Topological Insulators

In an electrical conductor, negatively charged electrons can hop between atoms and move freely in their interior or on the surface. These free electrons are responsible for the generation of electric current. For most metals, electrons in the interior carry most of the current, while surface electrons are only weakly mobile. Some materials, such as glass, have structures that impede electron flow and are called insulators.

A topological insulator is a substance that acts as an insulator in its interior while permitting the movement of charges on its boundary. This can occur when a perpendicular magnetic field is applied, this is known as the quantum Hall effect.
Princeton scientists have discovered a new type of typological insulator, an antimony crystal, which does not require the application of a magnetic field.

Reference:
Jungpil Seo, Pedram Roushan, Haim Beidenkopf, Y. S. Hor, R. J. Cava, Ali Yazdani. Transmission of topological surface states through surface barriers. Nature, 2010; 466 (7304): 343 DOI: 10.1038/nature09189

Study Questions

1. What is required in order for a material to be considered an electrical conductor.
2. Give three examples of good electrical conductors.
3. Give three examples of electrical insulators.
4. In general, what type of substances conduct electricity?
5. In general, what type of substances do not conduct electricity?
6. If electrons are negatively charged, why are atoms considered to be neutral?
7. Why do you think electrons are more free to move within the interior of a material compared to its surface?