Momentum alignment and spin orientation of photoexcited electrons in quantum wells

PublishedThe momentum and spin distribution functions for electrons excited by polarized light incident normally to the heterostructure plane are determined for a quantum well with infinitely high walls. It is shown that for a low ratio of the light and heavy hole masses, an anomalously rapid growth of momentum alignment and a decrease of electron spin orientation occur with increase of their energy of motion in the plane of the well. The dependences on the exciting photon energy of the plane and circular polarizations of the hot luminescence in the pumping direction at it shortwave edge are found

Screening of a macroion by multivalent ions: A new boundary condition for Poisson-Boltzmann equation and charge inversion

Screening of a macroion by multivalent counterions is considered. It is shown that ions form strongly correlated liquid at the macroion surface. Cohesive energy of this liquid leads to strong additional attraction of counterions to the surface. Away from the surface this attraction is taken into account by a new boundary condition for the Poisson-Boltzmann equation. This equation is solved with the new boundary condition for a charged flat surface and a long cylinder. For a cylinder Onsager-Manning theory looses its universality so that apparent charge of the cylinder is smaller than their theory predicts and depends on its bare charge. It can also vanish or change sign.Comment: 4 pages, no figure

Magnetic field effect on tunnel ionization of deep impurities by terahertz radiation

A suppression of tunnelling ionization of deep impurities in terahertz frequency electric fields by a magnetic field is observed. It is shown that the ionization probability at external magnetic field, B, oriented perpendicular to the electric field of terahertz radiation, E, is substantially smaller than that at B || E. The effect occurs at low temperatures and high magnetic fields

Charge Fluctuations and Counterion Condensation

We predict a condensation phenomenon in an overall neutral system, consisting of a single charged plate and its oppositely charged counterions. Based on the ``two-fluid'' model, in which the counterions are divided into a ``free'' and a ``condensed'' fraction, we argue that for high surface charge, fluctuations can lead to a phase transition in which a large fraction of counterions is condensed. Furthermore, we show that depending on the valence, the condensation is either a first-order or a smooth transition.Comment: 16 pages, 1 figure, accepted to be published in PR

Counterion Condensation and Fluctuation-Induced Attraction

We consider an overall neutral system consisting of two similarly charged plates and their oppositely charged counterions and analyze the electrostatic interaction between the two surfaces beyond the mean-field Poisson-Boltzmann approximation. Our physical picture is based on the fluctuation-driven counterion condensation model, in which a fraction of the counterions is allowed to ``condense'' onto the charged plates. In addition, an expression for the pressure is derived, which includes fluctuation contributions of the whole system. We find that for sufficiently high surface charges, the distance at which the attraction, arising from charge fluctuations, starts to dominate can be large compared to the Gouy-Chapmann length. We also demonstrate that depending on the valency, the system may exhibit a novel first-order binding transition at short distances.Comment: 15 pages, 8 figures, to appear in PR

Effective interaction between helical bio-molecules

The effective interaction between two parallel strands of helical bio-molecules, such as deoxyribose nucleic acids (DNA), is calculated using computer simulations of the "primitive" model of electrolytes. In particular we study a simple model for B-DNA incorporating explicitly its charge pattern as a double-helix structure. The effective force and the effective torque exerted onto the molecules depend on the central distance and on the relative orientation. The contributions of nonlinear screening by monovalent counterions to these forces and torques are analyzed and calculated for different salt concentrations. As a result, we find that the sign of the force depends sensitively on the relative orientation. For intermolecular distances smaller than $6\AA$ it can be both attractive and repulsive. Furthermore we report a nonmonotonic behaviour of the effective force for increasing salt concentration. Both features cannot be described within linear screening theories. For large distances, on the other hand, the results agree with linear screening theories provided the charge of the bio-molecules is suitably renormalized.Comment: 18 pages, 18 figures included in text, 100 bibliog

Magnetic field effect on tunnel ionization of deep impurities by far-infrared radiation

The probability of electron tunneling from a bound to a free state in an alternating electric and a constant magnetic field is calculated in the quasiclassical approximation. It is shown that the magnetic field reduces the probability of electron tunneling. The application of the external magnetic field perpendicular to the electric field reduces the ionization probability at high magnetic fields, when cyclotron resonance frequency becomes larger than reciprocal tunneling time. The increase of electric field frequency to values larger than the same reciprocal tunneling time enhances the influence of magnetic field

Tunneling ionization of deep centers in high-frequency electric fields

A theoretical and experimental study of the tunneling ionization of deep impurities in semiconductors has been carried out for high-frequency alternating electric fields. It is shown that tunneling ionization occurs by phonon-assisted tunneling which proceeds at high electric field strengths into direct tunneling without involving phonons. In the quasistatic regime of low frequencies the tunneling probability is independent of frequency. Raising the frequency leads to an enhancement of the tunneling ionization. The transition from the quasistatic limit to frequency-dependent tunneling is determined by the tunneling time which, in the case of impurities interacting with thermal phonons, is controlled by the temperature. In both the quasistatic and high-frequency limits, the application of an external magnetic field perpendicular to the electric field reduces the ionization probability when the cyclotron frequency becomes larger than the reciprocal tunneling time