Superconducting, Topological, and Transport Properties of Kagome Metals CsTi ₃ Bi ₅ and RbTi ₃ Bi ₅

Abstract

The recently discovered ATi₃Bi₅ (A=Cs, Rb) exhibit intriguing quantum phenomena including superconductivity, electronic nematicity, and abundant topological states. ATi₃Bi₅ present promising platforms for studying kagome superconductivity, band topology, and charge orders in parallel with AV₃Sb₅. In this work, we comprehensively analyze various properties of ATi₃Bi₅ covering superconductivity under pressure and doping, band topology under pressure, thermal conductivity, heat capacity, electrical resistance, and spin Hall conductivity (SHC) using first-principles calculations. Calculated superconducting transition temperature (<i>T</i>_c) of CsTi₃Bi₅ and RbTi₃Bi₅ at ambient pressure are about 1.85 and 1.92 K. When subject to pressure, <i>T</i>_c of CsTi₃Bi₅ exhibits a special valley and dome shape, which arises from quasi-two-dimensional compression to three-dimensional isotropic compression within the context of an overall decreasing trend. Furthermore, <i>T</i>_c of RbTi₃Bi₅ can be effectively enhanced up to 3.09 K by tuning the kagome van Hove singularities (VHSs) and flat band through doping. Pressures can also induce abundant topological surface states at the Fermi energy (<i>E</i>_F) and tune VHSs across <i>E</i>_F. Additionally, our transport calculations are in excellent agreement with recent experiments, confirming the absence of charge density wave. Notably, SHC of CsTi₃Bi₅ can reach up to 226<i>ℏ</i> ·(e· Ω ·cm)^-1 at <i>E</i>_F. Our work provides a timely and detailed analysis of the rich physical properties for ATi₃Bi₅, offering valuable insights for further experimental verifications and investigations in this field.