Electrodynamic Response Research Articles

Electrodynamic response of metal spheres

A collective dipole model for the electrodynamic response of small metal spheres is presented. Model calculations of the extinction and scattering cross sections of metal spheres as a function of particle radius are compared with the exact Mie formulas. The characteristic size dependences of the peak position, width, and height of the dipole surface plasmon in small metal particles are attributed to the collective nature of the motion.

Flux-line-cutting and flux-pinning losses in type-II superconductors in rotating magnetic fields

A general critical-state theory, including the effects of both flux-line cutting and flux pinning, is proposed for calculations of hysteresis in type-II superconductors in parallel applied magnetic fields that vary in both magnitude and direction. In this theory, if the magnitude of the electrical-current-density component perpendicular to the magnetic induction $\stackrel{\ensuremath{\rightarrow}}{\mathrm{B}}$ exceeds the corresponding critical value ${J}_{c\ensuremath{\perp}}$, depinning occurs, and an electric field component ${E}_{\ensuremath{\perp}}$ perpendicular to $\stackrel{\ensuremath{\rightarrow}}{\mathrm{B}}$ appears; if the magnitude of the current-density component parallel to $\stackrel{\ensuremath{\rightarrow}}{\mathrm{B}}$ exceeds the corresponding critical value ${J}_{c\ensuremath{\parallel}}$, flux-line cutting occurs, and an electric field component ${E}_{\ensuremath{\parallel}}$ parallel to $\stackrel{\ensuremath{\rightarrow}}{\mathrm{B}}$ appears. Model calculations are performed to solve for the electrodynamic response of a slab subjected to a parallel, constant magnetic field whose direction undergoes either continuous rotation or periodic oscillation. The relation of the theory to the pioneering experiments of LeBlanc and co-workers is discussed.

Electrodynamic response of a bounded electron gas in hydrodynamic formalism: Theory and applications

Coupled integral equations for the electrodynamic response of a bounded electron gas are written down within a unified hydrodynamical model. The nonretarded limit of the formalism is considered in detail and the induced density fluctuation is expressed in terms of the external potential. Within this formalism a simple proof is produced of the known theorem that the long-wavelength surface-plasmon frequency of such a system is independent of either the surface-electron density profile or the hydrodynamic dispersion effect. The theory is applied to the problem of interaction of a moving external point charge with a jellium metal surface. The surface-electron density profile is treated in one- and two-step models. Hydrodynamic dispersion effects as well as the effects of the surface diffuseness and of the finite electron velocity of the external charge on the dynamical image-charge interaction are discussed. The relevance of some of these theoretical results to certain experimental situations involving the interaction of a metal surface with electrodynamic probes is pointed out.

Response functions and the retarded surface plasmon for bounded jellium

Abstract The self-consistent retarded electrodynamic response of bounded jellium is analyzed for independent electrons in the infinite barrier model. Within the RPA, and for q ⪡ kF, a set of coupled integral equations is developed which can be solved for the response functions of the system. The retarded surface plasmon dispersion emerges immediately from this formalism.

Investigation of the far-infrared properties of superconducting mercury films

Measurements are presented on the far-infrared properties of superconducting films. On the basis of a careful analysis of the electrodynamic properties of a two layer system (film and substrate), the electrodynamic response function σ = σ 1 − iσ 2 of superconducting mercury is determined from simultaneous absorption and transmission measurements. It can be concluded that strong-coupling effects are important; they manifest themselves in deviations of σ 2 from the usual weak-coupling BCS-behaviour. Clear evidence is given that the absorption (or equivalently σ 1) is equal to zero below the gap frequency, contrary to results found earlier. From the measurements it is concluded that freshly evaporated mercury condenses first as a non-conducting layer and then in the form of β-mercury. The energy gap of β-mercury is measured to be v ̃ g = (14.5 ± 0.2) cm -1 leading to a parameter h ̵ omega; g/kT c = 5.3 which is higher than the value of most other known superconductors.

Far-infrared and superconductivity

A review of the electrodynamics of superconductors is presented, neglecting questions related to the Josephson-effect. Following a historical introduction, the experimental techniques are sketched. A more detailed analysis of the high-frequency electrodynamics of metals is given, and the influence of temperature, strong-coupling effects, paramagnetic impurities, magnetic fields and proximity-effects on the electrodynamic response of superconductors is discussed.

On the interdependence of van der waals and double layer forces

We study the effect of coupling the electrostatic and low frequency electrodynamic responses of colloidal systems. Exact results are reported for the van der Waals free energy of interaction of non-uniform electrolyte across planar dielectric and planar charged dielectric across non-uniform electrolyte. In both cases, the results depend on the double layer repulsion.

Electron Spin Waves in Nonmagnetic Conductors: Self-Consistent-Field Theory

A general derivation of the electrodynamic response of a quantum many-electron gas in a nonmagnetic conducting solid immersed in an applied magnetic field is given. Self-consistent-field (SCF) theory of the equation of motion of the one-electron density matrix is used in such a way as to include, from the outset, one-electron effects such as complex energy band structure, spin-orbit coupling, and spin paramagnetism. This treatment specifically omits exchange effects such as those encountered in an extended random-phase approximation or Landau-Fermi liquid theory. The aim is to study the properties of wave propagation in the gas, looking for spin waves and/or characteristic effects which uniquely involve the spin degree of freedom and the paramagnetism of the equilibrium state. The derived results contain terms which have been neglected previously and terms which do not evolve from a simple generalization of previous treatments of the quantum dielectric theory of a Fermi gas. There are interesting spin effects in the plasma wave properties both with and without spin-orbit mixing of the one-electron states. In an effective mass approximation for the one-electron states, it is shown that there are resonances and cutoffs associated with electron spin resonance in the transverse wave propagation (both perpendicular and parallel to the magnetic field). For spin-orbit mixed states, one finds zeros of the longitudinal dielectric constant (for long wavelength) near the electron spin-flip frequency. The mechanism for the spin wave associated with this zero is a correlation of the motion of electrons with "opposite spins" by the long-range Coulomb field through the spin-orbit coupling of the crystalline eigenstates.

Time-dependent Ginsburg-Landau theory

The results of a microscopic-theory calculation of the electrodynamic response of a local superconductor to slowly varying fields, are presented.

Inductive MHD Generator

The electrodynamic response of a particular inductive magnetohydrodynamic generator is calculated. Expressions for the output voltage and output power are derived. The results of experiments conducted with the generator mounted on an electromagnetic shock-tube agree with the theoretical predictions. The measured output power is of the order of 10 watts lasting for a few microseconds.