Discovery of a weak topological insulating state and van Hove singularity in triclinic RhBi2
Recent experiments provide evidence for a new weak topological insulator with unusal dispersion features.
a, k ⋅ p model band dispersion around the Z point, revealing a nodal point, two saddle points and the almost-flat region of the lower energy band at slightly lower energies. The two saddle points at energy − 83 meV are responsible for the logarithmic divergence of the DOS. b Fermi surface plot of the ARPES intensity integrated within 10 meV of the chemical potential around the Z point. Dark areas mark location of the FS. c–f Calculated band dispersion along the vertical direction in (b) that is marked as red dashed lines (#1-3), respectively. f Calculated band dispersion along the horizontal direction in (b) that is marked as a blue dashed line (#4). Black arrows mark locations of band minimums. g–j ARPES data along the same cuts as in (c–f).
Time reversal symmetric (TRS) invariant topological insulators (TIs) fullfil a paradigmatic role in the field of topological materials, standing at the origin of its development. Apart from TRS protected strong TIs, it was realized early on that more confounding weak topological insulators (WTI) exist. WTIs depend on translational symmetry and exhibit topological surface states only in certain directions making it significantly more difficult to match the experimental success of strong TIs. We here report on the discovery of a WTI state in RhBi2 that belongs to the optimal space group P1¯, which is the only space group where symmetry indicated eigenvalues enumerate all possible invariants due to absence of additional constraining crystalline symmetries. Our ARPES, DFT calculations, and effective model reveal topological surface states with saddle points that are located in the vicinity of a Dirac point resulting in a van Hove singularity (VHS) along the (100) direction close to the Fermi energy (EF). Due to the combination of exotic features, this material offers great potential as a material platform for novel quantum effects.Discovery of a weak topological insulating state and van Hove singularity in triclinic RhBi2 Kyungchan Lee, Gunnar F. Lange, Lin-Lin Wang, Brinda Kuthanazhi, Thaís V. Trevisan, Na Hyun Jo, Benjamin Schrunk, Peter P. Orth, Robert-Jan Slager, Paul C. Canfield and Adam Kaminski, Nature Comm. 12, 1855 (2021)