Transport in Metals: Effect of the Nonequilibrium Phonons

Bailyn, M.

doi:10.1103/physrev.112.1587

Cited by 101 publications

(39 citation statements)

References 12 publications

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“…S3). It has been inferred that the saturation effect is associated with the interaction of increased electrons on phonons (7,9), but the interpretation is often vague due to the use of the variational approach (26) and the lack of quantitative evaluation. By performing first-principles simulation, we clarify the reason of the phonon drag reduction as the shortening of phonon mean free paths by electron scatterings and clearly show that the inclusion of this scattering mechanism leads to a good agreement of the phonon drag with the experiment Circles and squares are taken from the experiment (8).…”

Section: Resultsmentioning

confidence: 99%

“…An exact description of the phonon drag effect requires the solution of coupled electron-phonon Boltzmann transport equations (BTEs) with accurate matrix elements of various scattering processes (most importantly, the electron-phonon scattering and phonon-phonon scattering). Early theoretical works (1,5,7,26) attempted to concurrently solve the coupled electron-phonon BTEs mostly using a variational approach (1). Although reasonable agreements with experiments were achieved (27,28), the calculations were limited to the lowest orders of the trial functions for the variational method and assumed simplified scattering models, which lack predictive power due to the large number of adjustable parameters involved and make the interpretation of the calculated results less intuitive.…”

Section: Significancementioning

confidence: 99%

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Ab initio optimization of phonon drag effect for lower-temperature thermoelectric energy conversion

Zhou

Liao

Qiu

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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Although the thermoelectric figure of merit zT above 300 K has seen significant improvement recently, the progress at lower temperatures has been slow, mainly limited by the relatively low Seebeck coefficient and high thermal conductivity. Here we report, for the first time to our knowledge, success in first-principles computation of the phonon drag effect-a coupling phenomenon between electrons and nonequilibrium phonons-in heavily doped region and its optimization to enhance the Seebeck coefficient while reducing the phonon thermal conductivity by nanostructuring. Our simulation quantitatively identifies the major phonons contributing to the phonon drag, which are spectrally distinct from those carrying heat, and further reveals that although the phonon drag is reduced in heavily doped samples, a significant contribution to Seebeck coefficient still exists. An ideal phonon filter is proposed to enhance zT of silicon at room temperature by a factor of 20 to ∼0.25, and the enhancement can reach 70 times at 100 K. This work opens up a new venue toward better thermoelectrics by harnessing nonequilibrium phonons.phonon drag | nonequilibrium phonon | electron phonon interaction | thermoelectrics | nanocluster scattering I n metals and semiconductors, lattice vibration-, or phonon-, induced electron scattering has a major influence on electronic transport properties (1). The strength of the electron-phonon interaction (EPI) depends on the distribution of electron and phonon populations. The EPI problem was first studied by Bloch (2), who assumed the phonons to be in equilibrium (so-called Bloch condition) when calculating the scattering rates of electrons caused by EPI, because of the frequent phonon-phonon Umklapp scattering. This assumption is widely adopted for the determination of electronic transport properties at higher temperatures (1, 3), including the electrical conductivity and the normal ("diffusive") Seebeck coefficient. Below the Debye temperature, however, the nonequilibrium phonons become appreciable because the phonon-phonon Umklapp scatterings are largely suppressed, and this assumption becomes questionable. The significance of nonequilibrium phonons on the Seebeck coefficient was first recognized by Gurevich (4). The experimental evidence given later (5, 6) clearly showed an "anomalous" peak of the Seebeck coefficient at around 40 K in germanium. To address this unusual observation, Herring proposed that the nonequilibrium phonons can deliver excessive momenta to the electrons via the EPI (7). This process generates an extra electrical current in the same direction as the heat flow, as if the electrons were dragged along by phonons. Therefore, this effect has been dubbed "phonon drag" (7), which makes itself distinct from the normal (diffusive) Seebeck effect. Subsequent explorations (8-13) revealed that this effect exists in various material systems. In particular, it has been suggested that phonon drag is responsible for the extremely high Seebeck coefficient S = −4,500 μV/K experimentally found i...

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Section: Resultsmentioning

confidence: 99%

Section: Significancementioning

confidence: 99%

Ab initio optimization of phonon drag effect for lower-temperature thermoelectric energy conversion

Zhou

Liao

Qiu

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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“…Therefore it has been dubbed the phonon drag effect [33,39,40]. We will have more discussions on this effect in section 4.…”

Section: Electron-phonon Interactionmentioning

confidence: 99%

“…Under the linearized BTE formalism, it can be shown by using the Golden Rule that the collision terms (Eq. (5)) due to the electron-phonon interaction take the following form [33] , , ,…”

Section: Electron-phonon Interactionmentioning

confidence: 99%

First-principles calculations of thermal, electrical, and thermoelectric transport properties of semiconductors

Zhou

Liao

Chen

2016

Semicond. Sci. Technol.

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Transport properties of semiconductors are keys to the performance of many solid-state devices (transistors, data storage, thermoelectric cooling and power generation devices, etc.).Understanding of the transport details can lead to material designs with better performances. In recent years simulation tools based on first-principles calculations have been greatly improved, being able to obtain the fundamental ground state properties of materials (such as band structure and phonon dispersion) accurately. Accordingly, methods have been developed to calculate the transport properties based on an ab initio approach. In this review we focus on the thermal, electrical, and thermoelectric transport properties of semiconductors, which represent the basic transport characteristics of the two degrees of freedom in solids -electronic and lattice degrees of freedom.Starting from the coupled electron-phonon Boltzmann transport equations, we illustrate different scattering mechanisms that change the transport features and review the first-principles approaches that solve the transport equations. We then present the first-principles results on the thermal and electrical transport properties of semiconductors. The discussions are grouped based on different scattering mechanisms including phonon-phonon scattering, phonon scattering by equilibrium electrons, carrier scattering by equilibrium phonons, carrier scattering by polar optical phonons, scatterings due to impurities, alloying and doping, and phonon drag effect. We show how the first-principles methods allow one to investigate the transport properties with unprecedented details and also offer new insights to the electron and phonon transport. Current status of the simulation is mentioned when appropriate and some of the future directions are also discussed.

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“…Almost all of the earlier theoretical investigations for analyzing the diffusion [3,[15][16][17] and phonon drag [7][8][9]18] components of the thermoelectric power in macroscopic systems are based on the Boltzmann equation. In these works, the weakly nonuniform systems under the linear transport conditions are considered in the absence of external electric field and in the presence of lattice temperature gradient.…”

Section: Introductionmentioning

confidence: 99%

Thermoelectric power of nondegenerate Kane semiconductors under the conditions of mutual electron-phonon drag in a high electric field

et al. 2002

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The thermoelectric power of nondegenerate Kane semiconductors with due regard for the electron and phonon heating, and their thermal and mutual drags is investigated. The electron spectrum is taken in the Kane two-band form. It is shown that the nonparabolicity of electron spectrum significantly influences the magnitude of the thermoelectric power and leads to a change of its sign and dependence on the heating electric field. The field dependence of the thermoelectric power is determined analytically under various drag conditions.

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Transport in Metals: Effect of the Nonequilibrium Phonons

Cited by 101 publications

References 12 publications

Ab initio optimization of phonon drag effect for lower-temperature thermoelectric energy conversion

Ab initio optimization of phonon drag effect for lower-temperature thermoelectric energy conversion

First-principles calculations of thermal, electrical, and thermoelectric transport properties of semiconductors

Thermoelectric power of nondegenerate Kane semiconductors under the conditions of mutual electron-phonon drag in a high electric field

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