Ultrafast imaging of electron waves in graphene

Celia Elliott
11/5/2010

The fastest movies ever made of electron motion, created by scattering x-rays off of graphene, have shown that the interaction among its electrons is surprisingly weak.

Graphene is a single atomic layer of carbon whose unusual electronic structure makes it a candidate for a new generation of low-cost, flexible electronics. A major outstanding question is whether the electrons in graphene move independently, or if their motion is correlated by Coulomb repulsion.

Using advanced x-ray scattering techniques, physicists in Peter Abbamonte’s group at the University of Illinois at Urbana-Champaign have imaged the motion of electrons in graphene with resolutions of 0.533 Å and 10.3 attoseconds. Their results were published on November 5 in Science.

Exactly how small and how fast are these measurements? An angstrom is 1/10,000,000,000 of a meter, about the width of a hydrogen atom. And an attosecond is to a second as a second is to the age of the universe.

The researchers found that graphene screens Coulomb interactions surprisingly effectively, causing it to act like a simple, independent-electron semimetal. Their work explains several mysteries, including why freestanding graphene fails to become an insulator as predicted. The study also demonstrates a new approach to studying ultrafast dynamics, creating a new window on the most fundamental properties of materials.

The experiments were carried out at the Frederick Seitz Materials Research Laboratory at the University of Illinois and the Advanced Photon Source at Argonne National Laboratory.

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Scientists at the University of Illinois at Urbana-Champaign working in dark matter research have gotten together and planned a celebration of Dark Matter Day (October 31), just a few days early. A free screening of the visually stunning documentary, Seeing the Beginning of Time, will take place at the National Center for Supercomputing Applications (NCSA) on October 24, 2017, at 7 p.m., followed by a Q&A session with a panel of experts. This event is open to all, though seating is limited.

Seeing the Beginning of Time is a 50-minute visually stunning journey through deep space and time, co-produced by the NCSA, and Thomas Lucas Productions. The trailer is viewable on YouTube at https://www.youtube.com/watch?time_continue=3&v=5P0vfe5dC5A.

The American Chemical Society (ACS), through its Division of History of Chemistry, has an award that acknowledges these greatest of strides: the Chemical Breakthrough Awards are presented annually in recognition of “seminal chemistry publications, books, and patents that have been revolutionary in concept, broad in scope, and long-term in impact.” These awards are made to the department where the breakthrough occurred, not to the individual scientists or inventors.

This year, the ACS honored the discovery of “J-coupling” (also known as spin-spin coupling) in liquids, a breakthrough that enabled scientists to use Nuclear Magnetic Resonance (NMR) spectroscopy to identify atoms that are joined by a chemical bond and so to determine the structure of molecules.

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Today’s historic joint announcement by the U.S.-based Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Europe-based Virgo detector of the first detection of gravitational waves produced by colliding neutron stars is doubly noteworthy. It’s also the first cosmic event observed in both gravitational waves and light—some 70 ground- and space-based observatories observed the colliding neutron stars. This is arguably the biggest moment to date in “multi-messenger astronomy.”

In a press release issued by LIGO and Virgo collaborations, National Science Foundation Director France A. Córdova comments, “It is tremendously exciting to experience a rare event that transforms our understanding of the workings of the universe. This discovery realizes a long-standing goal many of us have had, that is, to simultaneously observe rare cosmic events using both traditional as well as gravitational-wave observatories. Only through NSF’s four-decade investment in gravitational-wave observatories, coupled with telescopes that observe from radio to gamma-ray wavelengths, are we able to expand our opportunities to detect new cosmic phenomena and piece together a fresh narrative of the physics of stars in their death throes.”

Well before the development of today’s innovative technologies supporting this simultaneous gravitational-wave and optical observation, early research in numerical relativity at the University of Illinois at Urbana-Champaign helped to lay the theoretical foundation for it. In fact, many features of the discovery had been predicted in the early computational simulations of Professor of Physics and Astronomy Stuart Shapiro and his group.

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A team of scientists using the Dark Energy Camera (DECam), the primary observing tool of the Dark Energy Survey (DES), was among the first to observe the fiery aftermath of a recently detected burst of gravitational waves, recording images of the first confirmed explosion from two colliding neutron stars ever seen by astronomers.

Scientists on the DES joined forces with a team of astronomers based at the Harvard-Smithsonian Center for Astrophysics (CfA) for this effort, working with observatories around the world to bolster the original data from DECam. Images taken with DECam captured the flaring-up and fading over time of a kilonova – an explosion similar to a supernova, but on a smaller scale – that occurs when collapsed stars (called neutron stars) crash into each other, creating heavy radioactive elements.

Two scientists at the University of Illinois at Urbana-Champaign are members of the DES collaboration, Professors Joaquin Vieira of the Departments of Astronomy and of Physics and Felipe Menanteau of the Department