“`html

Transferring excitons with illumination and a nano-ridge may assist in bridging optics and electronics, facilitating innovative devices and swifter, more efficient communication

A novel nanostructure serves as both a wire and switch that can, for the initial time, regulate and steer the flow of quantum quasiparticles termed excitons at ambient temperature.

The transistor-like switch created by engineers from the University of Michigan could enhance data transfer speeds or even facilitate circuits operating on excitons instead of electricity—setting the foundation for a new category of devices.

Due to their lack of electrical charge, excitons possess the capability to transmit quantum information devoid of the losses associated with electrically charged particles such as electrons. These losses contribute to heat generation in devices like smartphones and computers during operation.

“One can observe the boundaries of electronics being reached now as AI and other intensive calculations stress energy consumption and produce excessive heat. If large processing facilities operated using excitonics instead, this enormous energy consumption could be significantly reduced,” remarked Mack Kira, co-lead author of the study in ACS Nano, supervisor of the theoretical research, and a professor of electrical and computer engineering.

Although less recognized than electrons, excitons are already widely utilized in energy conversion—operating in lighting systems, solar panels, and more. The development of this new apparatus received partial federal funding from the U.S. Army Research Office and the U.S. Air Force Office of Scientific Research.

“Our mobile device displays rely on organic LEDs, which are fundamentally based on excitons,” explained Parag Deotare, co-lead author, supervisor of the practical work, and an associate professor of electrical and computer engineering. “Plants even convert light into excitons for photosynthesis, subsequently transporting that quantum energy packet to required sites before transforming it into chemical energy.”

Excitons are generated in semiconductors when an energy source excites an electron, prompting it to leap from the ground state to an excited state—similar to climbing a rung on a ladder. As the electron ascends, it leaves behind a positively charged vacancy, or ‘hole.’ The negatively charged electron and positively charged hole attract each other and move as a unit, thereby forming a net neutrally charged exciton.

While the neutral charge of an exciton permits it to shift without incurring losses, it presents a challenge: directing excitons intentionally is difficult. Negatively charged electrons are straightforward to steer in a current since a positively charged electrode draws them in, but this principle does not apply to neutral particles.

To engineer a device capable of manipulating excitons, the team employed an approach they had previously established, which creates an energy landscape in space that guides excitons along a physical ridge—the exciton’s version of a wire. An element of this recent innovation involves controlling the exciton flow with electrodes placed on either side of the ridge, acting like a gate.

“When the electrodes are activated, the voltage establishes an energy barrier that inhibits the excitons from advancing. When the voltage is deactivated, the excitons resume their flow.

“““html

“A switch of this nature has not been created until now,” stated Zhaohan Jiang, a doctoral student in electrical and computer engineering at U-M and the primary author of the research.

During evaluations, the apparatus exhibited an on-off switching ratio surpassing 19 decibels, an ample distinction to enable sophisticated optoelectronic uses such as high-speed on-chip data transfer links, utilized in cutting-edge supercomputers, data centers, AI-integrated smartphones and wearables, self-driving vehicles, digital twins, and more.

The other element of the novel method is how it utilizes light to propel the excitons toward the appropriate direction, rendering the device an ‘optoexcitonic’ switch. Beyond generating the excitons by enabling electrons to ascend energy levels, the light interacts with the excitons and aids in advancing them along the ridge.

Collectively, the ridge design and light interaction effectively transported excitons in a single direction over 4 micrometers in under half a nanosecond at room temperature. As a subsequent milestone, the team intends to connect numerous excitonic switches.

“While this innovation could evolve into an optoexcitonic circuit as it develops, I foresee it primarily enhancing the connection between photonics and electronics, which will accelerate processing and communication,” remarked Deotare.

This breakthrough could be pivotal in addressing the swiftly growing need for high-speed data transfers in data centers and potentially in AI and machine learning applications.

The team has sought patent protection with the support of U-M Innovation Partnerships.

This apparatus was constructed in the Lurie Nanofabrication Facility and simulations were conducted on U-M Advanced Research Computing resources, both of which are managed and supported through indirect cost allocations from federal grants. The grant numbers for the Army Research Office are W911NF-21-1-0207 and W911NF2110116, while those from the Air Force Office of Scientific Research are FA995-22-1-0530, FA99500-21-1-0410, and NSF-DMREF 2118809.

“`