Controlling the bulk bandgap and phase transition in topological insulators by combining them with trivial insulators.

Recently, the established division between insulators and conductors was torn down by the remarkable discovery of topological insulators. These materials are bulk insulating, but conducting at their surfaces. They receive a lot of attention for their exotic physics, interesting applications in spintronics and quantum computing and the creation of Majorana fermions (fermions that are their own antiparticles) in these materials.For the few known ones, we need better control over the band structure: most topological "insulators" are actually slightly bulk conducting. A way to tune this is through mixed crystals of topological and trivial (normal) insulators. These also allow to study the phase transition from topological to trivial insulator, for which the mechanism is controversial. So far, such mixed crystals were studied with techniques giving information on the average structure, but not the local structure. However, our preliminary data shows that local order between the different ions exists in several of these. Order will affect the electronic properties.We will study the local order in specific mixed crystals of topological – trivial insulators. We will use state-of-the-art transmission electron microscopy techniques which allow to pinpoint the positions and nature of the different ions at atomic scale. The solved structures will be used to calculate the electronic band structures using Density functional theory calculations. This gives us fundamental knowledge on the mechanism of the topological phase transition as well as the possibility to tune the electronic properties.

Keywords:TOPOLOGICAL INSULATORS, ATOMIC SCALE ORDER, TOPOLOGICAL PHASE TRANSITION, BAND GAPS

Disciplines:Condensed matter physics and nanophysics