The black core of common pencils shows itself to be a promising candidate for the construction of new types of computers based on electron spin

It is not often that a product like the pencil keeps its name, although it has been known for centuries that there is no lead in its core: as early as in the 17th century, a "red tide" had already caused a flood of lead in the pencil. In the nineteenth century, graphite pencils were covered with wood to make pencils. Graphite is one of the three manifestations of carbon.

That one can write so well with it is due to its atomic structure: the carbon atoms are mainly flat tightly bound. The layers built up in this way, on the other hand, are held together only by the weaker van der waals forces, which, for example, also bind the molecules of many oils and fats to one another. If chemical tricks can be used to separate the two-dimensional planes of graphite from one another, so-called graphenes are obtained – very solid, two-dimensional crystals in the x- and y-directions that consist of a single atomic layer.

to compute pencils

This is how a spintronic circuit made of zgnrs could look like

And now where does the computer come into play? The graphene layers, which show (doi: 10.1038/nature05180) three researchers from the university of california at berkeley in the current ie of the scientific journal nature, have the potential to take over the function in new types of computers that semiconductors have in electronics. Although electrons still play the main role, the discipline of spintronics, which is no longer brand new, heightens. It relies on the fact that electrons are characterized not only by their charge, but also by their spin – a kind of angular momentum (although this comparison is not physically correct, but only an analogue). In contrast to the charge of an electron, the spin can even have two states: it can be directed upwards or downwards.

The idea to replace the relatively slow charge-carrier-hole system of electronics by an alternative, where only electrons act as information carriers, has already a few years on its hump. However, it turned out to be relatively difficult to first apply the desired spin to the electrons – and then to protect the information carriers from uninhibited mixing. So a function, which in the electronics the semiconductors take over, which are either p- or n-conductive.

Under certain circumstances, graphene could ame precisely this function, namely to distinguish between up- and down-spin-polarized electrons in terms of conductivity. In their nature paper, the californian scientists investigate exactly which circumstances are responsible for this. The physicists call substances that conduct electrons differently depending on their spin semi-metals – not to be confused with the semi-metals of the chemists in the periodic table of elements.

The prerequisite for graphene to take on semi-metallic properties lies in its frayed edges: special electron potentials can form there. The scientists around steven louie call their objects of investigation zigzag graphene nanoribbons (zgnr). If an electric field is created that propagates in the same plane, the regions in question exhibit semi-metallic behavior. At least, that’s what the computer simulations that louie and co. Have calculated. The spin-related conduction properties of the zgnrs can be controlled via the electric field – who does not think of a transistor?? The graphene ribbons in question are a few nanometers wide and therefore fit well in terms of coarseness into the regions into which microelectronics is currently advancing.

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