Measurement of the electronic compressibility of bilayer graphene

TL;DR

This study measures the electronic compressibility of bilayer graphene under various conditions, revealing its band structure, asymmetry, and effects of electric and magnetic fields, including Landau level behavior and disorder effects.

Contribution

It provides detailed experimental data on bilayer graphene's electronic compressibility, highlighting the effects of electric fields and magnetic fields on its band structure and Landau levels.

Findings

Observation of hyperbolic band structure

Detection of band asymmetry between conduction and valence bands

Broad Landau level oscillations indicating degeneracy and disorder broadening

Abstract

We present measurements of the electronic compressibility, $K$, of bilayer graphene in both zero and finite magnetic fields up to 14 T, and as a function of both the carrier density and electric field perpendicular to the graphene sheet. The low energy hyperbolic band structure of bilayer graphene is clearly revealed in the data, as well as a sizable asymmetry between the conduction and valence bands. A sharp increase in $K^{-1}$ near zero density is observed for increasing electric field strength, signaling the controlled opening of a gap between these bands. At high magnetic fields, broad Landau level (LL) oscillations are observed, directly revealing the doubled degeneracy of the lowest LL and allowing for a determination of the disorder broadening of the levels.