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  1. 59 Acta Physica Polonica A

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  1. 8 Bułka B.

  2. 6 Barnaś J.

  3. 6 Michałek G.

  4. 6 Rudziński W.

  5. 5 Domański T.

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1
Content available remote

Quasistationary Electron States for CdTe/ZnTe/CdTe Open Spherical Quantum Dots

100%
Stojanović D., Kostić R.
Acta Physica Polonica A
|
2010
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vol. 117
|
issue 5
768-771
EN
The energy spectra of an electron in open spherical quantum dot (QD) within the effective mass approximation (EMA) and rectangular potential model is presented. Energy structure of quantum dots is important because of their possible applications in electronic and optoelectronic devices. For proper description and interpretation of tunneling processes knowledge of resonant states of quantum dots is necessary. Energy values depend on parameter like size of system and spatial composition. The lifetimes of the quasistationary states are computed within the framework of the scattering S-matrix method. It is shown how core radius and barrier thickness for the CdTe/ZnTe/CdTe example influence electron states and their lifetimes.
2
Content available remote

The Calculation for Strain Distributions and Electronic Structure of InAs/GaAs Quantum Dots Based on the Eight-Band k·p Theory

100%
Shu C., Liu Y.
Acta Physica Polonica A
|
2016
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vol. 129
|
issue 3
371-377
EN
In order to analyze the strain distribution of InAs/GaAs quantum dot in a pyramidal geometry, the traditional calculation method is based on the single band envelope approximation with the modified band edge from the eight band k·p theory. In this paper, we use the eight band k·p Hamiltonian to calculate, and the piezoelectric effects and the electronic structure are also discussed subsequently. To this end, some necessarily derived formulae in calculations about using the finite element calculation software COMSOL are presented in this paper. The results show the details about strain distributions, piezoelectric effects and electronic structure of an InAs/GaAs pyramidal quantum dot, verify the feasibility and efficiency of the calculation method.
3
Content available remote

Effect of Retrapping on Thermoluminescence Peak Intensities of Small Amorphous Silicon Quantum Dots

100%
Debelo N., Dejene F., Mal'nev V., Senbeta T., Mesfin B., Roro K.
Acta Physica Polonica A
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2016
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vol. 129
|
issue 3
362-366
EN
The effect of retrapping on thermoluminescence intensity peak corresponding to each trap of small amorphous silicon quantum dots in three traps - one recombination center model is investigated. For first order kinetics, where there is no effect of retrapping, the thermoluminescence intensity clearly depends on the level of the trap beneath the edge of the conduction band. This energy difference between the edge of the conduction band and the level of the trap is called trap depth (activation energy). The shallowest trap gives the highest thermoluminescence intensity peak for first order kinetics. However, it was clearly observed that for second order and a case beyond second order kinetics, the thermoluminescence intensity peak corresponding to each trap does not depend on the trap depth. In this case, the retrapping probability coefficients are taken into account and most electrons which are detrapped from the shallow trap(s) will be retrapped to the deeper trap(s) resulting in fewer electrons taking part in the recombination process. This significantly reduces the thermoluminescence intensity peaks of the shallower trap(s). It was observed that the deepest trap, with very high concentration of electrons due to the retrapping phenomenon, gives the highest thermoluminescence intensity. In addition, the variation of concentration of electrons in each trap and the intensity of the thermoluminescence are presented. Though we considered the model of three traps and one recombination center, this phenomenon is true for any multiple traps.
4
Content available remote

