# Top Tech 2013 Day 5: Topological Insulators

Today’s topic is one that we pay some attention to at Prokalkeo, despite the fact that only a couple of our experts know precisely how it works. Topological insulators (or topological semiconductors) are, at the most ‘high level’ description, semiconductors that conduct on the outside, but insulate on the inside. Asking how they do that is more complicated-wikipedia has to say this about them:

A

topological insulatoris a material with time reversal symmetry and trivial topological order, that behaves as an insulator in its interior but whose surface contains conducting states,^{[1]}meaning that electrons can only move along the surface of the material. Although ordinary band insulators can also support conductive surface states, the surface states of topological insulators are special since they are symmetry protected^{[2]}^{[3]}^{[4]}by particle number conservation and time reversal symmetry. (Wikipedia)

Well.

Regardless, they’ve seen a huge amount of development in 2012 and 2013, as concepts that were only speculated on for years finally came to fruition as new materials and metamaterials blossomed. Originally predicted in 2005 and 2006 via topology and material science theory, the first examples showed up in 2008. Topological insulators/semiconductors could theoretically allow for much faster computers by creating arbitrarily shaped robust 2-D devices that can easily manipulate the spin of an electron-the first step on the path to ‘spintronics’. Topological insulators have a number of properties that are exceptionally desirable: electrons pass through them rapidly, their ‘doping’ (which controls the number of charge carriers) can easily be reversed, and they are exceptionally robust due to their topological properties. All of these together, they could prove to be revolutionary in electronics and possibly even quantum computing.

Just two months ago, researchers in the US and China have successfully grown topological insulators on industry standard substrates using an ultra-high vacuum chamber. While they still need to improve manufacturing processes, and the theory behind how exactly topological insulators grow is still confused, researchers can now start to try to build ‘fundamental’ level devices with them (such as simple logic gates and transistors). Last month, a topological insulator was discovered that carried electrical currently differently on top than on the bottom, allowing for even more possibilities.

If you’d like to know more, with links to original research and mind bending math, look at the resources linked below:

IEEE Spectrum Article: http://spectrum.ieee.org/semiconductors/materials/topological-insulators

PhysOrg: http://phys.org/news/2013-10-topological-insulator-materials-future-semiconductor.html