You can have your conductor and insulator, too

Combining a topological insulator with a superconductor could enable the design of advanced materials with broad potential application in semiconductor electronics and computing, including novel approaches such as spintronics and quantum computing.

Scientists discovered a compound that exhibits the true properties of a topological crystalline insulator, with unusual electronic conduction at the surface but no conduction within the bulk. Theorists have predicted the possibility that certain materials might behave as topological insulators, in which electronic conduction can only take place at the surface by electrons whose spin and momentum are coupled. This coupling has the favorable property of protecting the moving surface electrons from backscattering by imperfections in the material.

Because, ideally, the bulk of the sample is insulating, a current flowing along a sample could only involve spin-polarized surface electrons that are protected by such quantum mechanical coupling. Experimentalists have synthesized a number of compounds that exhibit the predicted topological surface states; however, so far these materials were found to be non-insulating in the bulk, presumably due to atomic-scale defects that are difficult to control. Now, a group of researchers at Brookhaven National Laboratory have discovered a new material (In-doped Pb_1−xSn_xTe) that truly exhibits the predicted properties, with no conduction within the crystal's interior. This discovery could allow for electronic devices that manipulate electronic spin instead of charge and enable tremendous energy savings.