The Strong Side of Weak Topological Insulators

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Traditionally, when it comes to electrical properties, materials are divided into insulators and conductors. Recently, this dichotomy has been found to break down with the prediction of a new quantum state of matter called "topological insulator".

 

A topological insulator is characterized by being insulating in the bulk yet conducting at the surface. Interestingly, the surface conductance results from topological properties of the wavefunctions of the electrons. The discovery of such materials, e.g., Bi2Se3 and Bi2Te3, was all the more intriguing, and initiated a great effort by the physics community to further explore their unusual properties and possible applications. In this talk, we will focus on the so called "weak topological insulator", which lacks some of the properties of the standard topological insulator. It was believed that the conductance at the surface of a weak topological insulator is too fragile to survive in real materials.

 

We argue that the surface conductance of the weak topological insulator is actually robust. Namely, the surfaces conduct even in the presence of strong disorder, which is regularly present due to impurities and defects, as long as the disorder is generic and non-magnetic. Furthermore, we find that the weak topological insulator exhibits unique anisotropy, which suggests the possibility of surface engineering. Recent experimental results supporting these findings will be discussed as well.