Magnetotransport Methods to Probe Surface States of Topological Insulator Thin Films and Topological Insulator/Ferromagnet (TI/FM) Heterostructures

First part of this thesis is focused on the structural and magnetotransport characterization of Bi2Se3 thin films grown by hybrid physical chemical vapor deposition (HPCVD) method. Bi2Se3 thin films were grown by HPCVD on (0001) Al2O3 substrates with high Se vapor pressure to reduce the occurrence of Se vacancies as the main type of defect. Consequently, the carrier concentration was reduced to ∼5.75x1018 cm-3 comparable to reported carrier concentration in Bi2Se3 thin films.;Magnetotransport measurements were performed on the films and the data was analyzed for weak anti-localization (WAL) using the Hikami-Larkin-Nagaoka (HLN) model. The estimated alpha and l&phis; values showed good agreement with the symplectic case of 2-D transport of topological surface states (TSS) in the quantum diffusion regime. The temperature and angular dependence of magnetoresistance indicated a large contribution of the 2-D surface carriers to overall transport properties of Bi2Se 3 thin film.;The proximity effect at interface of Bi2Se3 TI thin films and superconducting indium contacts is discussed in the second part of this thesis. Low field magnetotransport measurements were performed on Bi2Se3 TI thin films in quantum diffusion regime using superconducting indium dot contacts. We have exploited the coupling of superconducting Cooper pairs with the spin polarized surface states to probe the TSS of Bi2Se3 TI thin films.;Switching in the anisotropic magnetoresistance (AMR) and hysteretic behavior in the magnetoresistance (MR) were observed up to 3.25 K when indium contacts with Tc ∼ 3.40 K were in the superconducting state and vanished at higher temperatures. The magnitude of AMR switching showed a forced current dependence due to current induced spin polarization in Bi2Se3 TI thin films.;The cos2(theta) dependence of AMR of the Bi2Se 3 TI thin films was observed up to 3.25 K and ∼160 Oe when indium contacts were in the superconducting state. 2-D surface transport of the TSS was confirmed by the cos(theta) dependence of field titled MR measurements on the Bi2Se3 thin films. No switching in the AMR or hysteresis behavior in the MR was observed in control experiments performed on non TI materials with superconducting electrodes and metal electrodes on Bi2Se3 TI films.;The growth and characterization of Bi2Se3/Bi 2Se3/La0.70Sr0.30MnO3 (TI/FM), a topological insulator/ferromagnet heterostructure is discussed in the last part of the thesis. We have grown Bi2Se3/Bi2Se 3/La0.70Sr0.30MnO3 (TI/FM) heterostructures by the method of pulsed laser deposition. Bi2Se3/La 0.70Sr0.30MnO3 (LSMO) is a strong ferromagnetic material with Tc ∼ 350 K and Bi2Se3 is the most studied topological insulator.;XRD and phi scan measurements of Bi2Se3/La 0.70Sr0.30MnO3 (TI/FM) heterostructure showed that epitaxial thin films of Bi2Se3 were grown on the LSMO template. Strong in-plane magnetization was confirmed by magnetometry measurements of the Bi2Se3/LSMO heterostructure. Magnetotransport measurements showed a distorted weak anti-localization effect with hysteretic behavior due to interface induced ferromagnetism in the Bi2Se 3 TI films.