When the founders of Quantum Mechanics talked about the wave functions of electrons in atoms and solids, I doubt they imagined that those wave functions would ever be imaged in experiments. Scanning tunneling microscopy (STM) has opened up that possibility, and the images obtained are seriously beautiful. (A technical aside is that really it is not the wave function that is imaged, but the density of electronic states, but let's not be picky.) Electron waves break against triangular islands, atomic mountains rise out of the sea of electrons, and cliffs drop sheerly down to the ocean when one type of nano-structure ends and another begins.
In fact, from an aesthetic point of view, the maps of these electronic densities of states rival the astrophysical images I talked about in my last blog entry. Indeed, I think that the pictures from the Colloquium yesterday were as good as any in a talk about galaxies. They definitely added to the presentation, helping to give an intuitive picture of what was going on. My personal favourite was an image that showed what one my colleagues referred to as "the STM spin bombing the surface". As he said, most appropriate, given that Hamburg was hard hit by Allied bombs during WWII.
Joking aside, I thoguht it a very good Colloquium. Starting from STM basics, Prof. Wiesendanger showed why it is even more interesting to do spin-polarized STM. The patterns of anti-ferromagnetic strips imaged in the experiments of his group reveal details of the microscopic interactions that lead to the structures on these surfaces. But even more impressive was the ability to image single atoms on the surface. Indeed, Prof. Wiesendanger's group has a recent paper in Science where they obtain magnetization ("hysteresis") curves for these isolated atoms, and from those curves glean information on the spin-dependent interactions between the atom and a nearby magnetic "cliff".
For me, I found it pretty wonderful to see elementary Quantum Mechanics in action (e.g. solutions for a particle in a triangular box being realized in some of these systems). But at another level understanding the magnetic (i.e. spin-spin interaction) properties in these systems---and using STM tips to manipulate those spins---potentially opens up a variety of new technologies. Like Manasvita said, exploring fundamental science leads to exciting new technologies, and not necessarily in ways that you'd expect.
So, did you have a favorite picture? (You can see some of them again by clicking on the link above that takes you to the Weisendanger group website in Hamburg.) Does seeing images like this make Quantum Mechanics more real for you?
