Microscopic theory of the long-wavelength modes of two-component plasmas and ionic liquids: II. The longitudinal modes

The modification of the damping rate of the sound modes by Coulomb phenomena is demonstrated from first principles. The heat modes of one- and two-component systems of charged particles are shown to differ by a factor c_p/c_v. Microscopic expressions for the interspecies energy and longitudinal momentum relaxation frequencies are provided. The charge relaxation modes are shown to reduce in the limit of weak-coupling to a pair of plasma oscillations occurring slightly below the plasma frequency while being slightly damped even at infinite wavelength. In the opposite limit of strong-coupling the same pair of charge relaxation modes is shown to split into an interspecies momentum relaxation mode and an approximate hydrodynamic diffusion mode. An Einstein relation between the diffusion constant and the electric conductivity is also demonstrated. All expressions are obtained for arbitrary density and coupling.     

Impedance and modulus spectroscopy of “real” dispersive conductors

Power law dispersions in the bulk, intragranular, ac conductivity and permittivity of a non-ideal solid electrolyte are modelled by a frequency-dependent admittance in parallel with the R, C elements of a conventional equivalent circuit. Expressions are derived for imaginary parts of the complex impedance Z″ and electric modulus M″ for such a dispersive conductor. The dependance of the shapes of the Z″ and M″ versus frequency peaks on the equivalent-circuit parameters are illustrated. Z″ and M″ are predicted to peak at different frequencies. An analysis of Na β-alumina data is presented. It is shown that the hopping rate of ions in a solid electrolyte can be obtained from the functional form of Z″ and M″ peaks and the frequency separation of their peak maxima.     

Evidence for a new phase transition in Rb2ZnCl4 by Raman scattering

The Raman spectra of an oriented single crystal of Rb₂ZnCl₄ give evidence for the existence of a phse mode at low temperature, as predicted by Wada et al. A new soft mode whose frequency decreases as the temperature T₃?72 K is approached from below, was observed in the a(cc)b scattering orientation, strongly supporting the onset of a new phase transition.     

Optical conductivity of a two-band superconductor

Within the two-band superconductor model, which is a generalization of the standard BCS model to the case of a complicated crystal structure, an expression has been obtained for the conductivity of the superconductor at an arbitrary frequency of the external electromagnetic field. This expression has been derived using the microscopic theory in the framework of the diagram technique for nonequilibrium processes. The σ(ω) dependencies calculated for T = 0 are compared with the results of single-band models with the s and d symmetries of the order parameter. It has been shown that the behavior of the optical conductivity as a function of the frequency depends strongly on the doping level.     

Free vibration of a spherical liquid drop attached to a conical base in zero gravity

Free vibration analysis of a spherical liquid drop attached to a conical base is presented. Assuming the liquid is incompressible and inviscid, and introducing a velocity potential, axisymmetric and asymmetric vibration characteristics are clarified, considering two liquid contact conditions: slipping edge and anchored edge. In the numerical calculations, for a wide range of conical base apex angles, the natural frequency and vibration mode of a liquid drop are presented. From these parameters, the vibration characteristics of a liquid drop attached to a conical base with general apex angle can be easily predicted. When the apex angle tends to 180°, natural frequencies are found to converge to those of a spherical drop under both slipping and anchored edge conditions, except in the axisymmetric mode with meridian mode number m=0 in the anchored edge case and asymmetric mode m=1 and n=1 in the slipping edge case.     

The influence of the skin effect on FMR in MnFe ferrites

FMR experiments on the system Mn _x Fe_3?x O₄ have been performed at 7·8 and 15·2 (or 16) GHz in the temperature range 80–300 K. The temperature dependences of the linewidth, resonance field and lineshape have been studied on spherical samples with diameter 0·25–1 mm. It has been shown that the observed dependences from greater part reflect the decrease of the skin depth with increasing temperature and are connected with the influence of the skin effect. This mechanism is discussed in more detail. The maxima in theΔH vs.T plot are compared to similar ones predicted for an infinite slab. The behaviour of the resonance field and lineshape is shown to be essentially dependent on the position of the uniform mode frequency to the upper limit of the spin-wave manifold. An approximative method has been given for treating resonance in the surface layer of the spherical sample and the corresponding surface mode. This mode and a further mode similar to the Walker magnetostatical (3,1,1) mode have been observed at higher temperatures. It has been experimentally verified that they can coexist with the nearly uniform mode.     

