Graphene earns its stripes: New nanoscale electronic state discovered on graphene sheets

November 29, 2011
These are electronic stripes, called "charge density waves," on the surface of a graphitic superconductor. Credit: K. A. Rahnejat

Researchers from the London Centre for Nanotechnology (LCN) have discovered electronic stripes, called 'charge density waves', on the surface of the graphene sheets that make up a graphitic superconductor. This is the first time these stripes have been seen on graphene, and the finding is likely to have profound implications for the exploitation of this recently discovered material, which scientists believe will play a key role in the future of nanotechnology. The discovery is reported in Nature Communications, 29th November.

Graphene is a material made up of a single sheet of just one atom thick, and is found in the marks made by a graphite pencil. Graphene has remarkable physical properties and therefore has great technological potential, for example, in transparent electrodes for flat screen TVs, in fast energy-efficient transistors, and in ultra-strong . Scientists are now devoting huge efforts to understand and control the properties of this material.

The LCN team donated extra to a graphene surface by sliding calcium underneath it. One would normally expect these additional electrons to spread out evenly on the graphene surface, just as oil spreads out on water. But by using an instrument known as a , which can image individual atoms, the researchers have found that the extra electrons arrange themselves spontaneously into nanometer-scale stripes. This unexpected behavior demonstrates that the electrons can have a life of their own which is not connected directly to the underlying atoms. The results inspire many new directions for both science and technology. For example, they suggest a new method for manipulating and encoding information, where binary zeros and ones correspond to stripes running from north to south and running from east to west respectively.

This work is part of an ongoing multi-disciplinary research effort into graphene at the LCN and follows on from the original discovery of superconductivity in the graphite superconductor CaC6 by Weller at al. published in Nature Physics, doi:10.1038/nphys0010.

Professor Jan Zaanen of Leiden University and winner of the prestigious Spinoza prize for, among other things, his role as proponent of the stripe concept for atomically thin materials, commented: "This discovery is another important step towards demonstrating the ubiquity of stripes, and the fact that they appear in the world's simplest host – the two-dimensional network of carbon atoms that is graphene – means that more great science and applications are not far behind."

Explore further: Scientists make magnetic new graphene discovery

More information: The paper 'Charge density waves in the graphene sheets of the superconductor CaC6' appears in Nature Communications on 29th November 2001. DOI: 10.1038/ncomms1574

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not rated yet Nov 29, 2011
One would normally expect these additional electrons to spread out evenly on the graphene surface, just as oil spreads out on water.
Why the hell should do it? Such idea completely ignores both intrinsic regular structure of electron orbitals within carbon mesh, both repulsive charge of electrons...

Even free particles inside of gas aren't randomly arranged, when they're subject of repulsive forces in the same way, like the electrons. They're forming so called Wigner's crystal exhibiting charge density waves called the Bloch waves.

This is example of so-called scientific journalism, which is pretending, that the results are more fundamental, then they really are for the sake of further grant support.
not rated yet Nov 29, 2011
This approach just leads to the confusion of laymans, who cannot orient in scientific articles, because everything is presented as a very new finding. They cannot see the ways between the trees, they cannot learn anything new from it. Such approach both parasites of the gullibility of laymans, both it enables the way for further trivialization of basic research, which is serving as a safe job generator for people involved. The mainstream science never misses the way, how to serve as a new omniscient Church for the layman public.
not rated yet Nov 30, 2011
Why the hell should do it?

Because electrons are negatively charged and repel each other. It would only be natural to assume that they spread out.

Wigner crystals only occur under very extreme conditions (high temperatures/high pressures.)
Bloch waves require a periodic medium. Graphene is a homogeneous material.

Although it has a hexagonal structure it's surprising that there would be no other electron dispersion (in a tetraeder or larger hexagonal mesh symmetry if the underlying structure was the dominant factor)

This possibly points at something else: intrinsic synchronization of electron spin and/or phase along the axes of symmetry in graphene. This can then create the periodic potential wells into which the extra electrons are funneled.
not rated yet Nov 30, 2011

So these are standing waves, or no ? When you say " intrinsic synchronization of electron spin ", this is similar to aligned magnetic domains ?
not rated yet Nov 30, 2011
this is similar to aligned magnetic domains ?


Could be that the electron positions (or better: the position probability functions of the orbitals) are aligned ... or just the individual magnetic moments (spin) of the outer electrons may be aligned.

But bear in mind that this is just my ad-hoc, knee-jerk hypothesis.

Just saying that this finding is definitely very interesting. With a hexagonal lattice there should be three stable configurations.

The intriguing thing is: Such a material could be used for storage of three-value logic. Maybe even for three-value logic operations.

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