Synopsis: Putting the squeeze on bilayer graphene

Measurements of the charge carrier response of suspended bilayer graphene flakes help identify which theoretical picture best describes the material at zero field.
Synopsis figure
Credit: J. Martin et al., Phys. Rev. Lett. (2010)

Bilayer graphene consists of two graphene sheets stacked on top of each other. In this form of graphene, the presence of collective many-body effects leads to new physics—different from that of single-layer graphene or other two-dimensional electron gas systems.

Theory predicts several phases with broken symmetry for bilayer graphene at zero magnetic field, including spontaneous charge transfer between layers, nematic ordering, ferroelectric domains, and an anomalous quantum Hall state. Not all of these phases are consistent with bilayer graphene having an energy gap at zero magnetic field, so showing the gap exists would rule out some of the possibilities.

Writing in Physical Review Letters, Jens Martin and colleagues at Harvard University probe the charge carriers in a suspended flake of bilayer graphene with a scanning single-electron transistor. They measure the electric incompressibility of the graphene, defined as the change in chemical potential with charge carrier density. From this, they find that the quantum Hall energy gaps do not vanish at zero field, but instead merge into an incompressible region near the charge neutrality point, indicating the presence of an ordered state. Martin et al.’s measurements narrow down the possible description of graphene to either an anomalous quantum Hall state or a nematic phase, though further studies will be needed to choose between the two. – Daniel Ucko


Features

More Features »

Announcements

More Announcements »

Subject Areas

Graphene

Previous Synopsis

Atomic and Molecular Physics

Wind blowing over an ultracold sea

Read More »

Next Synopsis

Related Articles

Synopsis: Graphene Helps Catch Light Quanta
Graphene

Synopsis: Graphene Helps Catch Light Quanta

The use of graphene in a single-photon detector makes it dramatically more sensitive to low-frequency light. Read More »

Focus: Graphene Sliding on Graphene
Mechanics

Focus: Graphene Sliding on Graphene

Creating a bulge in a graphene sheet offers the first measurement of the shear forces between graphene layers, an essential factor in many graphene-based devices. Read More »

Synopsis: Crumpled Graphene
Graphene

Synopsis: Crumpled Graphene

The crumpling of graphene sheets explains a “soft spot” in the material’s mechanical response. Read More »

More Articles