Hand in Hand: Using the handedness of X-rays to probe the handedness of electronic vortices

Chirality – or handedness – is an intriguing symmetry property in nature and it simply means that a chiral system is non-superposable on its mirror image. An example of a chiral system we all know are our hands: When the thumbs point in the same direction, the palms are opposite. Your hands are mirror images, but not superposable. Each hand is therefore chiral. Chirality is present in many forms and at many scales, from the spiral-staircase design of our own DNA to the spin and drift of spiral galaxies – it can even determine whether a molecule acts as a medicine or a poison in our bodies. However, to engineer and control chirality on the nanoscale is very difficult. Prof. Ramesh’s group recently developed a way to make electronic nano vortices in a controlled manner. The systems included alternating thin layers of lead titanate and strontium titanate to form a synthetic material known as a superlattice. Neither of the two compounds show any handedness independently, but when they were combined into the precisely layered superlattice, they developed swirling electronic vortex structures.

To determine if the vortices actually show chirality or handedness Prof. Arenholz’ group used circularly polarized soft X-rays – which exhibit a handedness of their own – and diffracted them from the superlattices. It turned out that the diffraction intensity depends on both the handedness of the X-ray and the handedness of the electronic vortex structures providing a new and exciting probe for nanoscale chirality.

This work is published in the Proceedings of the National Academy of Sciences (PNAS) here.