Top PDF High Temperature Electron-Phonon and Magnon-Phonon Interactions

High Temperature Electron-Phonon and Magnon-Phonon Interactions

High Temperature Electron-Phonon and Magnon-Phonon Interactions

The investigation of magnon-phonon interactions at elevated temperatures in this thesis was motivated by recent studies of vibrational thermodynamics impacted by thermal magnetic disorder. Mauger et al. have observed through nuclear resonant inelastic x-ray scattering (NRIXS) measurements an anomalous thermal softening of phonons in bcc α-iron stronger than predicted by the QH model [7]. The strong deviation from the QH model tracked the rapid decrease in the magnetization of α-Fe [29] and the rise in magnetic entropy, as seen in the left panel of Fig. 1.5. The second-nearest-neighbor (2NN) longitudinal force constants associated with an abnormal 2NN exchange interaction [30] were observed to soften by 40 to 60% from 30 K to the Curie temperature. The sharp increase in the vibrational entropy from the magnon-phonon interaction was reported to help extend the stability of the bcc phase of iron well past its Curie temperature.
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Rapid change of superconductivity and electron-phonon coupling through critical doping in Bi-2212

Rapid change of superconductivity and electron-phonon coupling through critical doping in Bi-2212

qualitatively consistent with previous scanning tunneling microscope studies (20). Such a mode was also revealed in recent high resolution photoemission studies on similarly overdoped systems near the antinode (27). Surprisingly, the spectral weight associated with the dip, which reflects the EPC strength (24), abruptly grows between p ~ 0.22 and p ~ 0.19 (Fig. 2E). This, along with the similar behavior in doping dependent charge transport properties (28), cannot be explained by a simple chemical potential shift, which has yet to cross the band bottom at (π,0) (Fig. 2A). For comparison, the pre-depletion of the density of states (DoS) from the high temperature normal state to T c (ratio between the red and blue arrows in Fig. 2C, also see Fig. S6C) is plotted in Fig.
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Theory of Phonon- Phonon Interaction in Semiconductor Crystals

Theory of Phonon- Phonon Interaction in Semiconductor Crystals

Abstract:- An equation of motion technique of quantum dynamics and Dyson equation approach have been used to obtain Fourier transformed electron Green`s function in presence of isotopic impurity and anharmonicity Hamiltonian has been taken as a sum of harmonic part , electron part , defect part , electron phonon interaction part , anharmonic part .The anharmonicity has been taken upto quartic terms . The response function has been obtained responsible for electron phonon linewidth . At high temperature, an expression of electron density of states (EDOS) has been obtained according to different fields present in semiconductor continuum. An EDOS has also been influenced by perturbed mode energy .The effect on intensity of peaks with respect to temperature and different excitations has been undertaken in this framework.
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Engineering Phonon, Photon, Electron and Plasmon interactions in Silicon - Metal Nanocavitiies for Silicon Photonics and Thermoplasmonics

Engineering Phonon, Photon, Electron and Plasmon interactions in Silicon - Metal Nanocavitiies for Silicon Photonics and Thermoplasmonics

explored. Decade long research has opened up exciting possibilities; with silicon laser 5 and optical modulation being realized 6 , which could dramatically revolutionize the industry. To give some perspective, copper interconnects typically allow for a speed of ~100Mbits/sec and the best ones available can potentially go as fast as 10- 20Gbits/second 3 . Today silicon devices can modulate signals electro-optically and process data at speeds higher than that 7 . It can be used to process optical signals at speeds of 100Gbit/s and beyond 7 8 . Tbits/s speed is the next goal 9 and while the developments so far have been promising, there are still a variety of issues that need to be addressed. Silicon based photonic devices typically have large footprints (>10 μm). Hence they require higher operating powers; which along with their size-mismatch with electronic components limits their potential for ultra dense device integration. High manufacturing cost for high volume production, high heat generation originating from high power requirements further limit the applications. Moreover some silicon-germanium (or III-V) hybrid components are still required especially for applications as a lasing source, which further complicates the integration steps. Therefore, new advances in materials design, fundamental understanding of nanoscale optical physics and innovative optical engineering are required to solve this problem.
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The Phonon Thermodynamics of Iron and Cementite

