Lattice instability and phonon lifetimes in Pb<sub>1-x</sub>Sn<sub>x</sub>Te alloys

Daughton, W J; Tompson, C. W.; Gürmen, E.

doi:10.1088/0022-3719/11/8/018

Cited by 18 publications

(6 citation statements)

References 16 publications

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“…In parallel, powerful ab initio computational techniques can be used to calculate the phonon dispersions, and can be compared directly with experiments.Here, we present a detailed mapping of the fourdimensional S(Q, E) of PbTe based on inelastic neutron scattering measurements on single-crystalline PbTe, and results of ab initio phonon calculations using density functional theory (DFT). While our measurements are in general agreement with previous reports [13][14][15], our more detailed investigations also reveal several new key features that directly relate to the origin of the low κ. In particular, our measurements of the temperature and wavevector dependences of the TO mode reveal previously unreported anomalies.…”

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confidence: 92%

Giant anharmonic phonon scattering in PbTe

et al. 2011

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Understanding the microscopic processes affecting the bulk thermal conductivity is crucial to develop more efficient thermoelectric materials. PbTe is currently one of the leading thermoelectric materials, largely thanks to its low thermal conductivity. However, the origin of this low thermal conductivity in a simple rocksalt structure has so far been elusive. Using a combination of inelastic neutron scattering measurements and first-principles computations of the phonons, we identify a strong anharmonic coupling between the ferroelectric transverse optic mode and the longitudinal acoustic modes in PbTe. This interaction extends over a large portion of reciprocal space, and directly affects the heat-carrying longitudinal acoustic phonons. The longitudinal acoustic-transverse optic anharmonic coupling is likely to play a central role in explaining the low thermal conductivity of PbTe. The present results provide a microscopic picture of why many good thermoelectric materials are found near a lattice instability of the ferroelectric type.

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confidence: 92%

Giant anharmonic phonon scattering in PbTe

et al. 2011

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“…1, the TO phonon dispersion exhibits a pronounced dip at the zone center, Γ, in both PbTe and SnTe, in agreement with the literature [20,[35][36][37][38][39][40]. It is important to note, though, that our measurements map χ 00 ðQ; ΩÞ, instead of just the position of intensity maxima.…”

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confidence: 89%

“…1, the TO phonon dispersion exhibits a pronounced dip at the zone center, Γ, in both PbTe and SnTe, in agreement with the literature. [19,[33][34][35][36][37][38] It is important to note, though, that our measurements map χ ′′ (Q, Ω ), instead of just the position of maxima in intensity. These maps reveal a strong broadening for the soft optical phonons at Γ in both materials, indicating short phonon lifetimes and large anharmonicity.…”

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confidence: 99%

Phonon Self-Energy and Origin of Anomalous Neutron Scattering Spectra in SnTe and PbTe Thermoelectrics

et al. 2014

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The anharmonic lattice dynamics of rock-salt thermoelectric compounds SnTe and PbTe are investigated with inelastic neutron scattering (INS) and first-principles calculations. The experiments show that, surprisingly, although SnTe is closer to the ferroelectric instability, phonon spectra in PbTe exhibit a more anharmonic character. This behavior is reproduced in first-principles calculations of the temperature-dependent phonon self-energy. Our simulations reveal how the nesting of phonon dispersions induces prominent features in the self-energy, which account for the measured INS spectra and their temperature dependence. We establish that the phase space for three-phonon scattering processes, combined with the proximity to the lattice instability, is the mechanism determining the complex spectrum of the transverse-optic ferroelectric mode

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“…A consequence is a strong intrinsic electron-phonon coupling 14,15 , which leads to a ferro-electric phase transition in SnTe 16,17 . One way to suppress the ferroelectric transition is to substitute Pb for Sn, and it has been estimated that the transition should hit 0 K for Pb y Sn 1−y Te with y ≈ 0.5 18 . At this Pb concentration the system becomes a TCI 19 .…”

