Take a glass thread a thousand times thinner than a human hair. Use it as a wire between two metals. Hit it with a laser pulse that lasts a millionth of a billionth of a second.
Remarkable things happen.
The glass-like material is transformed ever so briefly into something akin to a metal. And the laser generates a burst of electrical current across this tiny electrical circuit. It does so far faster than any traditional way of producing electricity and in the absence of an applied voltage. Further, the direction and magnitude of the current can be controlled simply by varying the shape of the laser — by changing its phase.
Now a University of Rochester researcher — who predicted laser pulses could generate ultrafast currents along nanoscale junctions like this in theory — believes he can explain exactly how and why scientists succeeded in creating these currents in actual experiments.
“This marks a new frontier in the control of electrons using lasers,” says Ignacio Franco, assistant professor of chemistry and physics. He has collaborated with Liping Chen, a postdoctoral associate in his group, and with Yu Zhang and GuanHua Chen at the University of Hong Kong on a computational model to recreate and clarify what happened in the experiment. This work funded by Franco’s NSF CAREER award is now published in Nature Communications.
“You will not build a car out of this, but you will be able to generate currents faster than ever before,” Franco says. “You will be able to develop electronic circuits a few billionths of a meter long [nanoscale] that operate in a millionth of a billionth of a second [femtosecond] time scale. But, more importantly, this is a wonderful example of how differently matter can behave when driven far from equilibrium. The lasers shake the nanojunction so hard that it completely changes its properties. This implies that we can use light to tune the behavior of matter.”
This is exactly what the US Department of Energy had in mind when it listed the control of matter at the level of electrons — and understanding matter “very far away” from equilibrium — among its key challenges for the nation’s scientists.
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