Researchers at McGill University have developed a novel device that generates sound-like particles known as phonons at extremely cold temperatures. The technology could be used to create phonon lasers, with possible applications in communications and medical diagnostics.
"Modern communication is largely based on light, including electromagnetic waves and electrical currents. In a medium such as oceans, sound can travel, whereas light and electrical currents cannot," said Michael Hilke, Associate Professor of Physics and study co-author. "In the human body, sound waves can also be a useful tool."
The device was built and analyzed at McGill and the National Research Council of Canada. The material was synthesized at Princeton University.
Fast electrons create sound-like vibrations
The device works by sending an electrical current through a two-dimensional layer of crystal, trapping electrons in a channel within an area just a few atoms thick. The researchers found that when electrons are pushed hard enough through this channel, they release energy as bursts of sound‑like vibrations, called phonons, in predictable and tunable patterns.
This is made possible by cooling the devices to temperatures between about 10 milli-Kelvin and 3.9 Kelvin, which makes electrons behave more predictably and allows researchers to observe quantum effects, which occur when matter behaves as waves rather than as solid particles.
"At absolute zero temperatures - that is, the world of quantum physics - no sound is created unless electrons travel collectively at the speed of sound or above," Hilke explained. "Earlier work had observed related effects as electron speeds approached the sound barrier. Our study goes further by pushing the system well beyond that point and showing that existing theories need to be reassessed by considering that electrons can be very hot even if the host crystal is close to absolute zero temperature."
New materials could accelerate device speed
Hilke said the next step is to explore how constructing the device with other materials, such as graphene, would allow it to operate even faster.
This could lead to high-speed communications technology, as well as sensing tools, biological materials and advanced medical systems.
"Phonons are hard to generate and harness in a controlled way, so we are exploring new regimes. At a broad level, this is about how electrical current and energy moves and is converted inside advanced electronic materials," he said.
About this study
"Resonant magnetophonon emission by supersonic electrons in ultrahigh-mobility two-dimensional systems," by Michael Hilke et al, was published in Physical Review Letters.
The study was funded by the Natural Sciences and Engineering Research Council of Canada and the Fonds de recherche du Québec - Nature et technologie.
