Synopsis: Watching Electrons Shake Down a Lattice

Ultrafast electron diffraction experiments probe, in real time, how electrons couple to lattice vibrations in graphite.
Synopsis figure
Mark Stern/McGill University

As electrons travel through a solid they can scatter off the atomic lattice, interacting with its vibrations (phonons). Such “electron-phonon coupling” can govern the conduction of electrons in solids and is responsible for phenomena like superconductivity. But experiments that can selectively probe electron-phonon coupling, which occurs on extremely fast timescales, are hard to realize. A team led by Bradley Siwick at McGill University, Canada, has now used a high-speed electron diffraction technique to capture the motion of a graphite lattice as it interacts with optically excited electrons.

The experiments were made possible by a pulsed electron source recently developed by the authors, in which radiofrequency fields pack electrons into short bunches of about 100 femtoseconds (fs). After laser pulses excited electrons in graphite, the authors imaged the ensuing lattice motions by observing how the crystal diffracted the electron pulse. They monitored several diffraction peaks, whose positions and intensities shifted as the lattice vibrated. The analysis shows that within 500fs of optical excitation most of the electron energy is transferred selectively to two vibrational modes, and that the initial electronic excitation produces coherent waves of lattice motion that shear the graphite planes. After a few picoseconds, this energy is redistributed over all lattice vibrations.

The ability to observe how electrons lose energy to specific phonons will help researchers assess the potential for electronic applications of a wide class of materials, including many carbon-based materials similar to graphite (such as graphene and carbon nanotubes), in which electron-phonon coupling is thought to pose the ultimate limit to carrier mobility.

This research is published in Physical Review Letters.

–Matteo Rini


Features

More Features »

Announcements

More Announcements »

Subject Areas

Materials Science

Previous Synopsis

Materials Science

More Catalysis with Less Platinum

Read More »

Next Synopsis

Related Articles

Viewpoint: Pushing Towards Room-Temperature Superconductivity
Condensed Matter Physics

Viewpoint: Pushing Towards Room-Temperature Superconductivity

Two independent studies report superconductivity at record high temperatures in hydrogen-rich materials under extreme pressure. Read More »

Focus: <i>Video</i>—Slow-Motion Footage Captures Rubber Band Ripples
Mechanics

Focus: Video—Slow-Motion Footage Captures Rubber Band Ripples

Videos of a moving rubber band show that the band takes on previously unpredicted wavy shapes when it is shot through the air. Read More »

Focus: A Home for Helium inside Earth
Materials Science

Focus: A Home for Helium inside Earth

Computations predict the existence of a compound that could store the primordial helium that is known to be present somewhere inside the Earth. Read More »

More Articles