Quantum Effects in 2D Dirac Materials with Strong Spin-Orbit Coupling: From Spin-Orbit Torques to Quantum Interference Phenomena

In the last decade, spintronics has emerged as a major field in condensed matter physics. It aims to use the spin degree of freedom of charge carriers to store, process and transmit information. Offering low power consumption and high efficiency devices, it represents a path towards the next step up for modern electronics. Spin-orbit torque (SOT) is a spintronics-based phenomenom. It makes use of the coupling between the electronic spin and momentum present in some systems to electrically control the magnetisation of magnetic materials. Two dimensional (2D) materials offer an ideal venue for spintronics applications due to their low dimensionality, versatility and tunability. Vertical stacking of different layers allows for a remarkable control of the resulting properties. This includes the engineering of the much sought after spin-orbit coupling (SOC) via proximity interaction. The effects of strong SOC in these heterostructures, however, remains fairly unexplored. The aim of this thesis is twofold: to understand how SOC changes the quantum interference effects, and to develop a microscopic theory for SOT in disordered 2D Dirac heterostructures. In Dirac materials the interplay between spin, pseudospin and isospin vastly enriches the picture of quantum interference corrections. We find that an unconventional SOC-driven weak localisation phase arises due to spin-pseudospin coupling. Intervalley scattering recovers the standard weak anti-localisation making detecting it very challenging. Interesting results arise in ferromagnetic Dirac heterostructures. We find new skew-scattering-induced spin responses: a collinear Edelstein effect and out-of-plane spin response. Both constitute robust sources of damping-like SOT and are highly sensitive to disorder strength. We show how all the responses can be interpreted in terms Fermi surface spin textures. In gapped systems the SOT becomes highly anisotropic and a non-perturbative approach is necessary. These findings provide new insight into the nature of SOT in ultra-thin structures.