Superconducting, topological and transport properties of kagome metals CsTi$ _{3} $Bi$ _{5} $ and RbTi$ _{3} $Bi$ _{5} $

TL;DR

This study comprehensively investigates the superconducting, topological, and transport properties of kagome metals CsTi$_{3}$Bi$_{5}$ and RbTi$_{3}$Bi$_{5}$, revealing pressure and doping effects on superconductivity and topological states.

Contribution

It provides the first detailed analysis of how pressure and doping influence superconductivity and topological features in ATi$_3$Bi$_5$ kagome metals, combining first-principles calculations with experimental validation.

Findings

Superconducting transition temperatures are approximately 1.85K for CsTi$_3$Bi$_5$ and 1.92K for RbTi$_3$Bi$_5$ at ambient pressure.

Pressure induces a non-monotonic T_c behavior, including a valley and dome shape for CsTi$_3$Bi$_5$.

Doping can enhance RbTi$_3$Bi$_5$'s T_c up to 3.09K by tuning van Hove singularities and flat bands.

Abstract

The recently discovered ATi$_3$Bi$_5$ (A=Cs, Rb) exhibit intriguing quantum phenomena including superconductivity, electronic nematicity, and abundant topological states, which provide promising platforms for studying kagome superconductivity, band topology, and charge orders. In this work, we comprehensively study various properties of ATi$_3$Bi$_5$ including 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 ($\mathrm{ T_{c}}$) of CsTi$_3$Bi$_5$ and RbTi$_3$Bi$_5$ at ambient pressure are about 1.85 and 1.92K. When subject to pressure, $\mathrm{ T_{c}}$ of CsTi$_3$Bi$_5$ exhibits a special valley and dome shape, which arises from quasi-two-dimensional to three-dimensional isotropic compression within the context of an overall decreasing trend. Furthermore, $\mathrm{ T_{c}}$ of RbTi$_3$Bi$_5$ can be effectively enhanced up to 3.09K by tuning the kagome van Hove singularities (VHSs) and flat band through doping. Pressure can also induce abundant topological surface states at the Fermi energy ($\mathrm{E}_{\mathrm{F}}$) and tune VHSs across $\mathrm{E}_{\mathrm{F}}$. Additionally, our transport calculations are in excellent agreement with recent experiments, confirming the absence of charge density wave. Notably, SHC of CsTi$_3$Bi$_5$ can reach as large as 226$ \hbar\cdot (e\cdot \Omega \cdot cm) ^{-1} $ at $\mathrm{E}_{\mathrm{F}}$. Our work provides a timely and detailed analysis of the rich physical properties for ATi$_3$Bi$_5$, offering valuable insights for further explorations and understandings on these intriguing superconducting materials.