Dynamical exchange corrections to the dielectric function in a two-dimensional electron gas

The effect of dynamical exchange interactions on the dielectric function of a two-dimensional electron gas is studied using a variational approach. Exchange effects are introduced via the local-field correction. The variationally obtained local-field factor is compared to the earlier perturbative result to first order in the electron-electron interaction.     

Dynamical exchange corrections to the dielectric function in a two-dimensional electron gas

The effect of dynamical exchange interactions on the dielectric function of a two-dimensional electron gas is studied using a variational approach. Exchange effects are introduced via the local-field correction. The variationally obtained local-field factor is compared to the earlier perturbative result to first order in the electron-electron interaction.     

Dynamical relativistic corrections to the leptonic decay width of heavy quarkonia

We calculate the dynamical relativistic corrections, originating from radiative one-gluon exchange, to the leptonic decay width of heavy quarkonia in the framework of a covariant formulation of light-front dynamics. Comparison with the non-relativistic calculations of the leptonic decay width of J = 1 charmonium and bottomonium S-ground states shows that relativistic corrections are large. Most importantly, the calculation of these dynamical relativistic corrections legitimate a perturbative expansion in , even in the charmonium sector. This is in contrast with the ongoing belief based on calculations in the non-relativistic limit. Consequences for the ability of several phenomenological potentials to describe these decays are described. Received: 6 December 2001 / Published online: 5 April 2002     

Quantum corrections to the conductance of n-GaAs films in a strong magnetic field

The conductance of doped n-GaAs films is studied experimentally as a function of magnetic field and temperature in strong magnetic fields right up to the quantum limit (ħω_c = E _F). The Hall conductance G _xy is virtually independent of temperature T until the transverse conductance G _xx is quite large compared with e ²/h. In strong fields, when G _xx becomes comparable to e ²/h, G _xy starts to depend on T. The difference between the conductances G _xx at the two temperatures 4.2 and 0.35 K depends only weakly on the magnetic field H over a wide range of magnetic fields, while the conductances G _xx themselves vary strongly. The results can be explained by quantum corrections to the conductance as a result of the electron-electron interaction in the diffusion channel. The possibility of quantization of the Hall conductance as a result of the electron-electron interaction is discussed. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 3, 201–206 (10 February 1998)     

Recoil corrections to elastic electron scattering in the Breit approximation

Recoil corrections to the cross sections for elastic electron scattering from spin-0 nuclei are investigated in the Breit approximation. The form of the scattering amplitude in first- and second-Born approximation is investigated in detail using time-dependent perturbation theory, and it is found that the center-of-mass (CM) frame is particularly convenient to work in. Transformation equations relating the lab and CM frames are developed. Those parts of the second-Born amplitude which correspond to the Breit amplitude are isolated, and the Breit equation with the electromagnetic Breit interaction is investigated in detail. Corrections to the scattering cross sections which are inversely proportional to the nucleus mass (recoil corrections) are calculated. Numerical results are presented for the particular case of ¹⁶O.     

Quantum corrections to the conductance of AlGaAs/GaAs-based quasiballistic quantum wires

Quantum conductance corrections (QCCs) due to weak localization and interaction effects of quantum quasiballistic wires are investigated for the first time. At temperatures in the range 2 K<T<12 K a crossover of these corrections from one-dimensional behavior to zero-dimensional behavior is observed. It is shown that the phase coherence length in the wires studied is less than the length L _T =(ℏD/kT)^1/2 at all temperatures. It is found that the conventional theory of QCCs describes correctly the experimental temperature dependence of the QCCs but gives a much lower value than the experimental one. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 12, 973–976 (25 June 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Dynamical nature of chaos in electron systems of high-T c superconductors

A model of the fermion-condensation phase transition forming a plateau in the spectrum of single-particle excitations near the Fermi surface at T=0 is used to analyze those features of the spectral functions of normal states of high-T _c superconductors which are inherent in a marginal Fermi liquid contaminated by impurities. With this model, such a behavior is shown to be due to the fermion condensate, which acts as an impurity subsystem because its energy spectrum at T=0 is dispersionless. The influence of the anisotropy of condensate distribution in the Brillouin zone on the spectral functions is discussed.     

Many-body corrections to the effective electron mass in the noble metals

The electronic mass enhancement from the electron-phonon interaction is calculated for the noble metals from data on the electric conductivity and is found to be 10–15%. A brief discussion of many-body effects in band calculations is also given.     

Control of electron conductance by means of mobile impurities in metal-oxide-metal systems

The paper is concerned with the proposal of a qualitative model of conductance mechanisms in M-O-M systems which is based on shifts of ionized impurities in an amorphous oxide layer under the influence of an external field. These impurities do not contribute immediately to current conduction as the carriers do but they control the transport of electrons by influencing the field distribution inside the dielectric.From this model there necessarily follows the existence of a region of high field near the cathode, and of a region of negative resistance on the volt-ampere characteristic. Further it leads to V-A characteristics consisting predominantly of ohmic sections. The origin of theseV-A characteristics is shifted after a change of polarity has been brought about regardless of the nominal polarity. Experimental results obtained by measuring the V-A characteristics of concrete Al-Al₂O₃-Al and Al-SiO_x-Al systems deliberately contamined by Na⁺ ions lead to a qualitative agreement with the conclusions drawn from the model as regards the ohmic character of the V-A characteristics and their displacement with the change of polarity.     

