An ab initio study of β−As2Te3 (R¯3m symmetry) at hydrostatic pressures shows that this compound is a trivial small band-gap semiconductor at room pressure that undergoes a quantum topological phase transition to a 3D topological Dirac semimetal around 2 GPa. At higher pressures, the band gap reopens and again decreases above 4 GPa. Our calculations predict an insulator-metal transition above 6 GPa due to the closing of the band gap, with strong topological features persisting between 2 and 10 GPa with Z4=3 topological index. By investigating the lattice thermal conductivity (κL), we observe that close to room conditions κL is very low, either for the in-plane and the out-of-plane axis, with 0.098 and 0.023Wm−1K−1, respectively. This effect occurs due to the presence of two low-frequency optical modes, namely Eu and Eg, which increase the phonon-phonon scattering rate. Therefore, our results suggest that ultralow lattice thermal conductivities, which enable highly efficient thermoelectric materials, can be engineered in systems that are close to a structural instability derived from phonon Kohn anomalies. At higher pressures, the values of the in- and out-of-plane thermal conductivities not only increase in magnitude, but also approximate in value as the layered character of the compound decreases.

This research was supported by the European Union Horizon 2020 research and innovation programme under Marie Sklodowska-Curie Grant No. 785789-COMEX and Project No. NORTE-01-0145-FEDER-022096, Network of Extreme Conditions Laboratories (NECL), financed by FCT and cofinanced by NORTE 2020, through the programme Portugal 2020 and FEDER. Authors also thank the financial support of the Generalitat Valenciana under Project PROMETEO 2018/123-EFIMAT and of the Agencia Española de Investigación under Projects No. MAT2016-75586-C4-2/4-P, No. FIS2017-2017-83295-P, and No. PID2019-106383GB-C42, as well as the MALTA Consolider Team research network under Project No. RED2018-102612-T. Additionally, authors acknowledge the computer resources at MareNostrum with technical support provided by the Barcelona Supercomputing Center (QCM-2019-1-0032/37).

Peer reviewed