Photoemission Studies of Topological Insulators

Ph.D. Dissertation Turgut Yilmaz Graduate Student UConn Department of Physics Photoemission Studies of Topological Insulators Topological insulators (TIs) attracted scientist due to its distinct electronic structure. TIs possess metallic surfaces due to strong spin orbit coupling, while the bulk shows the insulating behavior. On the surface of TIs topologically protected surface states by time reversal symmetry (TRS) obeys the massless Dirac equation. One of the interest on TIs is to introduce magnetic impurities into bulk and on the surface to break TRS leading to open an energy gap at the Dirac point of TIs. Therefore, x-ray photoemission spectroscopy (XPS) and angle resolved photoemission spectroscopy (ARPES) study on Cr bulk and surface doped Bi2Se3 were presented in order to investigate magnetic impurity doping impact on the electronic and chemical environment of Bi2Se3. ARPES measurements revealed that Cr bulk doping opens an energy gap at the Dirac point without ferromagnetism, while gapless surface states are robust against Cr surface deposition. Another interest on TIs is to obtain proximity induced superconductivity in order to open experimental avenue for possible experimental detection of Majorana fermions. Therefore, we presented ARPES study on Bi2Se3/ Bi2Sr2CaCu2O8+δ (BSCCO) heterostructure in order to search for proximity induced superconductivity. In contrast to expectations, ARPES measurements do not show any sign of the proximity induced superconductivity in the thickness range from 0.5 quintuple layer of Bi2Se3 to 15 quintuple layer of Bi2Se3