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1
Content available remote

Wave Functions of Disordered Two-Dimensional Electron Gas in Strong Magnetic Field

100%
Wysokiński K., Brenig W.
|
EN
The wave functions of the disordered two-dimensional electron gas (2DEG) placed in strong perpendicular magnetic field are calculated numerically. Even though the purpose of this work is mainly pedagogical, we shall shortly discuss our motivation which is possible application of the results to the calculations of the conductivity tensor in transition region between consecutive plateaus of the Hall conductivity in the quantum Hall effect.
2
Content available remote

Conductance of a Quantum Wire with Finite Length

80%
Suhrke M., Wilke S., Keiper R.
Acta Physica Polonica A
|
1991
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vol. 79
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issue 2-3
217-220
EN
The conductance of a ballistic quantum wire between two reservoirs exhibits steps of height 2e^{2}/h, if the occupation of transverse subbands is changed. We investigate conditions for observation of these steps starting from Kubo-Greenwood formula. We show how the conductance steps are influenced by the properties of the external regions as well as by the nature of the connection between these regions and the wire. Furthermore we incorporate residual scattering in long wires.
3
Content available remote

Photoemission by Polarized X-Rays

80%
Tilinin I. S.
Acta Physica Polonica A
|
1997
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vol. 91
|
issue 5
887-892
EN
The angular distribution of photoelectrons excited by X-rays is strongly correlated with the degree and type of polarization of incident photons. The angular and energy spectrum of signal photoelectrons leaving a solid is considerably modified as compared to the differential photoelectric cross-section owing to elastic and inelastic collisions the electrons suffer on their way out of a target. In this report an analytical expression for the angular distribution of photoelectrons escaping from the sample without being scattered inelastically was found in the transport approximation. The dependence of the angular distribution on the parameters characterizing optical orientation and polarization of incident X-rays was studied in detail.
4
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Quasiparticle Formation and Decay in Pulsed Photoexcitation of Disordered Semiconductors

80%
Kalvová A., Velický B.
Acta Physica Polonica A
|
1997
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vol. 92
|
issue 4
809-814
EN
The quasiparticle states in strongly illuminated semiconductors are light hybridized electron and hole states, Galickii quasiparticles. Their properties, especially if they are photoexcited at small detunings, may be rather complex. A protracted formation period is followed by quantum beats of two decaying resonances corresponding to both sides of the hybridization gap. On an example of elastic scattering on an alloy disorder, these phenomena are demonstrated and analyzed in terms of poles of the retarded Green function and the corresponding residuals.
5
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Inelastic Electron Tunneling Spectroscopy of a Mn Dimer

80%
Delgado F., Fernández-Rossier J.
Acta Physica Polonica A
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2012
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vol. 122
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issue 2
304-306
EN
A scanning tunneling microscope can probe the inelastic spin excitations of single magnetic atoms in a surface via spin-flip assisted tunneling. A particular and intriguing case is the Mn dimer case. We show here that the existing theories for inelastic transport spectroscopy do not explain the observed spin transitions when both atoms are equally coupled to the scanning tunneling microscope tip and the substrate, the most likely experimental situation. The hyperfine coupling to the nuclear spins is shown to lead to a finite excitation amplitude, but the physical mechanism leading to the large inelastic signal observed is still unknown. We discuss some other alternatives that break the symmetry of the system and allow for larger excitation probabilities.
6
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A Theoretical Analysis of Ballistic Electron Emission Microscopy: Band Structure Effects and Attenuation Lengths

80%
de Andres P., Reuter K., Garcia-Vidal F., Flores F., Hohenester U., Kocevar P.
Acta Physica Polonica A
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1998
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vol. 93
|
issue 2
281-287
EN
Using a quantum mechanical approach, we compute the ballistic electron emission microscopy current distribution in reciprocal space to compare experimental and theoretical spectroscopic I(V) curves. In the elastic limit, this formalism is a "parameter-free" representation of the problem. At low voltages, low temperatures, and for thin metallic layers, the elastic approximation is enough to explain the experiments (ballistic conditions). At low temperatures, inelastic effects can be taken into account approximately by introducing an effective electron-electron lifetime as an imaginary part in the energy. Ensemble Monte Carlo calculations were also performed to obtain ballistic electron emission microscopy currents in good agreement with the previous approach.
7
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Coherence of Electron Photoexcitation by Extremely Short Strong Light Pulses

