Abstract:

Topology has been established as a powerful tool for the understanding of electronic structure in crystalline matter. In this talk, I will report on recent spectroscopic studies on two types of topological materials, Weyl semimetals (WSM) and magnetic topological insulators (MTI).

Weyl nodes are topologically protected intersections between non-degenerate electron bands. At these special points in momentum space the Bloch wave functions show a special behavior: in the bulk the Weyl nodes constitute monopoles of Berry flux and at the surface their projections define the termination points of Fermi-arc surface states. I will discuss how these intricate properties can be addressed experimentally by the use of dichroism in angle-resolved photoemission spectroscopy (ARPES) .

MTI are materials that combine a topological electronic band structure and magnetic order. I will show how ferromagnetic extension of a topological insulator in epitaxially grown heterostructures induces a large and robust gap in the surface state, resulting from broken time-reversal symmetry below the Curie temperature.