Energy Band and Absorption Coefficient of Quantum Dots in a Well Structure

100%
Zhang P., Lu X., Zhang C., Yao J.
Acta Physica Polonica A
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2012
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vol. 122
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issue 1
197-201
EN
Building on the effective-mass envelope function theory, this paper focuses on the study of the energy band and the absorption coefficient of InAs/In_{x}Ga_{1 - x}As quantum dots in a well (DWELL) structure. In contrast to InAs/In_{0.15}Ga_{0.85}As quantum DWELL, the InAs/In_{0.2}Ga_{0.8}As quantum DWELL has lower ground states. With the thickness of In_{0.15}Ga_{0.85}As layer changing from 7 nm to 9 nm and In_{0.2}Ga_{0.8}As layer changing from 9 nm to 12 nm, the calculation shows that their absorption coefficient spectra takes a red shift in the long-wave infrared and far-infrared ranges, respectively. Moreover, when the thickness of the In_{x}Ga_{1 - x}As layer is defined as 9 nm, the absorption coefficient spectra of InAs/In_{0.2}Ga_{0.8}As DWELL shows a obvious red shift comparing with that of InAs/In_{0.15}Ga_{0.85}As DWELL.
5
Content available remote

Phonon-Assisted Excitation Transfer in Quantum Dot Molecules

100%
Rozbicki E., Machnikowski P.
Acta Physica Polonica A
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2007
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vol. 112
|
issue 2
197-202
EN
We derive a quantum-kinetic description of phonon-assisted Förster transfer between two coupled quantum dots (a quantum dot molecule). We show that the exciton state decays to the ground state of the quantum dot molecule via a combination of the Rabi rotation and exponential decay. For moderately spaced dots this process takes place on a picosecond timescale.
6
Content available remote

Level Occupancy Anomalies in a Double QD System

100%
Stefański P.
Acta Physica Polonica A
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2009
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vol. 115
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issue 1
92-94
EN
A double quantum dot system is considered in the presence of the electron intra-Coulomb U interactions within the dots and inter-Coulomb U_{12} interactions between them. We show that both for spinless and spinfull electrons the dots occupancy anomalies are encountered and caused by electron correlations. This non-monotonic behavior strongly deviates from usual level filling at the Coulomb blockade. For spinfull electrons the inter-dot interaction modifies also on-site electron correlations.
7
Content available remote

Electronic Transport through a Quantum Dot Coupled to Non-Collinear Ferromagnetic Electrodes: The Kondo Regime

100%
Świrkowicz R., Wilczyński M., Wawrzyniak M., Barnaś J.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
565-568
EN
Linear and non-linear conductance of quantum dots attached to magnetic leads is considered theoretically in the Kondo regime. The considerations are based on the non-equilibrium Green function formalism and the relevant equation of motion method. Splitting of the Kondo anomaly due to coupling of the dot to ferromagnetic electrodes, and its dependence on magnetic configuration of the system and on the lead's spin polarization is studied numerically.
8
Content available remote

Effect of Magnetic Zigzag Edges in Graphene-like Nanoribbons on the Thermoelectric Power Factor

80%
Krompiewski S., Cuniberti G.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
535-537
EN
This study shows that magnetic edge states of graphene-like nanoribbons enhance effectively the thermoelectric performance. This is due to the antiparallel alignment of magnetic moments on opposite zigzag edges and the confinement effect, which jointly lead to the appearance of a gap in the electronic energy spectrum. Consequently, the Seebeck coefficient as well as the thermoelectric power factor get strongly enhanced (with respect to other alignment cases) at room temperature and energies not far away from the charge neutrality point. Moreover the corresponding figure of merit (ZT) is also improved as a result of the reduced electronic thermal conductance.
9
Content available remote

Andreev Spectroscopy in Three-Terminal Hybrid Nanostructure

80%
Michałek G., Bułka B., Urbaniak M., Domański T., Wysokiński K.
Acta Physica Polonica A
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2015
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vol. 127
|
issue 2
293-295
EN
We consider a hybrid three-terminal structure consisting of a quantum dot coupled to three leads, two normal and one superconducting. The current flowing between one of the normal and the superconducting electrodes induces voltage in the other normal (floating) electrode. The value of the induced voltage depends on the position of the Andreev levels in the quantum dot and is a measure of the interplay between the electron transfer and the subgap anomalous reflection processes. When the crossed (i.e. non-local) Andreev reflections dominate the induced potential in the normal electrode becomes negative. This situation occurs for the relatively strong coupling to the superconducting electrode and only outside the Coulomb blockade region. Taking the superconducting electrode as the voltage probe one gets additional information on competition of injected carriers.
10
Content available remote

