β−As2Te3 : Pressure-induced three-dimensional Dirac semimetal with ultralow room-pressure lattice thermal conductivity

Abstract

An ab initio study of β-As 2 Te 3 (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 Z 4 = 3 topological index. By investigating the lattice thermal conductivity (κ L ), we observe that close to room conditions κ L is very low, either for the in-plane and the out-of-plane axis, with 0.098 and 0.023 Wm −1 K −1 , respectively. This effect occurs due to the presence of two low-frequency optical modes, namely E u and E g , 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.

Experimental and theoretical study of β-As2Te3under hydrostatic pressure

“…30–33 Among theoretical studies of β-As 2 Te 3 , a figure of merit ( ZT ) of 0.7 has been predicted for β-As 2 Te 3 , 25 which is of the order of the ZT values of the well-known thermoelectric material α-Bi 2 Te 3 . 4 In the same context, a very small lattice thermal conductivity, κ L , has been predicted for β-As 2 Te 3 , 27,29 which has been experimentally confirmed. 15,17 For these calculations, the electronic band structure of β-As 2 Te 3 has been thoroughly studied, and spin–orbit coupling (SOC) has been found to be an essential requirement to obtain a good theoretical description of the electronic band structure as well as of the TE and TI properties.…”

“…Despite very interesting properties have been predicted in several theoretical studies of the β phase even at HP, 24–29 no experimental HP study of the β phase has been conducted yet, to our knowledge. Experimental HP studies have only explored the behavior of the α phase and glassy As 2 Te 3 .…”

“…Calculations have shown that β-As 2 Te 3 undergoes a topological quantum phase transition (TQPT) under uniaxial strain near 1.7 GP 28 and under hydrostatic pressure near 2 GPa due to the closing of the direct bandgap at the Γ point. 29 Around 2 GPa, β-As 2 Te 3 becomes a 3D topological Dirac semimetal with a single Dirac cone in its electronic structure at the Γ point. Above 2 GPa, the bandgap reopens, and β-As 2 Te 3 becomes a 3D TI, as isostructural Bi 2 Se 3 , Sb 2 Te 3 , and Bi 2 Te 3 .…”

“…15,17 For these calculations, the electronic band structure of β-As 2 Te 3 has been thoroughly studied, and spin–orbit coupling (SOC) has been found to be an essential requirement to obtain a good theoretical description of the electronic band structure as well as of the TE and TI properties. In particular, according to the most recent and accurate calculations, 29 β-As 2 Te 3 is predicted to be a trivial insulator with a very narrow (0.3 eV) indirect bandgap near the Z point. Calculations have shown that β-As 2 Te 3 undergoes a topological quantum phase transition (TQPT) under uniaxial strain near 1.7 GP 28 and under hydrostatic pressure near 2 GPa due to the closing of the direct bandgap at the Γ point.…”

“…Above 2 GPa, the bandgap reopens, and β-As 2 Te 3 becomes a 3D TI, as isostructural Bi 2 Se 3 , Sb 2 Te 3 , and Bi 2 Te 3 . 29 The different behavior of β-As 2 Te 3 is due to its smaller SOC, so uniaxial stress or hydrostatic pressure is needed to transform this compound from a trivial insulator to a TI by helping to decrease the bandgap and allow SOC to induce a band inversion. 28,29…”