Doctoral Dissertations


Seng Huat Lee

Keywords and Phrases

Dirac Fermion; Dirac Surface State; Electronic Transportation; Magnetic Topological Insulator; Majorana Fermion; Topological Superconductor


"Magnetic topological insulator (TI) has been theoretically proposed to be a platform for inducing magnetic monopole and exhibit fascinating quantum phenomena, whereas topological superconductor can host Majorana fermions, particles that are their own antiparticles, which can be manipulated for topological quantum computing. In this dissertation, we experimentally demonstrated that by intercalation of different transition metals in the van der Waals gaps of Bi2Se3 TI, magnetism and even superconductivity can be induced. In FexBi2Se3, antiferromagnetism is induced with a transition temperature at ~ 100 K. Coexistence of the Dirac surface state with magnetism in antiferromagnetic TI that has been predicted by the theoretical study is verified. We also found the Dirac fermions originate from the bulk acting as many parallel 2D conduction channels on the material. In MnxBi2Se3, paramagnetism is induced. From Shubnikov-de Haas oscillations and quantum Hall effect (QHE) observation, we found the existence of Dirac fermions originate from the bulk, which is similar to the case of FexBi2Se3. Due to the origin of the QHE in FexBi2Se3 and MnxBi2Se3 systems is from the bulk acting as many 2D conduction channels, the electric-field exfoliation method is invented. This method is capable of obtaining a clean sample from different layered crystalline materials with the thicknesses in the range of nm and expecting to observe QHE from the surface state on both materials. Superconductivity is also induced in NbxBi2Se3 with a critical temperature of Tc = 3.2 K while the Dirac surface dispersion in its normal state is still preserved. The onset of hysteretic magnetization in NbxBi2Se3 below Tc suggests spontaneous time-reversal symmetry breaking in the superconducting state. Superconducting and magnetism mutually assist each other to give rise to a symbiosis state of this two phases"--Abstract, page iv.


Hor, Yew San

Committee Member(s)

Waddill, George Daniel
Medvedeva, Julia E.
Kurter, Cihan
Nath, Manashi



Degree Name

Ph. D. in Physics


National Science Foundation (U.S.)


The National Science Foundation (NSF) under grant numbers DMR-1255607 supported this work.


Missouri University of Science and Technology

Publication Date

Summer 2017

Journal article titles appearing in thesis/dissertation

  • Dirac surface state of the antiferromagnetic topological insulator FexBi2Se3
  • Multilayered quantum Hall effect in paramagnetic ordered topological insulator MnxBi2Se3
  • Time-reversal symmetry breaking superconductivity in topological materials
  • Electric-field exfoliation of layered crystalline materials


xiii, 121 pages

Note about bibliography

Includes bibliographic references.


© 2017 Seng Huat Lee, All rights reserved.

Document Type

Dissertation - Open Access

File Type




Thesis Number

T 11348

Electronic OCLC #