Helical DNA filters spins

Spin filters might be salient devices in spintronics. One example of such filters is a ferromagnetic layer, which allows a spin in one direction to pass while blocks it in the other. The selectivity has been shown up to about 25%. Now a study using DNA makes a big difference, where the selectivity can be achieved of as high as 60%. In this case, periodic helice plays an essential role, but how this is so has not been understood yet [Science 18 February 2011: 894-897]. In general, it raises an interesting question on how an electron interacts with chiral supramolecules.

Göhler et al. (3) describe a surprisingly efficient method for electronic spin filtering. They have studied how electrons emitted by a gold substrate, upon absorption of light, pass through a self-assembled DNA monolayer on the gold surface. In particular, they have studied the spin of the electrons after their passage through the DNA layer and have found that one spin type passes through much more easily, meaning that this layer acts as a spin filter, strongly hindering the passage of the other spin type. This filter effect is observed only if the DNA is assembled on the gold surface as a closely packed ordered array of helices, and is stronger if the helices are longer, reaching selectivities of 60%. For chaotic assemblies of floppy DNA chains on the gold surface, the spin filter effect was not observed. [http://www.sciencemag.org/content/331/6019/864.full]