Spin Dependent Conductance of a Quantum Dot Side attached to Topological Superconductors as a Probe of Majorana Fermion States

80%
Krychowski D., Lipiński S., Cuniberti G.
Acta Physica Polonica A
|
2018
|
vol. 133
|
issue 3
552-554
EN
Spin-polarized transport through a quantum dot side attached to a topological superconductor and coupled to a pair of normal leads is discussed in Coulomb and Kondo regimes. For discussion of Coulomb range equation of motion method with extended Hubbard I approximation is used and Kondo regime is analyzed by Kotliar-Ruckenstein slave boson approach. Apart from the occurrence of zero bias anomaly the presence of Majorana states reflects also in splitting of Coulomb lines. In the region of Coulomb borders the spin dependent negative differential conductance is observed. Due to the low energy scale of Kondo effect this probe allows for detection of Majorana states even for extremely weak coupling with topological wire. In this range no signatures of Majorana states appear in Coulomb blockade dominated transport.
11
Content available remote

Threshold Effects in Three-Terminal Hybrid Systems

80%
Michałek G.
Acta Physica Polonica A
|
2014
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vol. 126
|
issue 1
224-225
EN
In the paper we study transport in the three terminal hybrid devices with quantum dot. Our attention is focused on the conductance threshold effects (so called Wigner singularities) caused by the back action from the side-wire. In particular we study influence of the direct electron transfer (ET) and crossed Andreev reflection (CAR) processes on the conductance caused by the direct Andreev reflection (DAR) processes.
12
Content available remote

Phonon-Assisted Kondo Resonance in Spin-Dependent Transport through a Quantum Dot

80%
Świrkowicz R., Wilczyński M., Barnaś J.
Acta Physica Polonica A
|
2009
|
vol. 115
|
issue 1
272-274
EN
Effects of local vibrational modes on electron transport through a quantum dot attached to ferromagnetic electrodes are studied in the Kondo regime by the non-equilibrium Green function formalism based on the equation of motion method. Differential conductance is calculated for parallel and antiparallel configurations of the leads' magnetic moments, and well defined Kondo resonance peaks and their phonon satellites are found. The influence of a compensating magnetic field on the peak positions is also discussed.
13
Content available remote

Cross-Correlations and Charge Pumping in Shot Noise οf Coupled Quantum Dot System

80%
Michałek G., Bułka B.
Acta Physica Polonica A
|
2009
|
vol. 116
|
issue 5
879-881
EN
We analyze current auto- and cross-correlations in the system of two capacitively coupled large quantum dots. Our attention is focused on the strong inter-dot coupling when an electron transfer through one of the quantum dots induces charge pumping through the second quantum dot. We show individual contributions to shot noise from various tunneling processes in the charge space.
14
Content available remote

Phonon-Assisted Tunneling of an Electron in a Strained Self-Assembled Quantum Dot Molecule

80%
Pochwała M., Machnikowski P.
Acta Physica Polonica A
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2008
|
vol. 114
|
issue 5
1285-1291
EN
We calculate phonon-assisted relaxation rates in a self-assembled quantum dot molecule. The calculation is based on wave functions obtained within an envelope function approach, including strain effects. The single-phonon relaxation is shown to be efficient for separations between the dots around 10 nm when, in addition, the dots are brought close to resonance.
15
Content available remote

Thermoelectric Effect in Photon-Assisted, Spin-Polarized Tunnelling through a Quantum Dot

