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  1. 55 Acta Physica Polonica A

  2. 2 Open Physics

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  4. 8 2015

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  1. 6 Bułka B.

  2. 6 Weymann I.

  3. 5 Barnaś J.

  4. 4 Domański T.

  5. 4 Donabidowicz A.

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1
Content available remote

Many-Channel Landauer-Like Conductance Formula in a Uniform Magnetic Field

100%
Benamira F., Abdellaoui A.
Acta Physica Polonica A
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2012
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vol. 122
|
issue 4
721-724
EN
Linear-response theory is combined with the Landauer viewpoint to describe quantitatively transport in a four-lead mesoscopic structure within the presence of a uniform magnetic field. A new multichannel magnetoconductance formula is derived in the case where the magnetic field is perpendicular to the current-flow. The invariance under magnetic reversal test is confirmed.
2
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Two-Dimensional Analytical Threshold Voltage Modelling of Pseudomorphic Si_{0.8}Ge_{0.2} p-Channel MOSFETs

100%
Ansaripour G.
Acta Physica Polonica A
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2011
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vol. 120
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issue 6
1043-1046
EN
In this work we present an analytical model of the threshold voltage of SiGe p-channel metal oxide semiconductor field effect transistor based on the solution of the two-dimensional Poisson's equation and the ground state wave function of Fang and Howard, and taking into account the space charge in the channel and its effect on the surface potential. It is seen that the experimental data are well fitted within the experimental error that shows the appropriateness of the implemented model. Also comparing the calculated results to that of the calculated from the available recent reported models indicates a reasonable improvement to them.
3
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Mutual Inductance and Selfinductance in Mesoscopic Systems

63%
Zipper E., Dajka J., Szopa M.
Acta Physica Polonica A
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2002
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vol. 102
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issue 3
419-428
EN
The role played by the magnetostatic interaction in mesoscopic multichannel systems is discussed. We show that the interaction of currents from different channels, when taken in the selfconsistent mean field approximation, leads to selfinductance terms in the Hamiltonian producing an internal magnetic flux. Such multichannel systems can exhibit spontaneous flux or flux expulsion. The dependence of these phenomena on the parameters of the system is discussed.
4
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Hartree-Fock Simulation of Persistent Current in Rings with Single Scatterer

63%
Németh R., Moško M.
Acta Physica Polonica A
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2005
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vol. 108
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issue 5
795-801
EN
Using the self-consistent Hartree-Fock approximation for spinless electrons at zero temperature, we calculate the persistent current of the interacting electron gas in a one-dimensional ring containing a singleδ barrier. Our results agree with correlated models like the Luttinger liquid model and lattice model with nearest-neighbor interaction. The persistent current is a sine-like function of magnetic flux. It decays with the ring length (L) faster than L^{-1} and eventually like L^{-α-1}, where α>0 is universal.
5
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Quantum-Interference Semiconductor Devices Revisited

63%
Figielski T.
Acta Physica Polonica A
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2001
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vol. 99
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issue 6
699-708
EN
First, a simple semiclassical approach has been applied to the problem of a quantum phase acquired by an electron carrying both the charge and spin, which travels in an electromagnetic field. Basic hypothetical devices whose operation relies on the quantum interference, including spin-related interference, are discussed in the following. Finally, experimental results demonstrating two-beam interference in a planar quantum dot are presented.
6
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Influence of Magnetic Field on Dark States in Transport through Triple Quantum Dots

63%
Wrześniewski K., Weymann I.
Acta Physica Polonica A
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2017
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vol. 132
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issue 1
108-111
EN
We theoretically study the electronic transport through a triple quantum dot system in triangular geometry weakly coupled to external metallic leads. By means of the real-time diagrammatic technique, the current and Fano factor are calculated in the lowest order of perturbation theory. The device parameters are tuned to such transport regime, in which coherent population trapping of electrons in quantum dots due to the formation of dark states occurs. The presence of such states greatly influences transport properties leading to a strong current blockade and enhanced, super-Poissonian shot noise. We consider both one- and two-electron dark states and examine the influence of magnetic field on coherent trapping in aforementioned states. When the system is in one-electron dark state, we observe a small shift of the blockade's region, whereas in the case of two-electron dark state, we show that strong magnetic field can lift the current blockade completely.
7
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Tunneling of Interacting Fermions in 1D Systems