A model for engineering the electrical conductance at nanoscale

With the emergence of nanoelectronics faster and denser circuits are being produced, this largely because the aggressive scaling to the nanometer range of the insulating film used as dielectric. Moreover, enhancements of the electrical conductivity of nanofiller based composites can be achieved by the incorporation of conductive nanofillers into polymer matrix. In such systems electron wave-function penetration into the dielectric is important as it leads to undesired or desired leakage currents by tunneling respectively. Therefore, a proper design of the electrical conductance in such structures becomes important in order to control accurately their performance. In this research, a model for engineering the electrical conductance of resistors at nanoscale is presented. The conductance at infinitesimal bias of nanoresistors is modeled within the framework of Landauer's tunneling which results in an exponential integral function for the total electrical conductance. Model takes the effects of azimuthal and inclination angles between nanocontacts into account, as well as the effect of the thickness of the dielectric layer. The model also unveils a U-shaped behavior of the electrical conductance as a function of the azimuthal angle between nanocontacts. As a result, a minimal electrical conductance is predicted when the azimuthal angle reaches 90°.     

Enhancement of conductance fluctuations in two-dimensional mesoscopic electron systems with valley structures

Conductance fluctuations are studied in twodimensional mesoscopic electron system with a two-hold valley degeneracy (n _v =2), which corresponds to the inversion layer of Si-MOSFET formed in (1,0,0) plane. It is shown that the intervalley scattering modifies conductance fluctuations depending on the ratio, Min { _c , _T }/ _v , where _v = ( – 2)/2 and _c , _T , and are, respectively, system traversal time, thermal diffusion time, intervalley scattering time and total life time of electrons. Conductance fluctuations are no longer universal and vary from G _univ 0.862·e ²/h to {ie223-5} at low temperatures even for isotropic systems. The conductance fluctuations increase with decreasing system size, increasing electron density and increasing intervalley scattering time. The effect of intervalley scattering is essentially the same as that of intersubband scattering as previously reported. At finite temperatures where _{T c} , the intervalley scattering modifies the fluctuations through the change in the energy correlation range to results in the reduction of the conductance fluctuations. In Si-MOSFET formed in (1, 1, 1) plane, wheren _v =6, more enhanced fluctuations are expected. Experimental studies are desired on theoretically predicted points.     

Quantum corrections to the conductance of a square quantum dot with soft confinement

We study the conductance of a square quantum dot, modeling the potential with a self-consistent Thomas-Fermi approximation. The resulting potential is characterized by level statistics indicative of mixed chaotic and regular electron dynamics within the dot in spite of the regular geometry of the gates defining the dot. We calculate numerically, for the case of a quantum dot with soft confinement, the weak localization (WL) correction. We demonstrate that this confining potential may generate either Lorentzian or linear lineshapes depending on the number of modes in the leads. Finally, we present experimental WL data for a lithographically square dot and compare the results with numerical calculations. We analyze the experimental results and numerical simulations in terms of semiclassical and random matrix theory (RMT) predictions and discuss their limitations as far as real experimental structures are concerned. Our results indicate that direct application of the above predictions to distinguish between chaotic and regular dynamics in a particular cavity can not always lead to reliable conclusions as the shape and magnitude of the WL correction can be strongly sensitive to the geometry-specific, non-universal features of the system. Received 13 May 1998     

The Bahcall corrections to electron capture and the Hartree-Fock rearrangement

The Bahcall correction factorsX ^L/K andX ^M/L forL/K andM/L electron capture ratio respectively are calculated including the Hartree-Fock (HF) rearrangement. The rearrangement takes into account that the atom after the electron capture is not in the HF ground state. The selfconsistent single electron orbits for the excited states with a hole in theK,L orM shell are calculated using the Herman-Skillman and the Froese HF codes. The rearrangement changes the correction factor into the right direction, but the reduction is too small. Only for very light atoms the alteration is larger than 1% and therefore it is in general smaller than the present experimental errors.     

Relativistic corrections to electron scattering by the deuteron and triton

Relativistic corrections to electron-deuteron and electron-³He scattering have been calculated. the deuteron corrections agree substantially with the results of Gross and the ³He corrections are approximately equal in magnitude to those of Cocho and Flores.     

Relativistic corrections to the electric polarizability of compound systems

The widely used relation alpha; = alpha(0)+Deltaalpha for the electric polarizability, where Deltaalpha is proportional to the r.m.s. charge radius of the system, is revisited within a simple model of two spinless particles bound electromagnetically. A complete set of the relativistic corrections to alpha(0) following from the Breit Hamiltonian is obtained. It is shown that these corrections modify the result for alpha; in comparison to that obtained with alpha(0) taken in the nonrelativistic approximation. We propose that the same situation can take place in the more complicated case of hadrons. Special attention is devoted to the correct definition of the center-of-mass coordinates which are found to be very important.