Fundamentals of low-dissipation topological matter

Power consumption and power losses are not only a major concern for a sustainable future, they are also the largest challenge facing the continued downscaling of electronics. Traditional electronics and magnetic storage are intrinsically lossy, due to electrical resistance and magnetic hysteresis. On the other hand, solid state physics has recently seen several significant breakthroughs at a fundamental level: the discovery of topological insulators and unconventional superconductors. These new states of matter pave the way towards the lossless manipulation of charge, spin and other quantum entities which can transfer information. This project has focussed on quantum mechanical effects related to electronic structure and transport of charge and spin of electrons, which is the source for most forms of electricity and magnetism. The study of charge- and spin-transport in systems where multiple symmetries are broken has also offered a fertile arena in terms of exploring new fundamental physics which can lead to ultra-low-power (superconducting) electronics. In this project, we have calculated and measured fundamental properties of novel materials where magnetism, spin-orbit coupling, and/or superconductivity interact, and have demonstrated possible routes to control charge and spin-currents by external control parameters. Already in the first stages of the project, several important breakthroughs for emergent quantum protodevices were achieved. The project team and collaborating partners have further developed the understanding of quantum confinement in silicon and have shown that it is possible to simultaneously quantise both the conduction and valence bands, as well investigating the origin of superconductivity in similar quantum confined dopant layers in diamond. The project team has also developed an improved understanding of many-body (electron-phonon) physics in 2D materials, as exemplified by graphene. The project team have participated in many international meetings and collaborations, as well as making this work the focus of multiple M.Sc. thesis. In the latter half of the project, we have focussed on understanding and manipulating superconductivity in 2D materials (especially graphene and its semiconducting analogue hBN). Our research work has very successful: a large number of publications (27) in international journals of the highest level have appeared (including Nature Materials, NPJ Quantum Materials and Physical Review Letters). These publications cover a broad range of relevant topics, from method development, to quantum device physics to the fundamental physics of novel spintronic and superconducting materials. Similarly, our work has been presented at a number of international conferences, specialised international meetings, national and local events. Four master thesis have also appeared based on activities based on aspects of this project, and a Ph.D thesis has been submitted for public defence in Feb 2021.

The primary objective of this project has been to increase an understanding of the underlying physics relevant for ultra-low-power device applications. The primary impact for the research field is that the results generated here will facilitate `the next step' towards realising working devices - specifically, seeding new application-oriented projects to construct and demonstrate novel devices with superior performance than is currently available.

Applications related to the synthesis of electricity and magnetism are currently being actively pursued at the nanometer scale. The topics included in this research proposal mainly revolve around quantum mechanical effects related to electronic structure and transport of charge and spin of electrons, which is the source for most forms of electricity and magnetism. The study of charge- and spin-transport in systems where multiple symmetries are broken also offers an important arena for research in terms of fundamental physics. We shall calculate and measure fundamental properties of low-dissipation hybrid structures comprised of materials where magnetism, spin-orbit coupling, and/or superconductivity are present in topologically non-trivial matter, with the objective to reveal possible ways of controlling charge- and spin-currents in a well-defined manner by external control parameters. This will be done in the context of topological insulators, topological superconductors, and ferromagnetic or antiferromagnetic insulators. The overarching theme in the project proposal is to illuminate the subtle interplay between different types of emergent or broken symmetries when they appear simultaneously in condensed matter systems with the long-term potential for applications in low-power consumption devices.