History is repeating itself for Birmingham’s theoretical physicists

An insight into the current research on topological phases of matter, as it was once done in the 1970s

By Chris Oliver As any regular visitor to the University train station will know, the Nobel Prize in Physics 2016 was jointly won by David J. Thouless, John M. Kosterlitz and F. Duncan Haldane.

Kosterlitz and Thouless worked in the Theoretical Physics Group in the School of Physics and Astronomy here at Birmingham during the 1970s, when they completed the work that would make them Nobel laureates. Now history is repeating itself, with that same research group starting work in this field again. But what is this award-winning subject all about, and why does it matter?

The 2016 Nobel Prize was awarded for research into so-called topological phases of matter. These are exotic states of matter that can exist at very low temperatures, where the electrons in the system show very unusual behaviour, compared to familiar solids, liquids and gases. Graphene, another Nobel-winning subject with lots of important applications, is an example of a material that can display these strange properties.

Nowadays, topological phases are back at Birmingham in a new form: topological photonics. Here, scientists are looking for the same unusual behaviour but for systems made of light instead of electrons. 

Why are scientists so excited by this new research? The reason is that light and electrons generally have very different properties, so making them behave in the same way and describing them both using the same theoretical ideas is no mean feat. Scientists have therefore learnt a lot from applying these old ideas about electrons to a different area. Learning new things about the natural world is, after all, the fundamental role of scientists.

This research has more practical benefits for scientists too. Electrons in graphene move over distances in the nanometer range, but the light-based systems built by the scientists are microns in size – this means they are 1000 times larger and therefore 1000 times easier to work with. Now, the experimental observation of topological behaviour in electrons is becoming much more straightforward as it is being modelled after the topological behaviour of light.

One of the most fascinating properties of topological phases could save scientists all this work. It turns out that light moving in these exotic states of matter can just ‘dodge’ impurities and defects and keep moving to produce a nice, clear image.

But perhaps the most exciting aspect of this research is the amazing applications that might come about from this discovery. At the moment, optical devices have huge amounts of money and time being spent on them to make sure they are manufactured in a sterile environment. This means making them in carefully controlled clean rooms to make sure that no impurities get trapped inside the glass and distort the image.

So, after four decades, theoretical physics research at Birmingham has come full circle, from the fundamentals of topological phases to applications in new areas. The future looks bright for this fascinating area of research.