Exotic weak topological state in RhBi2

In contrast to the ubiquity of strong topological insulators, material realizations of weak topological insulators (TIs) remain largely elusive due to the inherent challenge of detecting their non-trivial surface states. The tailored synthesis of new materials is a promising path to reduce the experimental gap between strong and weak TIs, and can also lead to the discovery of novel quantum phenomena. Combining material synthesis, ARPES measurements, and analytical modeling, we report the discovery of a weak topological insulating state in triclinic RhBi₂. In this talk, we show that the low crystal symmetry -1 of this material allows for additional exotic features in the non-trivial surface state dispersion. In particular, two saddle points develop in the proximity of the surface Dirac cone, leading to a van Hove singularity in the surface density of states that is expected to dramatically enhance the effect of electronic interactions and potentially drive the systems towards many-body instabilities. As an example, we discuss how surface superconductivity is favored in the weak TI surface state of RhBi₂ as the chemical potential is tuned across the van Hove singularity. The proximity of saddle and Dirac points to the Fermi level makes RhBi₂ is a promising platform to investigate the interplay between electronic correlations and topological surface states.