Physicists Control Electrons at Femtosecond Timescales

When you shine a light on a conducting surface like silicon or graphene, that light jump-starts certain electrons into high-energy states and kicks off a cascade of interactions that happens faster than the blink of an eye. Within just a few femtoseconds — a thousand trillionth of a second — these energized electrons can scatter among other electrons like balls on a billiard table, quickly dissipating energy in an ultrafast process known as thermalization.

Now physicists at MIT have come up with a way to manipulate electrons in graphene within the first few femtoseconds of photo-excitation. With their technique, the researchers can redirect these high-energy electrons before they interact with other electrons in the material.

The team’s ultrafast control of high-energy electrons may ultimately lead to more efficient photovoltaic and energy-harvesting devices, which capture photo-excited electrons before they lose their energy to thermalization.

“We’re intellectually excited about whether this will have technological applications,” says Pablo Jarillo-Herrero, associate professor of physics at MIT. “It’s too soon to know, but there are certain angles of looking at this where it's clear there might be ways to engineer energy flow or transfer in ways that are novel. Now we need more people thinking about this.”

The group’s results are published this week in the journal Nature Physics. Jarillo-Herrero’s co-authors include lead author and graduate student Qiong Ma, along with Jing Kong, professor of electrical engineering and computer science, and Nuh Gedik, associate professor of physics.

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