Studying and refining the properties of “magic” graphene

Recent advances in the development of devices made from 2D materials are paving the way for new technological capabilities, particularly in the field of quantum technology. However, until now, little research has been conducted on energy losses in strongly interacting systems.

With this in mind, the team led by Professor Ernst Meyer from the Department of Physics at the University of Basel used an atomic force microscope in pendulum mode to study a graphene device in more detail. For this, the researchers used two-layer graphene, made by colleagues at LMU Munich, in which the two layers were twisted by 1.08°.

When stacked and twisted relative to each other, the two layers of graphene produce “moiré” superstructures and the material acquires new properties. For example, when the two layers are twisted at the so-called magic angle of 1.08°, graphene becomes a superconductor at very low temperatures, conducting electricity with virtually no energy dissipation.

Refine properties

Using atomic force microscopy (AFM) measurements, Dr Alexina Ollier was now able to prove that the twist angle of graphene atomic layers was uniform across the entire layer, at around 1.06°. She was also able to measure how the current-conducting properties of the graphene layer can be changed and adjusted depending on the load applied to the device.

Depending on whether individual graphene cells were “charged” with electrons, the material behaved like an insulator or semiconductor. The relatively high temperature of 5 Kelvin (-268.15°C) during the measurements means that the researchers did not achieve superconductivity in graphene, because this phenomenon (current conduction without energy dissipation) only occurs ‘at a much lower temperature of 1.7 Kelvin.

“But we were able not only to modify and measure the current conduction properties of the device,” explains Ollier, first author of the study published in Physics of communications“but also to impart magnetic properties to graphene, which, of course, only consists of carbon atoms.”

“It is an achievement that we are able to image tiny flakes of graphene in electrical components, change their electrical and magnetic properties and measure them precisely,” Meyer says of this work, which was part of a doctoral thesis at the SNI Ph. D. School. “In the future, this method will also help us determine the energy loss of various two-dimensional components in the event of strong interactions.”