Researchers Develop Sub-Femtosecond Transportation for Electrons

A European team composed of researchers from the University of Konstanz, the University of Luxembourg, CNRS-Université Paris Sud, the Center for Materials Physics, and Donostia International Physics Center in San Sebastián, Spain, has found a way to transport electrons at times below the femtosecond range by manipulating them with light. The researchers believe their findings could have major implications for the future of data processing and computing.

The task for the research team was to develop an experimental setup for manipulating ultrashort light pulses at femtosecond scales below a single oscillation cycle while creating nanostructures suited for high-precision measurements and manipulation of electronic charges. “Fortunately for us, we have first-class facilities at our disposal right here in Konstanz,” said Alfred Leitenstorfer, professor of ultrafast phenomena and photonics at the University of Konstanz and co-author of the study.

Contemporary electronic components, which are traditionally based on silicon semiconductor technology, can be switched on or off within picoseconds (10⁻¹² seconds). Standard mobile phones and computers work at maximum frequencies of several gigahertz while individual transistors can approach one terahertz. A recent series of experiments conducted at the University of Konstanz and reported in Nature Physics demonstrates that electrons can be induced to move at sub-femtosecond speeds, faster than 10⁻¹⁵ seconds, by manipulating them with tailored lightwaves.

“This may well be the distant future of electronics,” Leitenstorfer said. “Our experiments with single-cycle light pulses have taken us well into the attosecond range of electron transport.” Leitenstorfer and his team from the Department of Physics and the Center for Applied Photonics believe that the future of electronics lies in integrated plasmonic and optoelectronic devices that operate in the single-electron regime at optical frequencies. However, Leitenstorfer held off any bold predictions, stating that the research is still “very basic” and may take decades to implement.

Leitenstorfer’s experiment involved nanoscale gold antennas and an ultrafast laser capable of emitting 100 million single-cycle light pulses per second to generate a measurable current. The bow-tie design of the optical antenna allowed for a subwavelength and subcycle spatiotemporal concentration of the electric field of the laser pulse into the gap of a width of 6 nm.

As a result of the highly nonlinear character of electron tunneling out of the metal and acceleration over the gap in the optical field, the researchers were able to switch electronic currents at speeds of approximately 600 attoseconds. “This process only occurs at time scales of less than half an oscillation period of the electric field of the light pulse,” Leitenstorfer said. The project partners in Paris and San Sebastián were able to confirm Leitenstorfer’s observation and create a detailed map of the electronic quantum structure coupled to the light field.

The researchers are hoping the study will open up new opportunities for understanding how light interacts with condensed matter, enabling observation of quantum phenomena on new temporal and spatial scales. Building on the new approach to electron dynamics, the researchers will move on to investigate electron transport at atomic time and length scales in even more sophisticated solid-state devices with picometer dimensions.

For the full study, visit www.nature.com/articles/s41567-019-0745-8.