Abstract:The lattice thermal conductivity, k L , of typical metallic and non-metallic crystals decreases rapidly with increasing temperature because phonons interact more strongly with other phonons than they do with electrons. Using first principles calculations, we show that k L can become nearly independent of temperature in metals that have nested Fermi surfaces and large frequency gaps between acoustic and optic phonons. Then, the interactions between phonons and electrons become much stronger than the mutual inte… Show more
“…2 a. Similar dips driven by the same selection rule occur in other cubic compounds such as BAs, BSb, 3C-SiC, diamond, c-BN, c-GaN, and c-AlN 5 , 12 as well as in certain transition metal carbides 36 . Fig.…”
Selection rules act to restrict the intrinsic anharmonic interactions between phonons in all crystals. Yet their influence on phonon propagation is hidden in most materials and so, hard to interrogate experimentally. Using ab initio calculations, we show that the otherwise invisible impact of selection rules on three-phonon scattering can be exposed through anomalous signatures in the pressure (P) and temperature (T) dependence of the thermal conductivities, κ, of certain compounds. Boron phosphide reveals such underlying behavior through an exceptionally sharp initial rise in κ with increasing P, which may be the steepest of any material, and also a peak and decrease in κ at high P. These features are in stark contrast to the measured behavior for many solids, and they occur at experimentally accessible conditions. These findings give a deep understanding of phonon lifetimes and heat conduction in solids, and motivate experimental efforts to observe the predicted behavior.
“…2 a. Similar dips driven by the same selection rule occur in other cubic compounds such as BAs, BSb, 3C-SiC, diamond, c-BN, c-GaN, and c-AlN 5 , 12 as well as in certain transition metal carbides 36 . Fig.…”
Selection rules act to restrict the intrinsic anharmonic interactions between phonons in all crystals. Yet their influence on phonon propagation is hidden in most materials and so, hard to interrogate experimentally. Using ab initio calculations, we show that the otherwise invisible impact of selection rules on three-phonon scattering can be exposed through anomalous signatures in the pressure (P) and temperature (T) dependence of the thermal conductivities, κ, of certain compounds. Boron phosphide reveals such underlying behavior through an exceptionally sharp initial rise in κ with increasing P, which may be the steepest of any material, and also a peak and decrease in κ at high P. These features are in stark contrast to the measured behavior for many solids, and they occur at experimentally accessible conditions. These findings give a deep understanding of phonon lifetimes and heat conduction in solids, and motivate experimental efforts to observe the predicted behavior.
“…(1) Anharmonic phonon interactions with other particles. In some systems, one should consider not only how phonons interact with other phonons but also with other particles, such as electron-phonon coupling [271,273], spin-phonon coupling [274,275], and phonon-spin-orbit coupling [276,277]. These complicated correlations will jointly induce many novel properties.…”
Anharmonic lattice vibrations play pivotal roles in the thermal dynamics in condense matters and affect how the atoms interact and conduct heat. An in-depth understanding of the microscopic mechanism of phonon anharmonicity in condensed systems is critical for developing better functional and energy materials. In recent years, various novel behaviors in condense matters driven by phonon anharmonic effects were discovered, such as soft mode phase transition, negative thermal expansion (NTE), multiferroicity, ultralow thermal conductivity (κ), high thermal resistance, and high-temperature superconductivity. These properties have endowed anharmonicity with many promising applications and provided remarkable opportunities for developing "Anharmonicity Engineering"-regulating heat transport towards excellent performance in materials. In this work, we review the recent development of studies on phonon anharmonic effect and summarize its origin, mechanism, research methods, and applications. Besides, the remaining challenges, future trends, and prospects of phonon anharmonicity are also discussed.
“…2,3 However, NbC and W have been identified as exceptions by very recent calculations. 4,5 In those materials, electron-phonon scattering is comparable to or stronger than phonon-phonon scattering, leading to an anomalously weak temperature dependence of the lattice thermal conductivity (κ ph ). Likewise, the unusual temperature dependence of κ ph in NbSe 3 nanowires below the charge-density-wave transition temperature was found to be related to electron-phonon coupling.…”
It was recently found that the anharmonic phonon-phonon scattering in tungsten is extremely weak at high frequencies, leading to a predominance of electron-phonon scattering and consequently anomalous phonon transport behaviors. In this work, we calculate the phonon linewidths of W along high-symmetry directions from first principles. We find that the weak phonon-phonon scattering can be traced back to two factors. The first is the triple degeneracy of the phonon branches at the P and H points, a universal property of elemental body-centered-cubic (bcc) structures. The second is a relatively isotropic character of the phonon dispersions. When both are met, phonon-phonon scattering rates must vanish at the P and H points. The weak phonon-phonon scattering feature is also applicable to Mo and Cr. However, in other elemental bcc substances like Na, the isotropy condition is violated due to the unusually soft character of the lower transverse acoustic phonon branch along the Γ-N direction, opening emission channels and leading to much stronger phonon-phonon scattering. We also look into the distributions of electron meanfree paths (MFPs) at room temperature in tungsten, which can help engineer the resistivity of nanostructured W for applications such as interconnects.
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