Scientists Use Light to Transport Electrons at Ultrafast Speeds

A research team led by University of Konstanz scientists has demonstrated that light waves can be used to transport electrons at sub-femtosecond speeds (i.e. faster than 10^-15 seconds).

Electrons move between two arms of a metallic nanoantenna driven by a single-cycle light wave. Image credit: University of Konstanz.

“This may well be the distant future of electronics,” said University of Konstanz’s Professor Alfred Leitenstorfer, co-author of a paper published in the journal Nature Physics.

“Our experiments with single-cycle light pulses have taken us well into the attosecond range of electron transport.”

In the study, Professor Leitenstorfer and colleagues aimed to develop an experimental set-up for manipulating ultrashort light pulses at femtosecond scales below a single oscillation cycle, and to create nanostructures suited for high-precision measurements and manipulation of electronic charges.

“We believe that the future of electronics lies in integrated plasmonic and optoelectronic devices that operate in the single-electron regime at optical — rather than microwave — frequencies,” they said.

“However, this is very basic research we are talking about here and may take decades to implement.”

The team’s experimental set-up included nanoscale gold antennas and an ultrafast laser capable of emitting one hundred million single-cycle light pulses per second.

“The bowtie design of the optical antenna allowed for a sub-wavelength and sub-cycle spatio-temporal concentration of the electric field of the laser pulse into the gap of a width of 6 nm,” the researchers said.

“As a result of the highly nonlinear character of electron tunneling out of the metal and acceleration over the gap in the optical field, we were able to switch electronic currents at speeds of 600 attoseconds.”

“This process only occurs at time scales of less than half an oscillation period of the electric field of the light pulse,” Professor Leitenstorfer said.

“We were able to confirm and map out it in detail by means of a time-dependent treatment of the electronic quantum structure coupled to the light field.”

“The study opens up entirely new opportunities for understanding how light interacts with condensed matter, enabling observation of quantum phenomena at unprecedented temporal and spatial scales,” the scientists said.

“Building on the new approach to electron dynamics driven at the nanoscale by optical fields that this study affords, we will move on to investigate electron transport at atomic time and length scales in even more sophisticated solid-state devices with picometer dimensions.”

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M. Ludwig et al. Sub-femtosecond electron transport in a nanoscale gap. Nat. Phys, published online December 23, 2019; doi: 10.1038/s41567-019-0745-8