Electrical and thermal transport properties of the kagome metals ATi3Bi5(A=Rb,Cs)

We report electrical and thermal transport properties of single-crystalline kagome metals $A{\text{Ti}}_{3}{\text{Bi}}_{5}\phantom{\rule{4pt}{0ex}}(A=\text{Rb},\phantom{\rule{4pt}{0ex}}\mathrm{Cs})$. Different from the structrually similar kagome superconductors $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$, no charge density wave instabilities are found in $A{\mathrm{Ti}}_{3}{\mathrm{Bi}}_{5}$. At low temperatures below 5 K, signatures of superconductivity appear in $A{\mathrm{Ti}}_{3}{\mathrm{Bi}}_{5}$ as seen in magnetization measurements. However, bulk superconductivity is not evidenced by specific heat results. Similar to $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}, A{\mathrm{Ti}}_{3}{\mathrm{Bi}}_{5}$ show a nonlinear magnetic field dependence of the Hall effect below about 70 K, pointing to a multiband nature. Unlike $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$ in which phonons and electron-phonon coupling play important roles in thermal transport, the thermal conductivity in $A{\mathrm{Ti}}_{3}{\mathrm{Bi}}_{5}$ is dominated by electronic contributions. Moreover, our calculated electronic structures of ${\mathrm{ATi}}_{3}{\mathrm{Bi}}_{5}$ suggest that van Hove singularities are sitting well above the Fermi energy. Compared with $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$, the absence of charge orders in $A{\mathrm{Ti}}_{3}{\mathrm{Bi}}_{5}$ is closely associated with minor contributions from electron-phonon coupling and/or van Hove singularities.