Prof Yulin Chen

Abstract:

Topological insulators represent a new state of quantum matter recently discovered with insulating bulk but conducting surface states formed by an odd number of Dirac fermions. In this Letter, we report our recent progress on the study of electronic structures of ex-situ grown topological insulator thin films by angle resolved photoemission spectroscopy (ARPES). We successfully obtained the topological band structures of molecular beam epitaxial HgTe and vapor-solid grown Bi2Te3 thin films after proper surface cleaning procedures. This new development will not only enable us to study more topological insulators that cannot be measured by conventional in-situ ARPES technique (e.g. by cleaving or growing samples in-situ), but also open the door to directly characterize the electronic properties of topological insulators used in functional devices. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Abstract:

We report a systematic study of bulk and surface chemical doping effects on single Dirac cone topological insulator Bi2Se3 and Bi2Te3. By bulk doping, we were able to achieve full range control of charge carrier types and concentration, with the exact Fermi energy measured by angle-resolved photoemission spectroscopy (ARPES). Due to the unusual robustness of the topological surface state, we further realized the bi-polar control of the surface carriers by gaseous or alkaline surface doping without affecting the topological nature of these materials. The doping progress monitored by in situ ARPES study clearly demonstrated the switching between different carrier types through the Dirac point. The ability to control the carrier types and the concentration of topological insulators will greatly facilitate future applications. © 2012 IOP Publishing Ltd.