Magnetically doped topological insulator thin films

Ke He

 Topological Insulator (TI) is a new class of materials that might show quantum phenomenon under not-extreme conditions. Most of the theoretically predicted exotic properties of TIs result from the interplay between topological surface states and magnetic or superconducting order. Doping magnetic impurities provides an easier way to introduce magnetic order into a TI, a strategy analogous to diluted magnetic semiconductor (DMS). Especially in quantum well films of magnetically doped TIs, long sought quantized anomalous Hall (QAH) effect, namely the quantum Hall effect induced by spontaneous magnetization of material instead of strong external magnetic field, is predicted if both ferromagnetic insulating phase and chemical potential tuning were realized. Combining angle-resolved photoemission spectroscopy, scanning tunneling microscopy/spectroscopy, and transport measurement, we have investigated the electronic structures and properties of epitaxial thin films of magnetically doped Bi2Se3 family three dimensional TIs. Gap-opening in the Dirac surface states and anomalous Hall effect induced by magnetic order have been observed, and their dependences on chemical potential have been systematically studied. In Cr doped BixSb2-xTe3 thin films, anomalous Hall resistance has been found to increase abruptly with decreasing carrier density, while the Curie temperature shows little dependence on the type and density of carrier density. The above results imply that Cr doped BixSb2-xTe3 thin film is a promising system for realization of QAH effect and as well a new and special DMS material that could be applied in spintronics.