Phonon Research Papers - Academia.edu (original) (raw)

The temperature and composition dependence of the electrical conductivity of cadmium vanadate semiconducting glasses formed with V2O5 as a unique network former has been studied in this paper. The results for these glasses have been... more

The temperature and composition dependence of the electrical conductivity of cadmium vanadate semiconducting glasses formed with V2O5 as a unique network former has been studied in this paper. The results for these glasses have been compared with those for traditional vanadate glasses formed with different traditional network formers (phosphate, borate, etc). The variation of the conductivity and the activation energy with composition for the cadmium vanadate glasses is much stronger than that for the traditional vanadate glasses. The strong compositional variation of the conductivity and the activation energy for the present glasses has been attributed to the significant structural changes observed in the Fourier transform infrared (FT-IR) spectra due to the introduction of a CdO modifier in the glassy matrix. The experimental results have been analysed in the light of the existing theories of polaronic conduction. It has been observed that the electrical conduction at high temperatures in these glass compositions is described by Mott's phonon-assisted hopping model, while the low-temperature data in a limited temperature range are consistent with the variable-range hopping model. The parameters obtained from the fits of these models to the experimental data are reasonable.

We present an overview of the recent progress made in the development of a far-IR array of ultrasensitive hot-electron nanobolometers (nano-HEB) made from thin titanium (Ti) films. We studied electrical noise, signal and noise bandwidth,... more

We present an overview of the recent progress made in the development of a far-IR array of ultrasensitive hot-electron nanobolometers (nano-HEB) made from thin titanium (Ti) films. We studied electrical noise, signal and noise bandwidth, single-photon detection, optical noise equivalent power (NEP), and a microwave SQUID (MSQUID) based frequency domain multiplexing (FDM) scheme. The obtained results demonstrate the very low

of the PhD Thesis "long-wavelength magnons and phonons and rotonlike excitations in amorphous solids" by Dipl.-Phys. Rolf Ottking from Minden (Westf.) Extended inhomogeneities and variations of the nearest-neighbour distances... more

of the PhD Thesis "long-wavelength magnons and phonons and rotonlike excitations in amorphous solids" by Dipl.-Phys. Rolf Ottking from Minden (Westf.) Extended inhomogeneities and variations of the nearest-neighbour distances are a characteristic common property of amorphous solids. Essential information about the (magnetic) structure of amorphous solids can be yielded from the static structure factor and the radial distribution function, resp. The inhomogeneities lead to damping and renormalization of the sound velocity and the stiffness constant of long- wavelength magnons and phonons. Magnons and phonons with very large wavelength are scattered from the inhomogeneities acting as point defects and one gets magnon- and phonon- Rayleigh scattering, resp. The results mentioned follow as well from a Green’s function theory (Matsubara-Kaneyoshi formalism) as - for magnons- from quantum mechanical perturbation calculations. For magnons and phonons with wavelengths shorter than...

Transition Edge Sensor (TES) quantum microcalorimeters can provide intrinsic arrival time and energy resolved measurements of individual photons over a large energy range centered on the optical band. Our TESs consist of thin-film... more

Transition Edge Sensor (TES) quantum microcalorimeters can provide intrinsic arrival time and energy resolved measurements of individual photons over a large energy range centered on the optical band. Our TESs consist of thin-film superconduting tungsten pixels on a silicon substrate. The pixels are voltage-biased to remain in the sharp superconducting transition region through negative electrothermal feedback. We report progress on our first imaging TES array of 32 pixels. We describe the experimental apparatus, summarize recent progress, characterize detector performance and outline the future path of TES development.

The pillared-graphene architecture is a conceivable way of conjoining graphene nanoribbons and carbon nanotubes (CNT) in nanoelectronics. Especially promising is its capability to dissipate thermal energy in thermal management... more

The pillared-graphene architecture is a conceivable way of conjoining graphene nanoribbons and carbon nanotubes (CNT) in nanoelectronics. Especially promising is its capability to dissipate thermal energy in thermal management applications. However the thermal boundary resistance (Kapitza resistance) at the graphene nanoribbon-CNT interface is a phonon barricade and the bottleneck to efficacious heat extraction. Parallel to strain studies on thermal conductance, this work is a first report on the effects of mechanical strain on the interfacial phonon dynamics in the pillared-graphene nanostructure (PGN). Molecular dynamics simulations are employed to derive the changes in phononics as axial, torsional, and compound strain of various degrees are applied on PGN. The pillar lattice structure behaves dissimilarly to the different types of strains. iTO mode softening as induced by torsional strain is more effective than LO softening (triggered by tension) in minimizing the thermal boundary resistance. Essentially, it is shown that there is a strong relationship between strained PGN pillar lattice structure, interfacial phononics, and thermal boundary resistance.

