Degree Name

Doctor of Philosophy


Institute for Superconducting and Electronic Materials


Two-dimensional topological insulators, characterized by Z2 and Chern invariants, are promising materials for novel device concepts in both topological electronics and topological spintronics. Various analytical and numerical techniques, such as tight-binding models based on symmetry analysis, effective Dirac theory, Slater-Koster microscopic orbital picture and first/second order perturbation theory, are employed to study an interplay between various spin-orbit interaction terms, tunability of topologically trivial and nontrivial bulk band gaps, and switching of edge state con-ductance via helical/chiral edge propagating modes. By employing topological and quantum functionalities of two-dimensional topological insulators with honeycomb lattice structures, various models are proposed for energy-efficient nanoscale topolog-ical field effect transistors such as topological quantum field effect transistor, topo-logical spin field effect transistor, and topological tunnelling field effect transistor. By configuring a two-dimensional topological insulator material with honeycomb lattice structure as a channel between source and drain, it is demonstrated that (i) Rashba spin-orbit interaction can lower the subthreshold swing by more than 25%of the limit imposed by Boltzmann tyranny, and (ii) finite-size effects can reduce the threshold gate electric field required for topological switching between ‘on’ and ‘off’ state in quantum confined nanoribbons with zigzag edges. The obtained results show that there is no fundamental lower bound on threshold voltage and subthresh-old swing in topological field effect transistors, highly contrasting from conventional field effect transistors. Furthermore, it is noted that antiferromagnetic topological insulators with honeycomb lattice structures are promising materials for electri-cal switching of charge, spin, pseudospin, and valley currents via gate-controlled topological phase transition. Topological spin field effect transistor modelled via gate-controlled topological phase transition, which is assisted by finite-size effects, is a completely different concept from previously proposed models based on manipu-lation of edge state spin-polarization via inter-edge tunnelling/interference. Finally, it is shown that backscattering and hence deviation from quantized conductance in topological tunnelling field effect transistors can be evaded by configuring quantum confined nanoribbons of honeycomb Chern ferromagnets with high performance via large inter-edge tunnelling current ratio, ION/IOFF. Since field effect transistor is a basic building block for electronics and spintronics, this study may shed light on the fundamental aspects of topological insulator materials and their use in emergent topological electronics and spintronics technologies.

FoR codes (2008)




Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.