Electrical properties of silver-intercalated hafnium disulfide in DC and AC electric fields

The temperature dependences of the direct-current (dc) and alternating-current (ac) resistivities of silver intercalated compounds Ag _x HfS ₂ have been measured using impedance spectroscopy over a wide frequency range at different temperatures for the first time. The dc conductivity has an activation behavior and increases with increasing silver content in the samples. The results of the ac measurements have demonstrated that the ac conductivity has a frequency dispersion described by “the universal dynamic response.” It has been shown that the relaxation processes in an ac field are accelerated when the silver content in the sample and temperature increase.     

Acoustic relaxation and internal strains in KCl:CN

Data revealing a previously predicted relaxation peak in the propagation of T_2g mode ultrasound in KCl doped with 15–140 ppm KCN is presented and analyzed. A distribution of activation energies is found; the mean value is identified with a thermal conductivity resonance, and the width of the distribution is taken to confirm Pompi's assumption of internal strains in his analysis of specific heats and electric field dichroism in KCl:CN. The interaction of internal strains with the rotational components of the measuring shear wave suggests new sources for the observed acoustic effects in KCl:CN.     

The influence of phonons on the optical properties and the conductivity of quasi-one-dimensional metals

The frequency dependent conductivity σ(ω) completely taking into account the interaction between electrons is studied. The shape and the temperature dependence of optical absorption near the frequency of a molecular phonon activated due to the interaction with electrons are found. For a system with attractive sign of the e-e backward scattering amplitude g₁<0 an absorption edge near the gap 2Δ in the electronic spectrum is studied. A low frequency conductivity is discussed. The properties under consideration depend essentially on the magnitudes of e-e interactions and are critical to the sign of g₁.     

Electrical conductivity of a fully ionized plasma at high frequencies

When the frequency of the electric field is of the order of, or larger than, the electron plasma frequency, kinetic equations are no longer valid. The Klimontovich equation linearized in the applied electric field is solved systematically by means of an expansion into powers of the square root of the plasma parameter. A general expression up to second order is obtained for the conductivity σ(ω, k). There exists a large overlap with the results of an earlier paper on the conductivity at low frequencies. This overlap is used to determine a cut-off parameter. The expression for the conductivity serves as a basis for the calculation of the influence of collisions on the dispersion relation for plasma waves. It appears that for small wavenumbers the influence of electron-ion collisions is dominant compared to electron-electron collisions.     

The rotation-vibration spectrum and double-minimum ν12 potential function of propadienone: A semirigid bender analysis

Propadienone is an interconverting molecule having a pair of equivalent symmetry related conformers separated by an energy barrier rising well above the vibrational ground state. Microwave spectra of molecules in excited states of the large-amplitude in-plane bending mode ν₁₂, including intersystem lines, have been successfully represented using the semirigid bender model. The model reveals a double-minimum bending potential with a barrier rising 359 cm⁻¹ above the minima at C₁C₂C₃ = 142°. In the ground state the interconversion frequency is 3.7 GHz and the ν₁₂ fundamental frequency is predicted to be 160 cm⁻¹. Analysis of other vibrational satellites involving the lowest-frequency out-of-plane mode ν₈ indicates a vibrational frequency of 240 cm⁻¹. The inplane vibrational satellite and also the ground state substitution spectra are quite accurately reproduced by the model. Our generalized semirigid bender method offers a variety of approaches to fitting molecular parameters to the experimental data.     

Dielectric relaxation spectroscopy of phlogopite mica

An in-depth investigation of the dielectric characteristics of annealed phlogopite mica has been conducted in the frequency range 0.1 Hz–10 MHz and over the temperature range 653–873 K through the framework of dielectric permittivity, electric modulus and conductivity formalisms. These formalisms show qualitative similarities in relaxation processes. The frequency dependence of the M″ and dc conductivity is found to obey an Arrhenius law and the activation energy of the phlogopite mica calculated both from dc conductivity and the modulus spectrum is similar, indicating that same type of charge carriers are involved in the relaxation phenomena. The electric modulus and conductivity data have been fitted with the Havriliak–Negami function. Scaling of M′, M″, ac conductivity has also been performed in order to obtain insight into the relaxation mechanisms. The scaling behaviour indicates that the relaxation describes the same mechanism at different temperatures. The relaxation mechanism was also examined using the Cole–Cole approach. The study elaborates that the investigation regarding the temperature and frequency dependence of dielectric relaxation in the phlogopite mica will be helpful for various cutting edge applications of this material in electrical engineering.     

Light scattering from E-symmetry amplitudon in the incommensurate phase of quartz

Low frequency depolarized Raman spectra of quartz were investigated in the incommensurate phase near the α-β transition at T_c = 573°C. A weak mode, but underdamped in the temperature region close to the commensurate α phase, was observed at about 8 cm^-1 with an intensity proportional to the square of the order parameter. The mode is assigned as the E-symmetry amplitudon which has been predicted to exist in the “3-k state” of the incommensurate phase, in addition to a totally symmetric A-amplitudon.     

