Electrical and thermal transport properties of kagome metals $A$Ti${}_3$Bi${}_5$ ($A$ = Rb, Cs)

Abstract

We report electrical and thermal transport properties of single crystalline kagome metals $A$Ti${}_3$Bi${}_5$ ($A$ = Rb, Cs). Different from the structural similar kagome superconductors $A$V${}_3$Sb${}_5$, no charge density wave instabilities are found in $A$Ti${}_3$Bi${}_5$. At low temperatures below 5 K, signatures of superconductivity appear in $A$Ti${}_3$Bi${}_5$ as seen in magnetization measurements. However, bulk superconductivity is not evidenced by specific heat results. Similar to $A$V${}_3$Sb${}_5$, $A$Ti${}_3$Bi${}_5$ show nonlinear magnetic field dependence of the Hall effect below about 70 K, pointing to a multiband nature. Unlike $A$V${}_3$Sb${}_5$ in which phonons and electron-phonon coupling play important roles in thermal transport, the thermal conductivity in $A$Ti${}_3$Bi${}_5$ is dominated by electronic contributions. Moreover, our calculated electronic structure suggests that van Hove singularities are sitting well above the Fermi energy. Compared with $A$V${}_3$Sb${}_5$, the absence of charge orders in $A$Ti${}_3$Bi${}_5$ is closely associated with minor contributions from electron-phonon coupling and/or van Hove singularities.

8 pages, 5 figures,accepted for publication in Phys. Rev. B

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