inversion symmetry breaking. Inducing correlated electron phases with nanopatterning defined electric gates paves the way to custom-designed superlattices with arbitrary geometries and symmetries for studying band structure engineering and strongly correlated electrons in 2d materials.