Synopsis

Charting Flatland Materials

Physics 18, s9
Researchers have measured graphene’s plasmon spectrum using a novel electron-based spectroscopy technique.
A. Guandalini et al. [1]

Light-based instruments that probe electronic quasiparticles in few-atom-thick material sheets are limited to sheets at least as large as the wavelength of light, which are not always possible to fabricate. Existing alternatives replace the light probe with an electron beam. However, this introduces changes in the material’s electron momentum, unlike light-based tests. Now Alberto Guandalini of Sapienza University of Rome, Thomas Pichler of the University of Vienna, and their collaborators have improved the energy and momentum resolution of an electron-beam-based technique and measured the plasmon energies of graphene—collective electronic oscillations in a one-atom-thick sheet of carbon atoms—at the smallest electron momentum change reported yet [1].

The technique entails directing a beam of electrons at graphene and analyzing the energy and momentum of the scattered electrons that pass through. Building on previous theories, the team identified that the measurement outcome has two contributions. One accounts for the intrinsic properties of graphene. The other, called kinematic, arises solely from momentum and energy-conservation rules. By deriving a formula for the kinematic contribution, the team isolated graphene’s intrinsic response.

To achieve a low-momentum measurement, the researchers introduced a pinhole aperture to let through only scattered electrons that experienced low momentum changes. They obtained graphene’s plasmon spectrum by repeatedly changing the energy of the incoming electron beam and accounting for kinematic effects. The high-resolution spectrum revealed that kinematic contributions dominate the signal, contrary to previous reports. The team says the improved technique can probe other few-atom-thick materials and ultrathin films at the nanoscale, and eventually it could be used to study operating devices.

–Martin Rodriguez-Vega

Martin Rodriguez-Vega is an Associate Editor for Physical Review Letters.

References

  1. A. Guandalini et al., “Direct observation of the vanishing electron energy loss spectroscopy cross section in graphene,” Phys. Rev. B 111, L041401 (2025).

Subject Areas

Condensed Matter PhysicsMaterials Science

Related Articles

Active Polymers Tie Themselves in Knots
Statistical Physics

Active Polymers Tie Themselves in Knots

Simulations show that polymers that include inert and self-propelled components are more likely to form and retain knots, with possible applications in materials engineering. Read More »

Magnetic Field Maneuvers Magnetite Monolayers
Materials Science

Magnetic Field Maneuvers Magnetite Monolayers

An external magnetic field can bend and lift thin sheets of self-assembled nanoparticles. Read More »

Chirality Switching On Demand
Topological Insulators

Chirality Switching On Demand

A device made of multilayer graphene exhibits topologically protected edge currents whose direction can be switched using an electric field. Read More »

More Articles