Topological Insulators a.k.a Quantum Spin Hall E ect

The recent experimental realization of a the quantum spin hall e ect has caused a lot of interest in these topological states of matter. Topological insulators are a new form of condensed matter that are not characterized by a spontaneously broken symmetry. Instead the materials are characterized by topology of the manifold of the occupied bloch states. Topological insulators have the unique property that the surface states are spin polarized based upon the direction the current is owing. Like the quantum hall e ect, the resistance of the surface states is quantized with the quantum unit of resistivity. ∗Electronic address: \[email protected];