Andre Geim
University of Manchester, UK
Imploding atoms have softened this experimentalist's teasing views on theoretical physics.
As an experimentalist, I instinctively dislike theory papers. Too many of them seem to be written for the sole purpose of showing off an integral larger than a competitor's, or to present multiple theories just in case one idea proves right and so is hailed as visionary. I feel even less warmly towards theories that are nigh on impossible to check, such as the supposed precursor to a theory of everything, string theory.
But speaking seriously, even the most obscure predictions can turn out to be spectacularly relevant.
In our lab we have been studying graphene, a material that comprises a single layer of carbon atoms arranged similarly to chicken wire. Because electrons in this material mimic ultra-relativistic particles, it should be possible to observe in their behaviour century-long-predicted phenomena such as the Klein paradox (which concerns how highly energetic electrons tunnel through supposedly impenetrable barriers) and zitterbewegung (jittery movements of relativistic wave-packets).
Several recent theory papers on the physics preprint server arXiv predict another coup for graphene (see A. V. Shytov et al. arXiv:0708.0837; 2007).
According to relativistic quantum theory, atoms containing more than 170 protons cannot exist, because electrons around nuclei with such a large charge would fall into the centre. Nuclear physicists have not come close to creating atoms heavy enough to test this prediction. But the recent theory papers suggest that it should be relatively easy to observe the effect in graphene. This is because electrons in this material interact much more strongly than they do in atoms, so should fall down on charged impurities (standing in for nuclei) rather routinely.
This makes me wonder: could we design condensed-matter systems to test the supposedly non-testable predictions of string theory too?
Comments
Graphene is probably today one of the hotest topics in condensed matter research. The issue of Coulomb impurities can have deep implications for the understanding of the anomalous transport properties of this amazing material, an issue that has impact in the use of graphene for technological applications such as carbon-based electronics.
Hence, it is not surprising that many different groups have been working independently on the same topic, with similar results albeit with different approaches.
I would like to point out our recent publication on the problem:
Vitor M. Pereira, Johan Nilsson, and A. H. Castro Neto, "The Coulomb impurity problem in graphene", Phys. Rev. Lett. 99, 166802 (2007),
where the problem of "fall into a center" is also discussed.
The connections between the low energy physics of graphene and certain theories in high energy particle physics are quite amazing but one word of caution: graphene is a real material made out of atoms on a lattice, hence, analogies with theories in high energy physics have its limitations.
Posted by: Antonio H. Castro Neto | October 18, 2007 04:14 PM
To answer all the complaining e-mails I received in just one day and, in vain hope, to stop the future ones, I have to admit that my sense of humour proved to be too subtle even for decent theorists ;-). Or they might have missed the introductory statement of the blurb that refers to “teasing views”.
I very much appreciate numerous comments that wholeheartedly but so unanimously patronisingly explain to me that there are limitations on analogies between graphene and particle physics, cosmology, the mentioned string theory, etc. Actually, in the original version of the JC note, I wrote about using graphene to prove “creation or string theory”, which was alas overruled by the editors. At least, the creationists do not complain.
Also, my note mentions “several recent theory papers”: There were six references (all in the correct order from the arXiv) but, for the 200 word limit, I was asked to leave only one reference that in my opinion would characterize the topic.
Finally, let me apologize in advance for not answering any future e-mails on the subject.
Posted by: andre Geim | October 19, 2007 11:51 AM