Anomalous thermal expansion of Sb$_2$Te$_3$ topological insulator

We have investigated the temperature dependence of the linear thermal expansion along the hexagonal c axis ($ΔL$), in-plane resistivity ($ρ$), and specific heat ($C_p$) of the topological insulator Sb$_2$Te$_3$ single crystal. $ΔL$ exhibits a clear anomaly in the temperature region 204-236 K. The coefficient of linear thermal expansion $α$ decreases rapidly above 204 K, passes through a deep minimum at around 225 K and then increases abruptly in the region 225-236 K. $α$ is negative in the interval 221-228 K. The temperature dependence of both $α$ and $C_p$ can be described well by the Debye model from 2 to 290 K, excluding the region around the anomaly in $α$.

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