First-principles studies of topological matter

Speaker: Irene Aguilera – Institute for Theoretical Physics, University of Amsterdam

Host: Zeila Zanolli

Abstract:

How does one calculate properties of solids in practice? What are the most widely used approximations and what is the physics behind them? In this seminar, I will give an introduction to three of the most popular methods: density functional theory (DFT), the many body quasiparticle GW method, and its self-consistent extension QSGW. I will focus on the physical aspects of these methods rather than on the mathematical formulations, so the seminar is also suitable for non-experts. Comparison to photoemission spectroscopy measurements will show that the GW electronic structures agree much better with experiments than the DFT ones.

I will show applications of these methods to topological materials and will show that standard DFT is unable to provide correctly the critical points of topological phase transitions. This is because the well-known underestimation of band gaps in DFT translates into an overestimation of the inverted band gaps that are the manifestation of a topologically non-trivial character. For the description of surfaces of topological insulators as well as interfaces and heterostructures, I will introduce a method based on Wannier functions to construct very accurate, first-principles tight-binding Hamiltonians. Finally, I will outline future plans of my group in the fields of magnetic topological insulators and non-Hermitian topological matter.