Imaging surface magnetism in ruthenates

Abstract

The rapid development of technologies used in computers and consumer electronics is founded in modern condensed matter physics. Advances in the physics of lasers, semiconductors and nanofabrication have enabled precise control of charge transport down to the nanoscale. As the use of electronics grows, energy consumption is becoming an increasingly important issue. One possible path to energy‑efficient technologies is to utilise spin transport in magnetic materials. However, the desirable level of control over magnetic transport is yet to be achieved. Materials with significant electron‑electron interactions, usually called strongly correlated systems, are promising platforms for future technologies. These materials host a range of fascinating phenomena, such as superconductivity, electronic nematicity and various magnetic orders. The ruthenates are a family of materials where many different magnetic ground states are realised. To understand how these magnetic phases emerge and how they can be manipulated, microscopic knowledge of their electronic structure is indispensable. In this thesis, I present a study of magnetism on surfaces of several compounds in the Ruddlesden Popper series of ruthenates, combining low‑temperature scanning tunnelling microscopy in a vector magnet field with theoretical modelling. I show how tiny structural changes at the surface can lead to dramatic changes in magnetic and electronic properties, such as suppression of superconductivity, metal‑to‑insulator transition and stabilisation of magnetic order. In cases where the surface is magnetic, the interplay between magnetism and spin‑orbit coupling makes the electronic properties very sensitive to an external field. This work explored the response of ruthenates to a magnetic field, providing insight into the interplay between their electronic and magnetic structures. Building on this knowledge, other control parameters, such as mechanical strain, electric current or light pulses, could be employed to engineer novel magnetic and electronic states. The materials presented in this work are thus prime candidates for developing future spin‑based electronics.