Topological Insulators used to determine fundamental constants

Topological phenomena (TP) play crucial role in determining the precise values of fundamental constants such as elementary charge, Planck constant and speed of light. This is so because of the robustness of topological phenomena against local variation in samples and also weak disorder and interactions between particles. Some famous TP have already been in use to this end: the quanta of magnetic flux has been measured with circular superconducting devices; the electrical conductance has been measured with the help of quantum Hall effect. Recently, a new TP was discovered in materials now known as topological insulators (TI). These materials are characterized by their bulky band gap and gapless surface states that are topologically robust. Examples include Te-Bi type compounds. It is expected that, such TP may also be employed to improve the precision of measurement. This came to realization in a latest publication [PRL 105, 166803 (2010)]:

Fundamental topological phenomena in condensed matter physics are associated with a quantized electromagnetic response in units of fundamental constants. Recently, it has been predicted theoretically that the time-reversal invariant topological insulator in three dimensions exhibits a topological magnetoelectric effect quantized in units of the fine structure constant ¼ e2=@c. In this Letter, we propose an optical experiment to directly measure this topological quantization phenomenon, independent of material details. Our proposal also provides a way to measure the half-quantized Hall conductances on the two surfaces of the topological insulator independently of each other.