Observing, Creating and Addressing Topological Spin Textures in a Monolayer XY Magnet

In a series of pioneering works in the early 1970's, John Kosterlitz and David Thouless first connected the concept of topology to the physics of solids. The basis of this framework is the discrete topological unit, an object defined by its resistance to being smoothly deformed into a continuous background, in the way a disk cannot be smoothly deformed into a ring or torus. Kosterlitz and Thouless showed that the most favourable configurations of the systems they explored must host these topological units. They then went on to predict a material phase transition without symmetry breaking based on these objects, violating all known theories and observations at the time. This so-called topological phase transition has subsequently been used to describe transitions in thin-film superconductors, liquid crystals, and two-dimensional magnets. For this work, Kosterlitz and Thouless shared the 2016 Nobel Prize. Yet, despite the groundbreaking nature of these findings and their subsequent wide-ranging experimental support, the topological units originally predicted have never been observed at the single unit level.

In this programme of work, we will use highly advanced microscopy techniques to "see" each of these topological objects for the first time. The unparalleled resolution of these microscopes can be further used to map the interior of the objects all the way down to their atomic building blocks. These experiments, when combined with advanced computational approaches to the original problem considered by Kosterlitz and Thouless, will provide an entirely new microscopic portrait of these topologically protected objects.

Yet, this work aims far beyond simply observing the topological units; we will develop and deliver a series of approaches to actively manipulate these objects. The first set of techniques for manipulation will utilize influence from the microscope itself, in much the same way a magnifying glass can be used to start a fire. The second...