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Imagine being able to tune the properties of a solid material just by flashing pulses of light on it, for example turning an insulator into a superconductor. That is just one potential payoff down-the-road from the physical phenomenon of electrons and atoms interacting with ultrashort pulses of light. The technology of ultrafast spectroscopy is a key to understanding this phenomenon and now a new wrinkle to that technology has been introduced by Berkeley Lab researchers.

In a study led by Alessandra Lanzara of Berkeley Lab’s Materials Sciences Division, time- and angle-resolved photoemission spectroscopy (trARPES) was used to directly measure the ultrafast response of electron self-energy—a fundamental quantity used to describe “many-body” interactions in a material—to photo-excitation with near-infrared light in a high-temperature superconductor. The results demonstrated a link between the phenomena of electron-boson coupling and superconductivity. A boson can be a force-carrying particle, such as a photon, or composite particle of matter, such an atomic nucleus with an even number of protons and neutrons.

“Below the critical temperature of the superconductor, ultrafast excitations triggered a synchronous decrease of electron self-energy and the superconducting energy gap that continued until the gap was quenched,” says Lanzara. “Above the critical temperature of the superconductor, electron–boson coupling was unresponsive to ultrafast excitations. These findings open a new pathway for studying transient self-energy and correlation effects in solids, such as superconductivity.”

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