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.
Nadeem, Muhammad, Two-Dimensional Topological Insulators for Dissipationless Topological Electronics and Spintronics Technologies, Doctor of Philosophy thesis, Institute for Superconducting and Electronic Materials, University of Wollongong, 2021. https://ro.uow.edu.au/theses1/1143
FoR codes (2008)
0204 CONDENSED MATTER PHYSICS, 0206 QUANTUM PHYSICS, 0299 OTHER PHYSICAL SCIENCES, 0105 MATHEMATICAL PHYSICS
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.