Tunable van Hove singularity without structural instability in Kagome metal CsTi${}_3$Bi${}_5$

In Kagome metal CsV${}_3$Sb${}_5$, multiple intertwined orders are accompanied by both electronic and structural instabilities. These exotic orders have attracted much recent attention, but their origins remain elusive. The newly discovered CsTi${}_3$Bi${}_5$ is a Ti-based Kagome metal to parallel CsV${}_3$Sb${}_5$. Here, we report angle-resolved photoemission experiments and first-principles calculations on pristine and Cs-doped CsTi${}_3$Bi${}_5$ samples. Our results reveal that the van Hove singularity (vHS) in CsTi${}_3$Bi${}_5$ can be tuned in a large energy range without structural instability, different from that in CsV${}_3$Sb${}_5$. As such, CsTi${}_3$Bi${}_5$ provides a complementary platform to disentangle and investigate the electronic instability with a tunable vHS in Kagome metals.