Scintillation Arc Brightness and Electron Density for an Analytical Noodle Model

We show that narrow filaments or sheets of over- or under-dense plasma, or “noodles,” with fluctuations of scattering phase of less than a radian, can form the scintillation arcs seen for many pulsars. The required local fluctuations of electron density are indefinitely small. We assume a cosine profile for the electron column and find the scattered field by analytic Kirchhoff integration. For a large electron column, corresponding to large amplitude of phase variation, the stationary-phase approximation is accurate; we call this regime “ray optics”. For smaller-amplitude phase variation, the stationary-phase approximation is inaccurate or inapplicable; we call this regime “wave optics”. We show that scattering is most efficient when the width of the strip equals that of one pair of Fresnel zones, and in the wave-optics regime. We show that the resolution of present observations is about 100 Fresnel zones on the scattering screen. Incoherent superposition of strips within a resolution element tends to increase the scattered field. We find that observations match a single noodle per resolution element with phase of up to 12 radians; or many noodles per resolution element with arbitrarily small phase variation each, for net phase of less than a radian. Observations suggest a minimum radius for noodles of about 650 km, comparable to the ion inertial scale or the ion cyclotron radius in the scattering plasma.

MAGNETOPOLARON IN A CYLINDRICAL QUANTUM DOT

We examine the magnetopolaron state in a cylindrical quantum dot with a transverse parabolic potential and a high rectangular potential well in the longitudinal direction. The quadratic dependence of the magnetopolaron energy versus Fröhlich electron–phonon coupling constant for different cyclotron radii and constant structure radius is modulated by a logarithmic function seems to depend on the Fröhlich coupling constant. The same law is seen in the case of magnetopolaron energy versus Fröhlich electron–phonon coupling constant for different structure radii and constant cyclotron radius. The energies are seen to be lifted in different fashions in the case of the structure and cyclotron radii. The high degrees of confinement (or high magnetic field) lead to an enhancement in the effective electron–phonon coupling that in turn brings about the possibility that in spite of weak polar coupling as in GaAS say, the polaron problem may also have strong-coupling counterparts arising from confinement or magnetic field effects. The polaron mass increases with increasing Fröhlich electron–phonon coupling constant. The dependence seems to be fourth-order law of the Fröhlich coupling constant modulated by a logarithmic function.

Ultra-cold plasmas: a paradigm for strongly coupled and classical electron fluids

Ultra-cold plasmas obtained by ionization of atomic Rydberg states are qualified as classical and strongly coupled electron fluids. They are shown to share several common trends with ultra-cold electron flows used for ion-beam cooling. They exhibit specific stopping behaviour to charged particle beams, which may be used for diagnostic purposes. Ultra-cold plasmas are easily strongly magnetized. Then, one expects a strongly anisotropic behaviour of low ion velocity slowing down when the target electron cyclotron radius becomes smaller than the corresponding Debye length.

Magnetocapacitance Investigation of Quantum Hall Effect and Edge States

The quantum Hall effect for the GaAs/AlGaAs heterostrcture is investigated by an ac capacitance measurement between the two-dimensional electron system (2DES) and the gate on GaAs/AlGaAs. The capacitance minima at the quantum Hall plateaus are mainly determined not by the 2DES area under the gate but by the edge length of 2DES. There exists the high conductive region due to the edge states along the 2DES boundary, when the bulk conductivity σxx is small enough at low temperatures and high magnetic fields. From the temperature and frequency dependence of the capacitance minima, it is found that the measured capacitance consists of the contribution from the edge states and that of the bulk state, which is treated as a distributed circuit of a resistive plate with the conductivity σxx. The evaluated width of edge states from the capacitance is much larger than the magnetic length and the cyclotron radius expected from the one-electron picture. This wide width of edge states can be explained by the compressible-incompressible strip model, in which the screening effect is taken into account. Further the bulk conductivity of less than 10-12 S (S=1/Ω) is measured by the capacitance of the Corbino geometry sample, where the edge states are absent and the capacitance is determined by only σxx in this geometry. The localization of the bulk state is investigated by the obtained σxx.

Recent Developments in Magnetotransport Theory

A selection of topics recently examined in the literature of normal, dissipative magnetotransport is reviewed here, principally from the perspective of the Lei-Ting balance equation approach. We employ this isothermal formalism to revisit linear and nonlinear bulk 3D magnetoresistance, discussing longitudinal impurity limited conduction and magnetophonon resonance structure. For the transverse configuration, the characteristic linear impurity magnetoresistance log-divergence is seen to be removed by nonlinearity alone, with or without screening. At high magnetic fields, prominent hot-electron magnetophonon resonance structure is discussed for transverse transport as well as thermal noise. Another principal focus of concern here is the role of Landau quantization in linear and nonlinear transport in semiconductor microstructures, particularly quantum well superlattices (Type-I and Type-II) and heterostructures, including magnetoplasmon and cyclotron resonances as well as Shubnikov-de Haas oscillations. Electron-hole drag and negative absolute minority carrier mobility are discussed. Finally, we briefly discuss the density modulated 2DEG having magnetoresistance commensurability oscillations due to the interplay of the length scales of the cyclotron radius and the modulation period (superposed as an envelope upon Shubnikov-de Haas oscillations).

“Molecular Properties” in Intense Magnetic Field

The simple LCAO method has been used to find the effect of intense magnetic fields on the internuclear distance and the binding energy of the H2+ ion. The Spruch functions of the Hydrogen atom have been chosen as the basis. The results show that the magnetic pressure greatly affects the internuclear distance and the bonding energy. Req and Ebind as a function of α, the classical cyclotron radius of the electron, are given.