KTH/Nordita/SU seminar in Theoretical Physics

Knots, topology and broken symmetries in quantum materials

by Emil Bergholtz (SU)



In this talk I will discuss how very basic questions like “under which conditions do two energy bands generically cross at a single point?” lead to an understanding of a number of remarkable effects recently observed in various materials. Most saliently, this includes phenomena related to emergent Weyl fermions whose condensed matter incarnations show both analogies with—and striking differences compared to—their elusive high-energy relatives. In particular, I will discuss Lorentz symmetry breaking terms leading to “type-II” Weyl fermions whose dispersion is strongly tilted in close analogy with the tilted light cone of a particle entering a black hole, as well as the bulk-boundary correspondence and Fermi arcs in light of exactly solvable lattice models.