MONITORING REPORT ISB: Ultrafast laser techniques have helped MIT physics graduate Fahad Mahmood and fellows establish that electrons form charge-density waves in the thin-film superconductive material LSCO cuprate.

“The question is how does this fluctuating charge-density wave compete or not interfere with superconductivity, and what we found is that it actually competes with superconductivity,” Mahmood explains. “Electrons for a very short amount of time are in this charge-density wave state, and in another time scale, if you take another snapshot, they’ll be in the superconductivity state.”

The charge-density waves occur when electron density in a conductor is distributed in a sinusoidal pattern, like ripples on water, instead of the common uniform density.

“It’s a fluctuating order that lasts for a very short amount of time and equilibrium probes won’t be able to detect it,” he said.

Using ultrafast spectroscopy, Mahmood and co-authors of a 2013 Nature Materials paper were able to show that for extremely short periods of time – up to about 2 picoseconds – electrons clustered in a density wave that could be measured by its amplitude and phase.

Mahmood grew up in Pakistan and won a scholarship to Stanford University, where he studied physics and aeronautical engineering. Now one of Gedik’s students, he expects to finish his PhD program in next June.

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