New picosecond laser technique to shed light on conductivity

Canadian researchers use laser pulses to record frame-by-frame how electrons react with atomic vibrations in solids, revealing superconductivity mechanisms

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Ultrafast pulses of extreme ultraviolet light are created in a gas jet (white plasma), and are visible as blue dots on a phosphor screen as well as yellow beams from oxygen fluorescence. Credit: Research2Reality

New insights into superconductivity could be gleaned from the technique, discussed by physicists from the Stewart Blusson Quantum Matter Institute (SBQMI) at the University of British Columbia and their colleagues in Science. The researchers have developed a new extreme-ultraviolet laser source to enable a technique called time-resolved photoemission spectroscopy, which visualises how electrons are scattered from atoms in solid materials at ultrafast timescales.

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“Using an ultrashort laser pulse, we excited individual electrons away from their usual equilibrium environment,” said MengXing Na, a PhD student at SBQMI and co-lead author of the Science paper. “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.”

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MengXing Na and Andrea Damascelli at UBC’s Stewart Blusson Quantum Matter Institute (SBQMI). Credit: Research2Reality

This is significant because such interactions define the conductive properties of the material. In some, it gives rise to resistance, while in others it can cause the exact opposite: superconductivity. “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,” Na said.

The team performed their experiments on graphite, using a laser facility developed by Arthur Mills, the other co-lead author on the paper, and conceived by David Jones and Andrea Damascelli, professors at SBQMI. “Thanks to recent advances in pulsed-laser sources, we’re only just beginning to visualise the dynamic properties of quantum materials,” said Jones.

“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,” Damascelli added.