Electronic compressibility of layer polarized bilayer graphene

TL;DR

This study uses capacitance measurements to explore how electronic compressibility in bilayer graphene varies with carrier density, temperature, and electric displacement, revealing localized states, intrinsic band gap effects, and van Hove singularities.

Contribution

It provides new insights into the electronic compressibility and layer polarization effects in bilayer graphene under different electrical displacements.

Findings

Compressibility minimum at charge neutrality deepens with increasing D.

Localized states persist within the induced band gap.

Van Hove singularities appear at band edges, showing electron-hole asymmetry.

Abstract

We report on a capacitance study of dual gated bilayer graphene. The measured capacitance allows us to probe the electronic compressibility as a function of carrier density, temperature, and applied perpendicular electrical displacement D. As a band gap is induced with increasing D, the compressibility minimum at charge neutrality becomes deeper but remains finite, suggesting the presence of localized states within the energy gap. Temperature dependent capacitance measurements show that compressibility is sensitive to the intrinsic band gap. For large displacements, an additional peak appears in the compressibility as a function of density, corresponding to the presence of a 1-dimensional van Hove singularity (vHs) at the band edge arising from the quartic bilayer graphene band structure. For D > 0, the additional peak is observed only for electrons, while D < 0 the peak appears only for holes. This asymmetry that can be understood in terms of the finite interlayer separation and may be useful as a direct probe of the layer polarization.