80%
Kalvová A., Velický B.
Acta Physica Polonica A
|
1998
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vol. 94
|
issue 3
374-378
EN
For a semiconductor alloy with a predominant disorder scattering, we show that, under appropriate conditions, electrons photoexcited by a short strong light pulse form a coherent transient at first, while the incoherently backscattered electrons take over only gradually, with a time lag comparable with the pulse duration. The time evolution of the electron distribution is obtained by a direct evaluation of the non-equilibrium Green function.
8
Content available remote

Signal Photoelectron Yield Dependence on the X-Ray Angle of Incidence

80%
Tilinin I. S., Jabłoński A., Lesiak-Orłowska B.
Acta Physica Polonica A
|
1994
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vol. 86
|
issue 5
853-859
EN
The photoelectron emission from solids irradiated by X-rays was described by the analytical theory of electron transport and simulated by the Monte Carlo technique. The medium energy electron transport problem is treated by means of a Boltzmann type kinetic equation satisfying appropriate boundary conditions. The solution of the transport equation was obtained in the transport approximation based on the generalized radiative field similarity principle. Simple and reliable formalism was derived for both the differential and the total photoelectron yields. The dependence of the photoelectron yield on the X-ray incidence angle and the "flattening" effect of multiple elastic scattering on the angular distribution of electrons leaving the target are analysed in detail. The photoelectron yields and angular distributions calculated by the Monte Carlo algorithm, based on a realistic differential elastic scattering cross-section, are in good agreement with the results found from analytical theory. It is shown that main characteristics of the photoelectron emission are determined primarily by two parameters: the inelastic and the transport mean free paths.
9
Content available remote

Mean Escape Depth of Signal Photoelectrons from Amorphous and Polycrystalline Solids

80%
Tilinin I. S., Jabłoński A., Lesiak-Orłowska B.
Acta Physica Polonica A
|
1994
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vol. 86
|
issue 5
845-852
EN
Escape depth of photoelectrons leaving a target without being scattered inelastically was submitted to extensive theoretical analysis. Dependence of the mean escape depth on the X-ray angle of incidence and the electron initial angular distribution inside the sample was considered. The Monte Carlo algorithm was developed basing on a differential elastic scattering cross-section calculated within the partial-wave expansion method and a realistic electron-atom interaction potential. The mean escape depth was evaluated by means of the depth distribution function found analytically by solving a kinetic equation and by the Monte Carlo technique. The agreement between the results obtained from two methods is excellent. Elastic scattering was found to reduce considerably the escape depth. This reduction may reach up to 25% in the case of heavy elements in the practical X-ray photoelectron spectroscopy analysis. It was shown that the mean escape depth expressed in units of the electron transport mean free path is a universal function of the ratio of the inelastic to the transport mean free paths, the asymmetry parameter and the X-ray angle of incidence. A simple explicit expression for this function is proposed.
10
Content available remote

Peierls Instability and Charge-Density-Wave Transport in Fluoranthene and Perylene Radical Cation Salts

80%
Brütting W., Riess W.
Acta Physica Polonica A
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1995
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vol. 87
|
issue 4-5
785-790
EN
Fluoranthene and perylene radical cation salts are quasi-one-dimensional conductors, which show a Peierls transition to a charge-density-wave ground state. Radical cation salts with different stoichiometries composed of the aromatic donor molecules fluoranthene (Fa = C_{16}H_{10}) or perylene (Per = C_{20}H_{12}) and the counterion X¯ = PF¯_{6} were investigated. We find that the temperature dependence of the electrical conductivity and the properties in the charge-density-wave ground state strongly depend on the composition of the crystals. When fluoranthene is replaced by perylene, the Peierls transi­tion is shifted from 180 K to 120 K and the ground state energy gap decreases from values of 120-180 meV to 60-80 meV. In the charge-density-wave ground state the threshold field for nonlinear conductivity varies between 0.1 and 1 V/cm for different systems. Our results indicate that disorder, three-dimensional coupling and commensurability effects play an important role for the transport properties of these systems.
11
Content available remote

