Pressure-tuning topological phase transitions in Kagome superconductor CsTi_3Bi_5

Recently, the Kagome metal CsTi_3Bi_5 has exhibited several novel quantum properties similar to CsV_3Sb_5, such as nontrivial topology, double-dome superconductivity, and flat band features. However, CsTi_3Bi_5 lacks the charge-density wave (CDW) present in CsV_3Sb_5, making the study of its emergence of double-dome superconductivity a focus of research. In this work, we have identified an order parameter, the three-band Z_2 topological index, that can describe the superconducting phase diagram of CsTi_3Bi_5 under pressure. Its evolution with pressure follows the expected behavior for superconductivity. Furthermore, the results of the Fermi surface under pressure reveal the potential presence of a Lifshitz transition in the vicinity of the vanishing point of the superconducting temperature change with pressure in CsTi_3Bi_5. These results indicate that the superconducting behavior of CsTi_3Bi_5 under pressure is caused by changes in the electronic structure leading to alterations in the topological properties, provide new insights and approaches for understanding the superconducting phenomenon in Kagome metals.