Graphene’s Quantum Magic: Perfection in Exaggeration

The hexagon lattice is characteristic of graphene, a wave that reflects the flow of electrons. Credit: TU WIen

Carbon material graphene It has excellent electronic properties. But are they stable enough to be useful in practice? The new statistics say: Yes.

A new computer model shows that graphene’s unique electronic properties remain stable, even with defects, confirming its potential in quantum technology and sensing applications.

Reality in Materials Research: The Case of Graphene

Nothing in the world is perfect. This is also true in the research of weapons. In computer simulations, one often represents the system in the most appropriate way; for example, one calculates the properties that a perfect crystal would have. In reality, however, we often face additional effects – with defects in the crystal lattice, with additional particles attached to the material, and with complex interactions between particles. The important question then is: Do these additional unavoidable effects change the properties of the material or not?

This is particularly interesting in the case of two-dimensional graphene, which contains only one layer of carbon atoms. It has long been known that graphene has excellent electronic properties. However, it was not clear until now how stable these properties are. Are they destroyed by distractions and side effects, which are inevitable in practice, or do they remain strong? The Vienna University of Technology (TU Wien) has now succeeded in developing a comprehensive computer model of realistic graphene structures. It turned out that the desired results were very stable. Even imperfect pieces of graphene can be put to good use in technical applications. This is great news for the global graphene community.

Electron Flow in Graphene

“We calculate at the atomic scale how electricity spreads in a small piece of graphene,” says Prof. Florian Libisch from the Institute of Theoretical Physics at TU Wien. “There are different paths an electron can take in matter. According to the laws of quantum physics, it doesn’t have to choose one of these paths; an electron can take many paths at the same time.”

These different approaches can interact in different ways. At special values ​​of energy, the paths cancel each other out; with this power, the probability of electrons passing through a piece of graphene is very low, and the electric current is small. This is called “destructive disorder”.

Florian Libisch explains: “The fact that the current flow decreases significantly at certain energy values ​​for physical reasons is very desirable in technology.” “This can be used, for example, to process information on a small size scale, similar to what electronics do in computer chips.”

One can use it to develop novel quantum sensors: Suppose a piece of graphene is completely discontinuous. Then, suddenly, a molecule from outside sticks to the surface of the graphene. Dr. Robert Stadler says: “This molecule changes the electronic properties of the graphene piece, and that can be enough to quickly increase the current flow to extremes. “This can be used to make very sensitive sensors.”

Complex Objects and Movements in Graphene Modelling

However, the physical effects that play a role in the details are very complex: “The size and shape of a piece of graphene is not always the same, and there are many-body interactions between many electrons that are very difficult to calculate mathematically. There may be extra atoms that are not wanted in some places, and the atoms are always slightly wobbly – all this needs to be taken into account to be able to describe the graphene material in a really reasonable way,” says Dr. Angelo Valli.

This is exactly what has already been achieved at TU Wien: Angelo Valli, Robert Stadler, Thomas Fabian, and Florian Libisch have years of experience in accurately describing various effects on objects in computer models. By combining their skills, they have now succeeded in developing a comprehensive computer model that includes all relevant sources of error and disturbing effects present in graphs.

In doing so, they were able to demonstrate that despite these sources of error, the desired results are still evident. It is possible to find some energy where the current flows only at a very small rate due to quantum effects. Experiments have already shown that this makes sense, but systematic theoretical research is lacking until now.

This proves that graphene does not have to be perfect to be used for quantum information technology or quantum sensing. For applied research in this area, this is an important message: Global efforts to use quantum effects in graphene in a controlled way are really promising.

Reference: “Stability of antiresonances of destructive quantum interference in electron transport through graphene nanostructures” by Angelo Valli, Thomas Fabian, Florian Libisch and Robert Stadler, 10 August 2023, Carbon.
DOI: 10.1016/j.carbon.2023.118358