Wednesday, March 14, 2012

Not reported correctly, but interesting

Before you read the SciTech story about "designer electrons", be aware that the reporter is pretty confused. The electrons in one configuration do not have mass 0 and move at the speed of light. A waveform does. The electrons in another are squeezed around "as if they had been exposed to a real field" which is not terribly startling since the configuration was designed to squeeze them, just as we can build a truss that looks like it has been bent.

What the researchers from Stanford and SLAC did was interesting enough without the hyperbole and mis-statement. On a smooth copper surface they used a scanning electron microscope to position carbon monoxide molecules in a pattern that mimicked the holes in a graphene lattice. Electrons in the copper surface avoid the CO molecules on the surface, and so behave as though they were really in a graphene lattice. But more than that, when the researchers put the CO molecules on in a distorted pattern, the electrons behaved as though the lattice was distorted e.g. by a magnetic field. And all worked out as calculated.

So this might be a test-bed for predicting how materials behave in strong magnetic fields--up to the point where real fields would start causing substantial distortions in real molecules. Then the model would fall down.

The drawback is the rather tedious placement of the molecules. I find it amazing that we can do that at all, much less plant so many, but they do it.


Assistant Village Idiot said...

How do the particles "know?" Or is this like asking how does the thermos "know."

james said...

The electronic configuration of the CO molecule adhering to the surface of the copper makes changes in the local probability density for the electrons. This would only be a surface phenomenon, but for thin films surface phenomena dominate.

I'd have to do some moderately hairy calculations to verify their claim that it sort of "pushes" the copper electrons away, and I'm over 35 years rusty on molecular physics. But surface effects are pretty weird, and it is plausible.