The optical reflectivity of Pb_0.865Sn_0.135Se and Pb_0.75Sn_0.25Se solid solutions was measured in the THz spectral region energetically corresponding to bulk optical phonon excitations and in the temperature range from 40 K to 280 K.... more

The optical reflectivity of Pb_0.865Sn_0.135Se and Pb_0.75Sn_0.25Se solid solutions was measured in the THz spectral region energetically corresponding to bulk optical phonon excitations and in the temperature range from 40 K to 280 K. The analysis of Pb_0.75Sn_0.25Se data performed within the dynamic dielectric function formalism revealed a new effect due to the electron-phonon coupling resulting in resonant changes of LO phonon frequency for energy gap equal to zero or to LO phonon energy. This effect is absent for Pb_0.865Sn_0.135Se that exhibits an open energy gap with trivial band ordering at all temperatures. These results show that reflectivity in the THz range constitute a versatile experimental method for precise determination of band inversion in narrow-gap topological materials. For Pb_0.75Sn_0.25Se the transition from trivial insulator to topological crystalline insulator phase takes place at temperature T_0 = (172 ± 2) K.

Stationary straight cracks in quasicrystals in linear elastic setting are under scrutiny. The analysis is developed by using Stroh formalism which is modified to account for a totally degenerate eigenvalue problem: in fact, the... more

Stationary straight cracks in quasicrystals in linear elastic setting are under scrutiny. The analysis is developed by using Stroh formalism which is modified to account for a totally degenerate eigenvalue problem: in fact, the fundamental matrix of the governing equations of motion admits a repeated eigenvalue corresponding to a single eigenvector. Cases of a semi-infinite rectilinear crack loaded along its margins and a crack of finite length under remote loading conditions are considered. Standard and phason stresses display square-root singularities at crack tip. The latter stresses represent peculiar microstructural inner actions occurring in quasicrystals and are determined by rearrangements assuring quasi-periodicity of the atomic tiling—modes described by a vector field, called phason field, collecting the local degrees of freedom exploited by the atoms within the material elements. Energy release rate increases with the coupling parameter between displacement and phason fields.

To study the emission properties of an AlGaAs–GaAs phonon laser we develop a formalism similar to that used to describe a laser. The device studied here consist of a double-barrier resonant tunneling diode tailored to generate an intense... more

To study the emission properties of an AlGaAs–GaAs phonon laser we develop a formalism similar to that used to describe a laser. The device studied here consist of a double-barrier resonant tunneling diode tailored to generate an intense rate of primary LO1 phonons. These phonons are confined in the well and they decay into a pair of secondary LO2 and TA phonons. The TA phonons are generated by stimulated emission and they are partially reflected in the well walls. A combination of these two processes leads, for injection rates greater than the threshold, to the selection of a single phonon mode. Finally, the TA phonons escape through the barriers forming an intense coherent phonon beam. We start with a Hamiltonian that takes into account the electrons, the three phonon branches, the electron–phonon interaction and the phonon–phonon interaction. The last one is responsible for the TA phonon generation. From this Hamiltonian we get a set of five coupled Heisenberg–Langevin equations that are solved making an expansion in coherent states and doing the usual adiabatic approximation. The threshold for phonon lasing is calculated. The results show that it is not necessary to have a big pumping to get a single mode operation. This confirm our previous results obtained using rougher approximations. The phonon laser studied here has a very short wavelength. The mean free path of TA phonons is of the order of 2 mm. Therefore, it could be useful to perform acoustic nanoscopy and other applications.

Effects of the electron-phonon interaction in carbon-based materials can be seen in many physical properties, ranging from relatively high-Tc superconductivity in doped fullerenes and graphite intercalated compounds to being a limiting... more

Effects of the electron-phonon interaction in carbon-based materials can be seen in many physical properties, ranging from relatively high-Tc superconductivity in doped fullerenes and graphite intercalated compounds to being a limiting factor on the mobility of carriers in carbon ...

We studied spatially isolated single-walled carbon nanotubes (SWNTs) immobilized in a quasi-planar optical λ/2-microresonator using confocal microscopy and spectroscopy. The modified photonic mode density within the resonator is used to... more

We studied spatially isolated single-walled carbon nanotubes (SWNTs) immobilized in a quasi-planar optical λ/2-microresonator using confocal microscopy and spectroscopy. The modified photonic mode density within the resonator is used to selectively enhance or ...