Observation of a topological drumhead surface state in a topological semimetal*

Topological non-trivial states of matter manifest unique electronic structures, including 3D Dirac line nodes and topological surface states. One notable topological surface states, drumhead surface states, have received significant attention because of its unique flat dispersion. Despite a large number of works, such a flat signature of drumhead states remains elusive. We will present the experimental evidence of nearly-flat drumhead surface states in a topological semimetal BaAl₄ using angle-resolved photoemission spectroscopy and discuss these results in terms of correlations.