What is a Topological Insulator?

July 19, 2012

What is a topological insulator? This is what I have written at the top of my notes from a conversation a couple weeks ago with theoretical condensed matter physics professor Arun Bansil, who has just published two new articles about topological insulators in Nature Magazine. But it took about three pages of frantically scribbled notes before the answer finally began to surface.

I will spare you the wind up of our conversation, which mostly had to do with the fact that I haven’t taken a physics class in over a decade, and get right to it:

A topological insulator is a material whose surface is conductive but whose inside is not. While that may sound pretty straightforward, guess again. There’s no obvious reason why a material of uniform structure should display such different properties in different parts. “It’s all about topology and one of the most basic symmetries of nature—the time reversal symmetry,” said Bansil.

These two key concepts – topology and time reversal symmetry – were totally new to me. In fact, I had no idea there were even multiple kinds of symmetries at all. I’m familiar with mirror symmetry, as you probably are, too. But time reversal symmetry is a bit more mind-blowing. It refers to the basic property of physical laws which guarantees that a ball going up follows the same laws as a ball going down. If you record a video of a ball going up and down continuously, you can’t tell if the movie is in play mode or rewind.

Excerpt from iNSolution Research blog. Read full blog