Energy transport in glasses due to phonon hopping: Lifetime and ac behavior

Damker, T.; Böttger, H.; Bryksin, V. V.

doi:10.1103/physrevb.59.8626

Cited by 9 publications

(3 citation statements)

References 20 publications

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“…This observation is in quantitative agreement with the results of the Raman measurements reported by Scholten et al Also, in different types of experiment, indications for the existence of such long-lived phonons in amorphous solids have been found. [23][24][25] Theoretical descriptions that are consistent with the occurrence of lifetimes of the order of magnitude observed in the experiments are the fracton model 3 and the hopping model by Damker et al 27 Both models involve the localization of the major part of the vibrational modes in a-Si and the assumption that the anharmonic decay of localized into localized vibrations can be neglected. In contrast, numerical simulations based on the diffuson model predict that most of the vibrational excitations in a-Si are extended.…”

Section: Phonon Decay In Amorphous Siliconmentioning

confidence: 70%

Phonon generation and decay in hydrogenated amorphous silicon

2000

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We report on investigations of the temporal evolution of nonequilibrium phonon populations in hydrogenated amorphous silicon held at 1.8 K. Two types of a-Si:H were examined, one grown by plasma enhanced chemical vapor deposition ͑PE͒ and one by hot-wire assisted chemical vapor deposition ͑HW͒. Phonons were created during the relaxation and recombination of optically excited charge carriers, and detected by means of pulsed anti-Stokes Raman spectroscopy. In the same setup, pulsed luminescence experiments were performed, under identical experimental conditions. The temporal shape of the Raman signals turned out to be determined both by the electronic processes responsible for the phonon generation and by the anharmonic decay of the excited phonon population itself. In the PE films we observed a slowly decaying (ӷ100 ns͒ contribution to the Raman signal, which was not present in the HW layers. We propose a model to explain this slow background as resulting from laser-induced fast nonradiative recombination of mobile with localized charge carriers. The results of the pulsed luminescence experiments support our model. In addition, phonon decay times were observed to be the same in all samples: decay times of ϳ70 ns were obtained for LA-and TO-like vibrations, whereas TA-like vibrations decayed faster (Ͻ10 ns͒ than could be resolved with the experimental setup. We propose that the extreme longevity of the LA and TO phonons is related to the microstructure of amorphous silicon.

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Section: Phonon Decay In Amorphous Siliconmentioning

confidence: 70%

Phonon generation and decay in hydrogenated amorphous silicon

2000

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“…Excitations showing such characteristics are known to dominate thermal transport at frequencies about 1 THz and temperatures well above the 'plateau' region. In other words, the most widely accepted picture of energy transport in disordered matter at high temperatures portrays heat as carried by thermally activated hopping resulting from anharmonic interactions between long-wavelength phonons and localized vibrational states (Fabian and Allen 1999, Damker et al 1999. However, the nature of such localized states and their role in thermal transport resists a full quantitative understanding.…”

Section: Discussionmentioning

confidence: 99%

Dynamical aspects of disorder in condensed matter

2003

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This work reviews progress in the field of the dynamics of disordered condensed matter, encompassing materials where at least one component lacks either rotational or translational long-range order. Systems in thermodynamic equilibrium as well as those where some aspect of the disorder is frozen into a glassy state are discussed. The most relevant experimental methods are reviewed, as well as recent advances in computer simulation, which is becoming increasingly important in this field. Examples of recent applications of these techniques to study the various aspects of dynamical disorder are then provided. The final section highlights common features of the dynamics exhibited by different systems, and discusses prospects for the future development of the field.

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“…In order to explain the heat conductivity behavior of dielectric glassy systems at high temperatures, a transport mechanism has been put forward, which is based on hopping of vibrational fractons [4,5] or of Anderson-localized phonons [6]. Those models have been compared with relaxation experiphys.…”

Section: Discussionmentioning

confidence: 99%

Energy Space Diffusion of Hopping Excitations in Non-Equilibrium

Damker

Bryksin

2002

phys. stat. sol. (b)

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The effective medium theory of hopping by Bleibaum, Bö ttger and Bryksin is generalized to finite temperatures. Starting point is the system of rate equations for the (localized) site occupation numbers of a disordered system. An effective generalized Fokker-Planck equation is derived thereof, which contains terms describing diffusion in real space, as well as terms describing drift and diffusion in energy space. The corresponding effective medium is determined self-consistently. The theory describes the relaxation in a system of localized excitations, where transitions are possible by hopping. It considers the behavior at high temperatures, corresponding to nearest neighbor hopping. IntroductionThe model under consideration consists of a number of localized states, which interact anharmonically with extended states, so that transitions between the localized states are possible. One example is the hopping motion of electrons in band tails. Another one is the hopping of localized vibrational states, discussed at the end of this paper. Of central interest is the behavior of excitations of the localized subsystem over time, especially their relaxation after an initial excitation. Such excitations can spatially diffuse away, as well as undergo a ''diffusion" in energy space, which superficially contradicts energy conservation, but can effectively occur, since the ''missing" energy is transferred into the extended subsystem, which is treated as a heat bath. This implies, that relaxation processes within this subsystem must be very fast compared with relaxation in the localized subsystem.The temporal behavior of the localized states is assumed to be adequately described by linearized rate equations for the occupation numbers of those states. Thus, the particles are considered as non-interacting, and the basic transport is incoherent and Markovian. But, the equations for the effective medium will be non-Markovian.For this problem an effective medium theory has been put forward by Bleibaum et al. [1][2][3]. We generalize this theory to finite temperatures. In addition to the drift term in energy space, which is already considered in Ref.[3], here we also have to take into account a diffusion term in energy space. Additionally, we allow the excitations to have a finite life-time.

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Energy transport in glasses due to phonon hopping: Lifetime and ac behavior

Cited by 9 publications

References 20 publications

Phonon generation and decay in hydrogenated amorphous silicon

Phonon generation and decay in hydrogenated amorphous silicon

Dynamical aspects of disorder in condensed matter

Energy Space Diffusion of Hopping Excitations in Non-Equilibrium

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