Chemical doping effects in topological insulators
March 29, 2012 - 10:00am
Topological insulators, a novel kind of three-dimensional insulators can have a bulk insulating gap but non-trivial topological surface states. The surface states of these topological insulators show Dirac-like behavior with the spin polarization locked perpendicular to the electron momentum by the effect of strong spin-orbit interaction. As the locking protects the surface electrons from back scattering, they are predicted to have high mobilities. The surface state of Bi2Se3 and Bi2Te3 topological insulators has been observed by angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM), but is still considered a challenging problem for electronic transport measurements due to the dominant bulk conductance in the materials. We have found that by chemical doping, the chemical potential can be tuned to fall inside the band gap and therefore suppress the bulk conductivity. The Bi2Se3 topological insulator can also be tuned to a bulk superconductor, with Tc ~ 3.8 K, by copper intercalation in the van der Waals gaps between the Bi2Se3 layers. This shows that Cooper pairing is possible in Bi2Se3 with implications for study of Majorana fermion physics and potential quantum computing devices. Furthermore, Mn-doped Bi2Te3 has ferromagnetic transition at about 13 K, suggesting that it may be a magnetic topological insulator.