Optical conductivity of single walled nanotube films in the Terahertz region

A theoretical investigation for the conductivity of single walled nanotube films is carried out with an effective medium model in the Terahertz region. The results are compared with the recent experiment and a decrease of the real conductivity with increasing frequency is predicted. Meanwhile, the off-diagonal components of the dielectric function of single-walled carbon nanotube films based on the magnetooptical effects are also shown.     

Transient processes in two-barrier nanostructures

An analytic solution to the problem on transient processes in a two-barrier nanostructure is found. Explicit expressions are obtained for a transient current produced by an instantly applied weak electric field. The current relaxes to a stationary state for a time ?/Γ (Γ is the width of a resonance level), oscillating at a frequency of ξ = ? ? ? _R , where ? is the energy of electrons coming from an emitter and ? _R is the resonance level energy. The transient current for interacting electrons is found in the quasi-classical approximation. It is shown that interaction between electrons can drastically change the transient current, especially in the presence of hysteresis of the current-voltage characteristic (CVC). Near extreme CVC values in the region of negative differential conductivity, the oscillation frequency tends to zero and becomes imaginary, compensating the decay. Thus, the transient current relaxes with very large times without oscillations. In contrast, in the case of positive differential conductivity, the oscillation frequency becomes very high, while the relaxation time remains the same, 1/Γ.     

Calculations of three-dimensional magnetic excitations in permalloy nanostructures with vortex state

Dynamic susceptibility spectra of the vortex state in nanorings and nanodots are studied using three-dimensional micromagnetic simulations. Spatial maps of the susceptibility have enabled identification of various resonance modes. For an exciting field along the x axis, several resonance peaks appear for a thin dot, including a core mode, whereas only one main resonance peak is detected for a ring corresponding to a volume mode with uniform magnetization perpendicular to the exciting field (x direction). A low-frequency resonance peak related to a surface mode and a high-frequency resonance peak viewed as an edge mode are additionally observed for a thick ring. These three resonance modes (surface, volume and edge modes) which correspond to low, intermediate and high-frequency resonance peaks, respectively, are also captured for an exciting field along the y axis. In addition, a mixed edge and volume mode is revealed at a higher frequency.     

Low-frequency crossover of the fractional power-Law conductivity in SrRuO3

We combine the results of terahertz time-domain spectroscopy with far-infrared transmission and reflectivity to obtain the conductivity of SrRuO3 over an unprecedented continuous range in frequency, allowing us to characterize the approach to zero frequency as a function of temperature. We show that the conductivity follows a simple phenomenological form, with an analytic structure fundamentally different from that predicted by the standard theory of metals.     

ac Conductivity of semiconducting trans-polyacetylene

The ac conductivity of semiconducting trans-polyacetylene has been measured over the frequency range 10 Hz to 10 MHz at room temperature. Both ohmic and blocking contacts were used on samples prepared at several doping levels below the metallic limit. The complex conductivity was found to be frequency independent for all levels of doping and for both types of contacts. A discussion is given regarding soliton motion and inhomogeneous doping and their possible effects on ac conductivity in trans-polyacetylene.     

Electrophysical response of thin-film titanium-containing nanocomposites based poly(<Emphasis Type="Italic">p</Emphasis>-xylylene) on change of the atmosphere

The dependence of the conductivity of poly(p-xylylene)-based titanium-containing nanocomposites on the extent of adsorption of polar molecules from the atmosphere is observed, while nonpolar molecules induce no such changes. A relationship between the dipole moment of the adsorbate molecule and the sensitivity of the composite conductivity to its vapor is revealed. A composite with filler content near the percolation threshold shows the highest sensitivity to polar gases. A model is proposed to explain the change in the resistance upon vapor adsorption by the formation of a surface dipole. Since the investigated vapors are adsorbed as donors, their adsorption reduces the electron work function of the nanoparticles, thereby increasing the conductivity. The dielectric spectrum of a nanocomposite containing 2 vol % titanium dioxide is very closely approximated by the Cole–Cole and Maxwell–Wagner equations, whereas the frequency dependence of the electric modulus is close to that predicted by the Debye law.     

What is the highest T c for phonon-mediated superconductivity?

We suggest that the high-temperature superconductivity can be attributed to the director-roles of the van Hove singularity between an electron-electron interaction and an electron-phonon interaction. The difference between the critical temperature and the pairing temperature is presented, and the Fermi arc, the d-wave symmetry and the poor conductivity, etc., are discussed. In particular, the non-s-wave symmetry is predicted to have the highest T _c for superconductors.