A Breakthrough in Nanotechnology: A Material-Keyboard Made of Graphene

Researchers at ETH Zurich have turned specially prepared graphene flakes into insulators or superconductors by using an electric voltage. This technique functions locally, meaning that the same graphene flake regions with totally different physical properties can be realized side by side.

The production of modern-day digital parts requires materials with diverse properties. There are isolators, for example, which do not conduct electrical current and superconductors that transport it with no losses. To get a specific capability of a component, one generally has to join several such materials together. Typically that is hard, particularly when handling nanostructures that remain in prevalent use today.

A team of researchers at ETH Zurich led by Klaus Ensslin and Thomas Ihn at the Laboratory for Solid State Physics have now been successful in making a material act alternately as an insulator or as a superconductor– or perhaps as both at different areas in the same material– by just applying an electrical voltage. Their findings have been released in the scientific journal Nature Nanotechnology. The work was sustained by the National Centre of Competence in Research QSIT (Quantum Science and Technology).

Magic Angle Graphene

The material Ensslin and his co-workers use bears the rather difficult name “Magic Angle Twisted Bilayer Graphene.” In fact, this name hides something well-understood and straightforward, namely carbon– albeit in a particular form and with a unique twist. The material starts off as graphene flakes, which are carbon layers that are just one atom thick.

The scientists put 2 of those layers on top of each other as though their crystal axes are not parallel but instead make a “magic angle” of exactly 1.06 degrees. Peter Rickhaus, who was involved in the experiments as a postdoc, describes that it is rather tricky, and additionally, the temperature level of the flakes needs to be managed during manufacturing. Therefore, it usually goes wrong.

In twenty percent of the attempts, nevertheless, it works, and the atomic crystal latticeworks of the graphene flakes after that develop a so-called moiré pattern in which the electrons of the material act in a different way than in standard graphene.

Moiré patterns are known from television, as an example, where the interplay between a patterned garment and the scanning lines of the television picture can cause interesting optical effects. In addition to the magic angle graphene flakes, the researchers connect numerous extra electrodes which they can utilize to apply an electric voltage to the material. Something amazing happens when they cool every little thing to a couple of hundredths of a degree above absolute zero.

Depending on the voltage that is applied, the graphene flakes behave in 2 opposite ways: either as a superconductor or as an insulator. This switchable superconductivity was already presented in 2018 at the Massachusetts Institute of Technology (MIT) in the U.S.A. Also, today just a couple of teams worldwide can create such examples.

Insulator and superconductor in the very same material.

Ensslin and his co-workers are now going one step further. By applying various voltages to the specific electrodes, they transform the magic angle graphene into an insulator in one area. Yet, a couple of hundred nanometers away, it becomes a superconductor.

Fokko de Vries, a postdoc in Ensslins laboratory, said that When the team saw that, they initially attempted to realize a Josephson’s joint. In such junctions, two superconductors are separated by a wafer-thin shielding layer. By doing this, the current can not stream directly in between both superconductors; however, instead, it needs to tunnel quantum mechanically through the insulator. That, subsequently, causes the conductivity of the contact to vary as a function of the current in a particular style, depending on whether direct or alternating current is used.

Quantum technologies Applications

The ETH researchers managed to produce a Josephson junction inside the graphene flakes twisted by the magic angle by utilizing different voltages put on the three electrodes, and likewise, to measure its properties. De Vries claims that now that that has worked too, the team can try their hands at more complex gadgets such as SQUIDs. In SQUIDs (“superconducting quantum interference device”), two Josephson joints are attached to develop a ring. Practical applications of such gadgets consist of measurements of small magnetic fields and modern technologies such as quantum computer systems.

For feasible usages in quantum computer systems, an intriguing element is that with the help of the electrodes, the graphene flakes can be transformed not just into insulators and superconductors but additionally into magnets or, in other terms, topological insulators, in which current can only move in one instruction along the side of the material. This could be manipulated to recognize different little quantum bits (qubits) in a single gadget.

A keyboard for products

Ensslin claims that, however, up until now, that is just speculation. Still, he is already enthusiastic regarding the opportunities that occur from the electrical control. Ensslin adds that with the electrodes, the team can practically play the piano on the graphene. Among various other things, the physicists hope that this will undoubtedly help them to obtain brand-new understandings into the complete systems that cause superconductivity in magic-angle graphene.

Originally published by scitechdaily.com

Reference: “Gate-defined Josephson junctions in magic-angle twisted bilayer graphene” by Folkert K. de Vries, Elías Portolés, Giulia Zheng, Takashi Taniguchi, Kenji Watanabe, Thomas Ihn, Klaus Ensslin and Peter Rickhaus, 3 May 2021, Nature Nanotechnology.
DOI: 10.1038/s41565-021-00896-2