The curious world of topological materials

In our current’s society ceaseless search for new materials that allow electronic devices to perform better and faster, physics and materials science get a whole lot of credit. Yet the frenzy involves the gadgets’ new features rather than the science behind them. Topological materials are a good example. Have you ever heard about them? As it turns out, they were discovered only in the previous decade, but they may feature inside one of your new devices in the near future. So, let’s explore a bit more these materials and their fascinating properties.

 

What does it mean for a material to be ‘topological’? Well, topology is a branch of mathematics that deals with the properties of geometric objects that do not change once twisted or stretched. The number of holes of a geometric object, for example, is a topological property. Such a number does not change when a given object is twisted or stretched-- meaning that you really need to pierce or break it to change its topological property. With this being said, you could imagine now that two objects can have vastly different shapes while having the same topology or topological properties. Take a donut and a coffee cup with a handle, for example. Despite their completely different shape, they hold the same number of holes, and therefore, the same topological property. In terms of topology, the bottom line is that a donut and a coffee cup are much more alike than a donut and a ball. Isn’t it curious? 

 

For electronic devices, crystalline solids are an extremely important class of materials, and their ability to conduct electricity is especially relevant. Two major types of crystalline solids can be distinguished: those that conduct electricity, called conductors (of which metals are an example), and those that don’t conduct electricity, the so-called insulators. Only in the last decade did physicists and materials scientists figure out that there can be insulators and conductors with special topological properties. They were dubbed ‘topological materials’. It is as if we only knew how to make objects without holes before, like a ball or a disc, and then now we found out how to make objects with holes like donuts and coffee cups! Of course, we are not talking about the number of holes in a block of material here. It is something much more profound.

 

For example, a topological insulator -- like a standard insulator -- will not conduct electricity in its interior. Unlike a standard insulator, however, its surface is always conducting. In this way, topological insulators could for example be used as conductors in electronic circuits by sending the electrical current through their surface! Now you can imagine that the discovery of these materials has created a lot of excitement among scientists and opened up vast new possibilities for the creation of more powerful, smaller and fast electronic devices.

 

As a scientist in this field, I do theoretical studies on the fundamental properties of topological materials, including these questions: How do these materials behave when combined with magnetic or superconducting materials? Or how can we use these materials to build powerful quantum computers? If you ask me more details on how this could be done… Oh well, that would be a story for another entire chapter.

 

The future will surprise us with amazing new applications. Yet, much more investigation and discoveries in this domain are required until you see gadgets out there on the market as result of our research. Non-toxic, easy to grow and functional at room temperature are only few examples of important criteria for industrial production of such materials. And we aren’t there yet… 

 

I am Kristof Moors and I am a post-doctoral researcher in Prof. Thomas Schmidt’s group at the Physics and Materials Science Research Unit in the University of Luxembourg. My work is funded by the Luxembourg National Research Fund.

 

 

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