Dielectric and Ac Conductivity Studies of Mn-Doped Na_{1.86}Li_{0.10}K_{0.04}Ti_3O_7 Ceramics

61%
Singh R., Shripal
|
|
vol. 125
|
issue 1
67-72
EN
Dielectric-spectroscopic and ac conductivity studies on 0.01 and 1.0 molar percentage manganese doped layered Na_{1.86}Li_{0.10}K_{0.04}Ti_3O_7 ceramics have been reported. The dependence of loss tangent (tan δ) and relative permittivity (ε_{r}) on temperature in the range 350-775 K and on frequency in the range 10 kHz-1 MHz have been undertaken. The losses are the characteristics of dipole mechanism, electrical conduction and space charge polarization. The obtained conductivity plots between log(σ_{ac}T) versus 1000/T have been divided into four regions namely region I, II, III, and IV. The mechanism of conduction in region I is acknowledged to electronic hopping conduction. The less frequency and more temperature dependent region II is ascribed as a mixed mechanism "associated interlayer ionic conduction, electron hopping, and alkali ion hopping conduction". The unassociated interlayer ionic conduction along with alkali ion hopping conduction mechanisms are contributing to the transport process in the mid temperature region III. The mechanism of conduction in the highest temperature region IV may be recognized as the modified interlayer ionic conduction. The conductivity versus frequency curves lead to conclude that the electronic hopping conduction diminishes with the rise of temperature.
12
Content available remote

On the 2D Quantum Tunneling

51%
Mohammadpour H.
Acta Physica Polonica A
|
2016
|
vol. 130
|
issue 3
769-772
EN
In this paper, we have solved a quantum tunneling problem for 2-dimensional systems, including electron gas and graphene. In spite of the one-dimensional scattering problems, in two dimensions, we observe phenomenon of tunneling at energies above the barrier. This effect is an analogue to the total internal reflection in optics. The scattering amplitudes inside the barrier region exhibit decaying behavior corresponding to optical evanescent-wave coupling, not only in energies below barrier height, but also above barrier. Velocity-selecting transmission, corresponding to angle-resolved beam filtering effect is one of the achievements of the paper. The famous Hartman effect which occurs normally at sub-barrier energies and has previously been studied for graphene is also addressed. The results manifest occurrence of the Hartman effect for over-barrier energies, as well.
13
Content available remote

Theoretical calculations of the temperature dependence of the electrical and thermal conductivities of liquid gallium

51%
El-Daher M., Murphy R.
Open Physics
|
2005
|
vol. 3
|
issue 2
186-189
EN
The electrical and thermal resistivities of liquid gallium are calculated over a range of temperatures above the melting point using the solutions of the Boltzmann equation. The experimental x-ray structure factor of Waseda and the form factor derived using the Heine-Abarenkov model potential are used in these calculations. The ratio of the electrical and thermal conductivities is calculated and compared to experimental values and to the theoretical Lorenz number.
14
Content available remote

Rate-equation calculations of the current flow through two-site molecular device and DNA-based junction

51%
Walczak K.
|
EN
Here we present the calculations of incoherent current flowing through the two-site molecular device as well as the DNA-based junction within the rate-equation approach. Selected phenomena of interest are discussed in detail. The structural asymmetry of a two-site molecule results in a rectification effect, which can be neutralized by an asymmetric voltage drop at the molecule-metal contacts due to coupling asymmetry. The results received for the poly(dG)-poly(dC) DNA molecule reveal the coupling-and temperature-independent saturation effect of the current at high voltages, establishing for short chains the inverse square distance dependence. Additionally we document the conductance peak shifting in the direction of higher voltages due to a temperature decrease.
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