New Laser Images Quantum World Faster

Ultrafast pulses of ultraviolet light in a gas jet are visible as blue dots on a phosphor screen. (Source: UBC)

For the first time, researchers have been able to record, frame-by-frame, how an electron interacts with certain atomic vibrations in a solid. The technique captures a process that commonly causes electrical resistance in materials while, in others, can cause the exact opposite—the absence of resistance, or super­conductivity. “The way electrons interact with each other and their micro­scopic environment determines the properties of all solids,” said MengXing Na, a University of British Columbia PhD student. “Once we identify the dominant micro­scopic inter­actions that define a material’s properties, we can find ways to ‘turn up’ or ‘down’ the interaction to elicit useful elec­tronic properties.”

Controlling these inter­actions is important for the techno­logical exploitation of quantum materials, including super­conductors, which are used in MRI machines, high-speed magnetic levi­tation trains, and could one day revo­lutionize how energy is transported. “By applying these pioneering techniques, we’re now poised to reveal the elusive mystery of high-temperature super­conductivity and many other fascinating phenomena of quantum matter.”

At tiny scales, atoms in all solids vibrate constantly. Collisions between an electron and an atom can be seen as a scattering event between the electron and a phonon. The scattering can cause the electron to change both its direction and its energy. Such electron-phonon interactions lie at the heart of many exotic phases of matter, where materials display unique properties. With the support of the Gordon and Betty Moore Founda­tion, the team at UBC’s Stewart Blusson Quantum Matter Institute (SBQMI) developed a new extreme-ultra­violet laser source to enable time-resolved photo­emission spectro­scopy for visualizing electron scattering processes at ultrafast time­scales.

“Using an ultrashort laser pulse, we excited individual electrons away from their usual equi­librium environ­ment,” said Na. “Using a second laser pulse as an effective camera shutter, we captured how the electrons scatter with surroun­ding atoms on timescales faster than a trillionth of a second. Owing to the very high sensi­tivity of our setup, we were able to measure directly for the first time how the excited electrons interacted with a specific atomic vibration, or phonon.”

The researchers performed the experiment on graphite, a crystal­line form of carbon and the parent compound of carbon nanotubes, Bucky balls and graphene. Carbon-based electronics is a growing industry, and the scattering processes that contribute to electrical resistance may limit their application in nano­electronics. The approach leverages a unique laser facility conceived by David Jones and Andrea Damas­celli, and developed by Arthur Mills, at the UBC-Moore Centre for Ultrafast Quantum Matter.

“Thanks to recent advances in pulsed-laser sources, we’re only just beginning to visualize the dynamic properties of quantum materials,” said Jones, a professor with UBC’s SBQMI and department of Physics and Astronomy. “By applying these pio­neering techniques, we’re now poised to reveal the elusive mystery of high-tempera­ture super­conductivity and many other fasci­nating phenomena of quantum matter,” said Damascelli, scientific director of SBQMI. (Source: UCB)

Reference: M. X. Na et al.: Direct determination of mode-projected electron-phonon coupling in the time domain, Science 366, 1231 (2019); DOI: 10.1126/science.aaw1662

Link: ARPES on Complex Systems, Dept. of Physics and Astronomy, University of British Columbia, Vancouver, Canada

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