The Phonon Thermodynamics of Iron and Cementite

[33]. All these modes soften anomalously with temperature. Softening of the modes on the Brillioun zone face between the H and P high symmetry points, most noticeably at 2/3 L[ξξξ], have been associated with the structural instability of the bcc lattice under pressure towards the hexagonal ω- phase. The dynamical precursors to the α-γ transition in Fe seem to originate with the softening of the [ξ,ξ,0] branch, which is much larger than the softening of the [ξ,ξ,ξ] branch that is characteristic of the structural ω-phase transition in the Group 4 bcc metals (Ti, Zr, Hf) [33, 34] and Cr [92] at elevated pressures. A large decrease in 2NN longitudinal forces was reported in bcc chromium at high temperatures, but Cr melts before the 2NN longitudinal force constant reaches the low values seen here for Fe [92]. The soft phonons shown in Fig. 6.8 begin to deviate from quasiharmonic behavior several hundred degrees below the magnetic transition, and continue to soften above the Curie temperature. This anomalous phonon softening occurs in the same temperature range as the rapid decrease in the magnetization of α-Fe [93]. Magnetic short range order has long been suspected of being important for the phonon thermodynamics of the paramagnetic phase [94], and recent DFT calculations that account for paramagnetic interactions have successfully predicted the phonon dynamics at these temperatures [86].
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Effect of growth temperature on the morphology and phonon properties of InAs nanowires on Si substrates

Effect of growth temperature on the morphology and phonon properties of InAs nanowires on Si substrates

obtain more understanding about the controlled growth of catalyst-free InAs NWs on Si, InAs NWs were grown at various temperatures ranging from 530°C to 570°C, i. e., 530°C for sample A, 550°C for sample B and 570°C for sample C. The morphology of InAs NWs was char- acterized by field emission scanning electron microscopy (S-4800, Hitachi, Tokyo, Japan) and high-resolution transmission electron microscopy (HRTEM, Tecnai F20, 200 keV; FEI, Eindhoven, Netherlands). Raman scatter- ing measurements were performed in backscattering geometry at room temperature with a Jobin Yvon HR800 confocal micro-Raman spectrometer (Horiba Ltd., Longjumeau, France). Scattering configuration z(x, x + y)z ( x [0 11], ¯ y [ 211], ¯ z [111] ) was adopted. The samples were excited by the 514.5 nm line of an Ar-ion laser to a 1 µm spot on the surface with an exci- tation power of 0.05 mW.
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Spin–lattice and electron–phonon coupling in 3d/5d hybrid Sr3NiIrO6

Spin–lattice and electron–phonon coupling in 3d/5d hybrid Sr3NiIrO6

we combine infrared and optical spectroscopies with high-field magnetization and first-principles calculations to explore the fundamental excitations of the lattice and related coupling processes including spin – lattice and electronphonon mechanisms. Magneto-infrared spectroscopy reveals spin – lattice coupling of three phonons that modulate the Ir environment to reduce the energy required to modify the spin arrangement. While these modes primarily affect exchange within the chains, analysis also uncovers important inter-chain motion. This provides a mechanism by which inter-chain interactions can occur in the developing model for ultra-high coercivity. At the same time, analysis of the on-site Ir 4 + excitations reveals vibronic coupling and extremely large crystal fi eld parameters that lead to a t 2g -derived low-spin state for Ir. These fi ndings highlight the spin – charge – lattice
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Electron-phonon relaxation rates and optical gain in a quantum cascade laser in a magnetic field

Electron-phonon relaxation rates and optical gain in a quantum cascade laser in a magnetic field

The last decade has witnessed fast progress in the field of unipolar semiconductor quantum cascade lasers sQCLsd, which are very promising candidates for practical sources of radiation, particularly in the midinfrared spectral range. 1–7 Considerable output power, room-temperature operation, as well as the ability to get a range of lasing wavelengths using the same material system, opens up a number of potential applications for these devices, such as trace gas detection, polution control, medical diagnostics, optical communica- tions in high-transparency atmospheric windows, etc. 4
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Observation of Electron Phonon Couplings and Fano Re sonances in Epitaxial Bilayer Graphene

Observation of Electron Phonon Couplings and Fano Re sonances in Epitaxial Bilayer Graphene

perature using a Bruker Vertex 80 v FTIR spectrometer. Raman maps were performed using a Renishaw inVia Raman Microscope. A 532 nm Nd:YAG laser was used as a source of excitation. Our optical measurements were carried out for non-gated bilayer graphene and therefore, thus, our results differ from the ones published before. For four samples, graphene layers were grown by the CVD method at 1600˚C [18] and for one sample (sample 1275) by the Si sublimation method at 1600˚C under argon pressure. In both growth methods, semi-insulating on-axis 4H-SiC(0001) have been used. The intercalation of hydrogen under a buffer layer was performed at a rela- tively high temperature in the 1000˚C - 1100˚C range. Hydrogenated samples were cooled down in an argon and hydrogen atmosphere. In addition one n-type bilayer graphene sample for comparison was measured as well (sample 1637).
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PHONON PHONON INTERACTION IN RAMAN SCATTERING OF GERMANIUM

