Abstract
Topological insulators (the first-discovered and best known being Bi2Se3) have insulating bulk but conducting surfaces, and therefore exhibit uniquely exciting electronic properties. Their special surface states are protected by time-reversal symmetry and are hence robust against perturbations. Topological isulators have therefore attracted immense interest in condensed matter physics over the years, especially due to their versatile possible applications in quantum technology. However, due to strong spin-orbit coupling in these materials, applying any magnetization to them leads to novel (otherwise unattainable) quantum states, such as quantum anomalous Hall states, axion insulator states, and high Chern insulators, each of which are of high fundamental importance. Adding magnetization to topological insulators is typically achieved by doping with magnetic (ad)atoms, or constructing heterostructures with magnetic adlayers. In these so-called magnetic topological insulators, the time-reversal symmetry at surfaces may be broken by added magnetization, so unique topological states can appear, characterized by conductance quantized proportionally to the so-called Chern number. In recent years, the study of states with a Chern number higher than one has been at the forefront of research due to their potential application in multi-channel quantum computing and energy-efficient electronic devices (as their resistivity and associated Joule heating reduce proportionally to the Chern number).
This PhD project provides a detailed theory of these emergent novel quantum states in magnetic topological insulators and their computational characterization in terms of stability and phase transitions as a function of size and direction of magnetization, applied magnetic field, sample thickness, strain, or gating. This research is based on initially built advanced (stationary and transport) real-space simulations of magnetic topological systems under external mechanical, electric and magnetic stimuli, using the tight-binding model, Landauer-Buttiker formalism, and material-specific ab initio data calculated in the host research group.
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