Paper detail

Low-temperature thermal expansion of the topological material candidates $β$-PtBi$_2$ and $β$-Bi$_2$Pd

We report on the low-temperature ($T <$ 120 K) thermal expansion of the bismuth-based topological semimetal $β$-PtBi$_2$ and topological superconductor $β$-Bi$_2$Pd candidates. The linear thermal-expansion coefficient of tetragonal $β$-Bi$_2$Pd shows a pronounced anisotropy between the $a$- and $c$-axis while the volume thermal-expansion coefficient $α_V$($β$-Bi$_2$Pd) is considerable larger than $α_V$($β$-PtBi$_2$). The coefficient $α_V$($β$-PtBi$_2$) nearly matches the experimental specific heat, from which a Debye temperature $θ_D =$ 199 K is obtained. On the other hand, $α_V$($β$-Bi$_2$Pd) reasonably fits the Debye model with $θ_D =$ 138 K, extracted from the low-temperature specific heat. An almost constant Grüneisen parameter $Γ\approx$ 2 is obtained for both compounds. No magnetostriction is observed in any of both compounds up to $μ_0 H =$ 16 T. We compare our results with other Bi-based topological materials.