PHONON PHONON INTERACTION IN RAMAN SCATTERING OF GERMANIUM

Germanium has diamond type structure. It has two identical atoms in primitive unit cell. An equation of motion technique of quantum dynamics has been applied to develop the theory of Raman spectra of germanium. An expression for electron phonon linewidth and electron phonon shift has been obtained. It is established fact that at high temperature limit when anharmonic effects are dominant, the contributions of harmonic field, localized field, electron electron interaction field are feeble. It has been found that at high temperature limit, cubic and quartic parts of electron phonon linewidth and electron phonon shift have been matched with the Balkanski et al. model for linewidh and shift at high temperature. An analysis of first order Raman spectra of germanium has been carried out on taking anharmonicity upto quartic terms.
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Optimal electron, phonon, and magnetic characteristics for low energy thermally induced magnetization switching

Optimal electron, phonon, and magnetic characteristics for low energy thermally induced magnetization switching

increases in order to provide the same energy. This is in agreement with the theoretical prediction by Barker et al., 12 where it is proven that a minimum amount of extra energy from the laser is necessary to excite both the ferro- and antiferro-magnetic like magnon branches, which ultimately drives the magnetization reversal. This extra energy is more efficiently pumped to the spin system if the electron tempera- ture remains high for longer times. It remains a challenge to find ferrimagnetic materials that demonstrate TIMS but have low values of the electron-phonon coupling; however, still little is know about the precise value of the electron-phonon coupling in these complex ferrimagnetic alloys.
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Metallic conduction and large electron phonon impurity interference effect in single TiSi nanowires

Metallic conduction and large electron phonon impurity interference effect in single TiSi nanowires

We report on the first electrical characterizations of single-crystalline TiSi nanowires (NWs) synthesized by chemical vapor deposition reactions. By utilizing the focused-ion-beam-induced deposition technique, we have delicately made four-probe contacts onto individual NWs. The NW resistivities have been measured between 2 and 300 K, which reveal overall metallic conduction with small residual resistivity ratios in the NWs. Surprisingly, we find that the effect due to the interference processes between the elastic electron scattering and the electron-phonon scattering largely dominates over the usual Boltzmann transport even at room temperature. Such prominent electron-phonon-impurity interference effect is ascribed to the presence of large amounts of disorder and high Debye temperatures in TiSi NWs.
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Studies of Phonon Anharmonicity in Solids

Studies of Phonon Anharmonicity in Solids

each nucleus onto a classical system of several fictitious particles governed by an effective Hamiltonian, derived from a Feynman path integral, for example. [32, 33] Such low temperature quantum effects are beyond the scope of this work. Nev- ertheless, our results should not be altered significantly by quantum effects for the following reasons. Our particular interest is in anharmonic phonon-phonon interactions at higher temperatures, and our new results concern the phonons and NTE above 250 K. A classical MD simulation is usually appropriate at higher tem- peratures. The modes most subject to quantum corrections are those involving the dynamics of the lower mass O atoms, but these are at high energies. They are not activated at 40 K, and show weak anharmonic effects. Relatively larger anhar- monic effects at low temperatures are found in the modes below 10 meV. These are dominated by the Ag atoms, but with their high mass only tiny quantum effects are expected. There are several semi-quantitative methods to estimate the magnitudes of quantum corrections. For example, Berens, et al. [140] and Lin, et al. [44] suggest that quantum effects could be evaluated from the difference between the quantum and classical vibrational energy or free energy derived from the corresponding par- tition functions. These methods do not account for all quantum effects on nuclear trajectories, but for Ag 2 O at 40 K, by using both classical and quantum paritition
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Anharmonic phonon decay in cubic GaN

Anharmonic phonon decay in cubic GaN

temperatures. However, the central values show a regular trend that follows closely the solid line calculated by using the occupation factors appearing in Eqs. (2) and (3). This fact leads us to think that the anharmonic lifetime values determined from the Raman measurements are fairly accurate even at lower temperatures. We obtain 4.2 and 2.0 ps at low temperature and room temperature, respectively. These values are in excellent agreement with the values theo- retically predicted by Barman and Srivastava. 8 The room-temperature LO phonon lifetime we find for c-GaN is higher than the values around 0.9 ps reported for the A 1 (LO) mode of wurtzite GaN. 18,34 The values of the anharmonic lifetimes are relevant for the buildup of a nonther- mal phonon population and therefore for determining the hot-carrier relaxation dynamics by electron-phonon interaction. Given the relatively high values of anharmonic phonon lifetimes in c-GaN, hot-phonon effects may be expected to be significant in this material.
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Relaxation of Energy and Momentum in an Carrier Phonon System

