Tunable Moir\'e Bands and Strong Correlations in Small-Twist-Angle Bilayer Graphene

TL;DR

This paper explores how small-twist-angle bilayer graphene exhibits unique electronic properties, including moiré patterns, strong correlations, and Hofstadter butterfly spectra, revealing new quantum phenomena driven by electron interactions.

Contribution

It provides experimental evidence of tunable moiré bands and strong correlation effects in bilayer graphene with twist angles below 1 degree, advancing understanding of moiré physics.

Findings

Observation of conductivity minima at charge neutrality

Detection of satellite gaps at specific carrier densities

Emergence of Hofstadter butterfly and broken symmetry quantum Hall states

Abstract

According to electronic structure theory, bilayer graphene is expected to have anomalous electronic properties when it has long-period moir\'e patterns produced by small misalignments between its individual layer honeycomb lattices. We have realized bilayer graphene moir\'e crystals with accurately controlled twist angles smaller than 1 degree and studied their properties using scanning probe microscopy and electron transport. We observe conductivity minima at charge neutrality, satellite gaps that appear at anomalous carrier densities for twist angles smaller than 1 degree, and tunneling densities-of-states that are strongly dependent on carrier density. These features are robust up to large transverse electric fields. In perpendicular magnetic fields, we observe the emergence of a Hofstadter butterfly in the energy spectrum, with four-fold degenerate Landau levels, and broken symmetry quantum Hall states at filling factors 1, 2, 3. These observations demonstrate that at small twist angles, the electronic properties of bilayer graphene moir\'e crystals are strongly altered by electron-electron interactions.