2D Dirac electrons in 3D materials

Quantum materials pack the spooky properties of quantum mechanics into real-life materials you can make, pick up with tweezers and study in the lab. Those of interest to us show special electronic properties of great fundamental interest and have applications potential for future computer and electronics technologies. This thesis studies quantum materials in which the electronic states possess a special kind of twist, giving them a different topology to their regular electronic material cousins. Picturing the difference between a Möbius strip and a regular loop helps us get the idea of objects with differing topology.
The research presented investigates the electronic states directly, using the photoelectric effect in angle resolved photoemission spectroscopy (ARPES) experiments, and was carried out on the candidate quasi-2D Dirac semimetal - SrMnSb₂, a trio of rare earth hexaboride compounds, namely SmB₆, YbB₆ and CeB₆, and on Bi-based 3D topological insulators. All of these materials families are predicted to be of the topological, twisty kind, and the final score from our experimental results from ARPES, combined with a varying mix of transport measurements in high magnetic fields, scanning tunneling microscopy and theoretical calculations of the electronic states is as follows. For SrMnSb₂ the answer is no (= regular loop), for the hexaborides the jury is still out and for the Bi-based topological insulators the answer is definitely yes (= Möbius strip), whereby interesting effects involving extreme ultraviolet illumination offer new methods to understand and tune the twisty electronic states at the surface of these systems.