Relaxation of Energy and Momentum in an Carrier Phonon System

On the other hand, as pointed out in ref. [2], fractal or power law distribution functions are of interest in solid state Physics. An example, given in ref. [2], is the ther- malization, due to the electron-phonon interactions, of a non-equilibrium electron-phonon system which occurs if electrons and holes in metals or semiconductors are heated to a temperature T e greater than the lattice tem-

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Comparison of Theoretical Models of Electron Phonon Coupling in Thin Gold Films Irradiated by Femtosecond Pulse Lasers

Comparison of Theoretical Models of Electron Phonon Coupling in Thin Gold Films Irradiated by Femtosecond Pulse Lasers

This study reports on a comparison of theoretical models for electron-phonon coupling that is substantially associated with non- equilibrium energy transport in thin gold films irradiated by femtosecond pulse lasers. Three published electron-phonon coupling models were analyzed with the use of a well-established two-temperature model to describe non-equilibrium energy transport between electrons and phonons. Based on the numerical results, at lower fluence, all models showed nearly similar tendencies, whereas at higher fluence, constant electron- phonon coupling forced unrealistically long electron-phonon equilibration times and spatially long diffusive regions as it failed to intrinsically consider the effect of a high number density of excited d-band electrons. Even at higher fluence, however, both Lin’s and Chen’s models yielded physically reasonable results, showing converging electron-phonon equilibration times and steep gradients in the spatial lattice temperature profiles at higher laser fluence. In particular, Lin’s model predicts nonlinear characteristics of heat capacity and lattice temperature with respect to laser fluence better than Chen’s model. Moreover, the electron-phonon relaxation time increased with laser fluence, whereas at laser fluence greater than 0.05 J/cm 2 , the thermal equilibrium time was nearly independent of the laser fluence. Thus, it was concluded that Lin’s model better
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Tailoring the nature and strength of electron phonon interactions in the SrTiO3(001) 2D electron liquid

Tailoring the nature and strength of electron phonon interactions in the SrTiO3(001) 2D electron liquid

nature. This is illustrated in Fig. 2 f,l. In this regime, the quasiparticle dispersion shows a weak kink at an energy of ≈ 30 meV and no signs of replica bands can be discerned in the raw data or in curvature plots (see Supplementary Information, Fig. S4), providing direct evidence for a suppression of the long-range Fr¨ ohlich interaction. Instead, consistent with Ref. [7], we find that the spectral function and e-p self-energy of the high-density 2DEL can be described by Migdal-Eliashberg theory with λ ≈ 0.7 and the same coupling to the entire phonon density of states.

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Phonon Precursors to the High Temperature Martensitic Transformation in Ti50Pd42Cr8

Phonon Precursors to the High Temperature Martensitic Transformation in Ti50Pd42Cr8

various transition metals the transformation temperatures decreases and various intermediate incommensurate phases and different types of Martensites appear. The most extensive study of the phase diagram was by Mateeva[5] and reported by Enami [6]. Most of the work focused on the structure of the Martensitic phase, However a detailed study of TiPd-Cr investigated the modulated cubic structure that appears upon cooling by means of electron diffraction (ED) and high resolution transmission electron microscopy (HRTEM) for various Cr substitution [7].

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Phonon-phonon interactions and phonon damping in carbon nanotubes

Phonon-phonon interactions and phonon damping in carbon nanotubes

We shall consider two important mechanisms for the decay of long-wavelength acoustic phonons in single-wall CNTs, namely electron-phonon (e-ph) and ph-ph scatter- ing. We show that the dominant e-ph coupling terms (re- sulting from the deformation potential contribution) do not allow for phonon decay due to kinematic restrictions, and thus an intrinsic upper bound for the temperature- dependent quality factor of the various modes can be derived from ph-ph interactions alone. These upper bounds are given below. The problem of phonon de- cay has in fact a rather long history. Early work on the decay of an optical phonon into two acoustic phonons via anharmonicities 45,46 proposed a scheme for nonlin- ear phonon generation. Phonon decay via ph-ph inter- action is also important for the understanding of neu- tron scattering data 40 and for the collective excitations
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Raman study of phonon modes in bismuth pyrochlores

Raman study of phonon modes in bismuth pyrochlores

For BZN, no physical process has been suggested to be re- sponsible for the high amplitude of this mode. Normally, a two phonon-scattering process is expected to have a much lower probability than a first-order process. Physical pro- cesses such as resonant raman scattering, where the incident laser frequency is close to a resonance in the material, can greatly increase the amplitude of an overtone or combination band. Strong anharmonic coupling can also lead to the ap- pearance of combination and overtone bands. 43 There is no

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