Fig. 1: Fermi surface and calculated band structures of CsTi3Bi5.
a Schematic pristine crystal structure of CsTi3Bi5. b Top view of the crystal structure with a two-dimensional kagome lattice of titanium. c Three-dimensional Brillouin zone with high-symmetry points and high-symmetry momentum lines marked. d Fermi surface mapping of CsTi3Bi5 measured at a temperture of 20 K. It is obtained by integrating the spectral intensity within 10 meV with respect to the Fermi level and symmetrized assuming six-fold symmetry. Five Fermi surface sheets are clearly observed and quantitatively shown in e. Three Fermi surface sheets are around the Brillouin zone center Γ marked as α (orange line), β (green line) and γ1 (light blue line). One Fermi surface is around the K point marked as γ2 (blue line) and one is around the M point marked as δ (dark blue line). f Calculated band structure along high-symmetry directions without considering SOC. Different colors represent different orbital components of Ti3d. g Same as (f) but considering SOC. The flat band (FB), two saddle points (VHS1 and VHS2) and a Dirac point (DP) are marked by arrows. To make a better comparison with measured results, the Fermi level referred to as EF(Exp.) is shifted downwards by 90 meV, as shown by the dashed lines in (f, g). h Calculated three-dimensional Fermi surface based on the first principle DFT calculations. The Fermi surface sheets are quite two dimensional. The calculated Fermi surface at EF(Exp.) and kz = 0 is shown in (i). The measured Fermi surface (d) shows an excellent agreement with the calculated one (i).