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confidence: 99%

Unusual phonon density of states and response to the superconducting transition in the In-doped topological crystalline insulator Pb0.5Sn0.5Te

et al. 2018

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We present inelastic neutron scattering results of phonons in (Pb0.5Sn0.5)1−xInxTe powders, with x = 0 and 0.3. The x = 0 sample is a topological crystalline insulator, and the x = 0.3 sample is a superconductor with a bulk superconducting transition temperature Tc of 4.7 K. In both samples, we observe unexpected van Hove singularities in the phonon density of states at energies of 1-2.5 meV, suggestive of local modes. On cooling the superconducting sample through Tc, there is an enhancement of these features for energies below twice the superconducting-gap energy. We further note that the superconductivity in (Pb0.5Sn0.5)1−xInxTe occurs in samples with normal-state resistivities of order 10 mΩ cm, indicative of bad-metal behavior. Calculations based on density functional theory suggest that the superconductivity is easily explainable in terms of electron-phonon coupling; however, they completely miss the low-frequency modes and do not explain the large resistivity. While the bulk superconducting state of (Pb0.5Sn0.5)0.7In0.3Te appears to be driven by phonons, a proper understanding will require ideas beyond simple BCS theory.Topological insulators (TIs) represent an exotic state of matter in which the bulk is insulating but the surface is metallic 1,2 . The topological state is protected by the time-reversal symmetry 1 . By including a certain crystal point group symmetry instead of time reversal, topological crystalline insulators (TCIs), a state analogous to TIs, was also proposed 3,4 . In particular, it was predicted that compounds such as SnTe might be TCIs 5 , and the key features, including the inverted character of bands near the chemical potential 6,7 and surface states within the band gap that are protected from back-scattering 8,9 , were soon verified.These developments have also spurred renewed interest in topological superconductors, as such materials may exhibit gapless surface states that could be beneficial for quantum computing 1-3 . A common aspect of TCIs is strong spin-orbit coupling in the atomic states contributing to the valence and conduction bands, and this is a useful ingredient for obtaining the unusual pairing symmetry expected for a topological superconductor. Hence, there is interest in seeing whether doping TCIs can induce superconductivity with a topological nature. Indeed, one can make SnTe superconducting by introducing In, and a point-contact study found evidence of surface Andreev bound states 10 , though thermodynamic studies suggest a fully gapped superconducting state [11][12][13] .SnTe is a compound that has the rocksalt structure despite the fact that the component elements do not all form closed-shell ions. A consequence is a strong intrinsic electron-phonon coupling 14,15 , which leads to a ferro-electric phase transition in SnTe 16,17 . One way to suppress the ferroelectric transition is to substitute Pb for Sn, and it has been estimated that the transition should hit 0 K for Pb y Sn 1−y Te with y ≈ 0.5 18 . At this Pb concentration the system becomes a TCI 19 . Also, s...

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Lattice instability and phonon lifetimes in Pb_1-xSn_xTe alloys

Cited by 18 publications

References 16 publications

Giant anharmonic phonon scattering in PbTe

Giant anharmonic phonon scattering in PbTe

Phonon Self-Energy and Origin of Anomalous Neutron Scattering Spectra in SnTe and PbTe Thermoelectrics

Unusual phonon density of states and response to the superconducting transition in the In-doped topological crystalline insulator Pb0.5Sn0.5Te

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Lattice instability and phonon lifetimes in Pb1-xSnxTe alloys

Cited by 18 publications

References 16 publications

Giant anharmonic phonon scattering in PbTe

Giant anharmonic phonon scattering in PbTe

Phonon Self-Energy and Origin of Anomalous Neutron Scattering Spectra in SnTe and PbTe Thermoelectrics

Unusual phonon density of states and response to the superconducting transition in the In-doped topological crystalline insulator Pb0.5Sn0.5Te

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Product

Resources

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Lattice instability and phonon lifetimes in Pb_1-xSn_xTe alloys