Recent breakthroughs in developing devices made of 2D materials pave the way for new technological capabilities, particularly in quantum technology. However, only a few studies have been conducted into energy losses in strongly interacting systems.
Magic-Angle Graphene
Magic-angle graphene refers to a very particular stacking of graphene where an atom-thin material made from carbon atoms is linked in a hexagonal pattern that resembles chicken wire. When one sheet of graphene is stacked on top of a second sheet at a precise "magic" angle, the twisted structure makes a slightly offset pattern that can support a host of remarkable electronic behaviors.
Pablo Jarillo-Herrero and his MIT team first demonstrated the magic-angle twisted bilayer graphene in 2018. They showed that the new structure can behave as an insulator when they apply a certain continuous electric field. This discovery gave rise to the field of "twistronics," which explores the emergence of certain electronic properties from the twisting and layering of two-dimensional materials.
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Energy Dissipation on Magic Graphene
At the University of Basel, a team of experts performed an experiment where they investigated a graphene device in greater detail. Led by Professor Ernst Meyer from the Department of Physics, the researchers used an atomic force microscope in pendulum mode to fabricate a two-layer graphene.
When the graphene materials are stacked and twisted relative to one another, the two layers create "moiré" superstructures and acquire a new set of properties. For instance, when the magic angle of 1.08 degrees twists the two layers, graphene becomes a superconductor at very low temperatures and can conduct electricity with almost energy dissipation.
In this study entitled "Energy dissipation on magic angle twisted bilayer graphene," the experts proved that the twist angle of the atomic graphene layers was uniform across the entire layer at about 1.06 degrees. The team was also able to measure the changes and adjustments in the current-conducting properties of the graphene layer as a function of the charge applied to the device.
It was found that the material behaved as an insulator or a semiconductor depending on the "charging" of the individual graphene cells with electrons. The high temperature of 5 Kelvin (-268.15 degrees Celsius) during the measurements meant that the scientists did not achieve superconductivity in the graphene. This is because of this phenomenon where current conduction without energy dissipation only occurs at a much lower temperature of 1.7 Kelvin.
The team successfully modified and measured the current-conducting properties of the device. In addition, they were also able to impart magnetic properties to the graphene. From this achievement, the researchers plan to use tiny graphene flakes in electrical components with precise measurements and changes in their electrical and magnetic properties. They believe that in the future, this innovative method can help scientists determine the energy loss of different two-dimensional components in the event of strong interactions.
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