80%
Bocian K., Rudziński W.
Acta Physica Polonica A
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2015
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vol. 127
|
issue 2
484-486
EN
Features of electric and thermal conductance, Seebeck coefficient as well as figure of merit in tunnelling through a single level quantum dot connected to external ferromagnetic leads are investigated theoretically using the equation of motion method within the nonequilibrium Green function technique. The influence of the harmonic ac field on the transport characteristics for the considered system is discussed in detail. In particular, it is shown that the photonic field strongly modulates the Seebeck coefficient, thus resulting in multi-peak structure of figure of merit. Thermoelectric phenomenon in a hybrid junction with the dot attached to two ferromagnetic and one superconducting lead is also discussed.
16
Content available remote

Spin Thermoelectric Effects in a Strongly Correlated Double Quantum Dot System

80%
Karwacki Ł.
Acta Physica Polonica A
|
2015
|
vol. 127
|
issue 2
478-480
EN
Spin thermoelectric effects through a strongly correlated double quantum dot system embedded in a Aharonov-Bohm ring coupled to two leads with Rashba spin-orbit coupling have been investigated theoretically by means of the finite-U slave-boson technique. This method provides a reliable description of electron transport through quantum dot systems in the low temperature regime T ≪ T_{K}, where T_{K} is the so-called Kondo temperature. Particular emphasis is put on the possibility of the so-called spin Seebeck effect in such a system as a more sensitive probe of the Kondo state.
17
Publication available in full text mode
Content available

Introduction to the Physics of Quantum Dots

80%
Kardynal B.
Acta Physica Polonica A
|
2001
|
vol. 100
|
issue 3
275-286
EN
Quantum dots contain only a few well-defined energy levels for electron and/or holes as a result of the confinement of charge in all three spatial dimensions. Here, we describe both the application of photoluminescence spectroscopy and transport measurements to the characterisation of quantum dots and the novel phenomena that they exhibit. These include the Coulomb blockade, single electron tunnelling and single photon detection. The impact of quantum dots on future electronics and directions for future research, such as in quantum computing and cryptography, are addressed.
18
Content available remote

Transport through Single-Wall Carbon Nanotubes Weakly Coupled to External Leads

80%
Weymann I., Krompiewski S., Barnaś J.
Acta Physica Polonica A
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2009
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vol. 115
|
issue 1
296-298
EN
We consider transport properties of single-wall metallic carbon nanotubes weakly coupled to external leads. In particular, we analyze the conductance and shot noise of nanotubes coupled to nonmagnetic leads and show that the shot noise may become super-Poissonian depending on the ground state of the nanotube. In addition, we also show that when the nanotube is coupled to one ferromagnetic and one nonmagnetic lead, it can operate as a gate-controlled spin diode.
19
Content available remote

Thermoelectric Transport through the Double Quantum Dot in the Sequential Tunneling Regime

80%
Szukiewicz B., Wysokiński K.
Acta Physica Polonica A
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2014
|
vol. 126
|
issue 5
1159-1162
EN
The charge and spin thermoelectric transport in the system composed of a central molecule in contact with two normal electrodes in an external magnetic field of the Zeeman type have been studied. Such system can support pure spin current for applications in spintronics. By appropriate gate tuning of each of the dots it is possible to electrically control the direction of the spin current or tune the device operating as a thermoelectric generator to optimal performance.It has been shown that the device is poor energy converter in the parameter region where its thermoelectric figure of merit attains very large values.
20
Content available remote

Noise Enhancement due to Telegraphic Switching in a Two-Level Quantum Dot Coupled to Spin-Polarized Leads

80%
Ptaszyński K.
Acta Physica Polonica A
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2018
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vol. 133
|
issue 3
526-528
EN
Current fluctuations in a two-level quantum dot coupled to the spin-polarized leads are studied by means of the Markovian master equation. It is shown, that transitions between spin configurations of the system cause switching between different current channels, which generates the super-Poissonian noise enhancement and the correlation between subsequent waiting times separating the successive tunneling events.
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