63%
Gendiar A., Moško M., Vagner P., Németh R.
Acta Physica Polonica A
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2005
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vol. 108
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issue 4
661-667
EN
Using the self-consistent Hartree-Fock approximation for spinless electrons at zero temperature, we study tunneling of the interacting electron gas through a single δ barrier in a finite one-dimensional wire connected to contacts. Our results exhibit features known from correlated many-body models. In particular, the conductance decays with the wire length as ∝ L^{-2α}, where the powerα is universal. We also show that a similar result for a wire conductance can be extracted from the persistent current (I) through theδ barrier in a one-dimensional ring, where it is known that I∝ L^{-1-α}.
8
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Current Shot Noise and Bunching of Electrons in Multilevel Quantum Dots

63%
Michałek G., Bułka B.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
27-30
EN
Currents and their fluctuations in multilevel quantum dots are studied theoretically in the limit of sequential tunneling. The spin degrees of freedom, many-body electronic states (singlet and triplet) as well as relaxation processes between the levels of the quantum dots are considered. In general, due to the rapid relaxation processes the shot noise is sub-Poissonian, however for a large polarization of the outgoing currents from the singlet and triplet states one gets the super-Poissonian type of the shot noise due to the bunching of tunneling events.
9
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Terahertz Generation and Detection by Plasma Waves in Nanometer Gate High Electron Mobility Transistors

63%
Knap W., Łusakowski J., Teppe F., Dyakonova N., Meziani Y.
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EN
The high electron mobility transistors can act as a resonator cavity for the plasma waves that can reach THz frequencies for a nanometer size devices. As was predicted by Dyakonov and Shur in 1993, the steady state of the current flow in a gated 2D electron gas can become unstable leading to the emission of an electromagnetic radiation at the plasma wave frequencies. The theory predicted also that the plasma waves can be used for resonant detection of THz electromagnetic radiation. In the present paper we review our recent experiments on THz emission and detection performed on high electron mobility transistors based on different semiconductor structures: InGaAs/GaAlAs, GaAs/GaAlAs, and Si.
10
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Asymmetry Induced Localization

51%
Kohler H.
Acta Physica Polonica A
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2013
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vol. 124
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issue 6
1053-1059
EN
We consider a two-level system, which couples via non-commuting operators to two independent oscillator baths. When the coupling is symmetric, the renormalized hopping matrix element is finite even for infinitely strong coupling strength. The two-level system is in a delocalized phase. For finite coupling strength a localization transition occurs for a critical asymmetry angle, which separates the localized from the delocalized phase. Using the method of flow equations we are able to monitor real time dynamics.
11
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Electronic Transport through a Bending Contact

51%
Schröter U.
Acta Physica Polonica A
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2006
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vol. 109
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issue 3
305-310
EN
The so-called "break-junction technique" allows us to realize contacts only single-atom in diameter at their thinnest point. Electronic transport through such narrow constrictions shows a quantum mechanical signature which is well described in a transport channel picture. Each individual contact is characterized by an ensemble of channel transmission probabilities. Preferred total conductance values as well as the number of channels, however, turn out to be universal for the material investigated, despite the lack of control of the exact contact geometry.
12
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Coherent Transport through Systems of Coupled Quantum Dots

51%
Trocha P., Barnaś J.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
473-480
EN
Spin-dependent electronic transport through two coupled single-level quantum dots attached to ferromagnetic leads with parallel and antiparallel magnetizations is analyzed theoretically. The intra-dot Coulomb correlation is taken into account, while the inter-dot Coulomb repulsion is omitted. Conductance and tunnel magnetoresistance associated with magnetization rotation are calculated by the nonequilibrium Green function technique. The relevant Green functions are derived by the equation of motion method in the Hartree-Fock approximation. The dot occupation numbers and the Green functions are calculated self-consistently. The interference effects in electronic transport through quantum dots are analyzed in two different configurations. It is shown that the Fano resonance in conductance can be observed even for vanishing inter-dot hopping parameter t. The interplay of the interference effects and the Coulomb interactions in quantum dots is also analyzed.
13
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Thermoelectric and Interference Effects in a Kondo-Correlated Quantum Dot with Rashba Spin-Orbit Coupling

51%
Karwacki Ł., Trocha P., Barnaś J.
Acta Physica Polonica A
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2013
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vol. 124
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issue 5
901-904
EN
Thermoelectric effects in spin-polarized transport through a strongly correlated quantum dot coupled to two ferromagnetic leads is investigated theoretically by means of the finite-U slave boson technique. The dot is coupled to the leads both symmetrically via the spin-conserving tunneling processes and asymmetrically via spin-nonconserving Rashba-induced tunneling terms. The asymmetric coupling leads to various interference effects which modify transport properties. We have analyzed such thermoelectric coefficients like the electronic contribution to heat conductance κ, thermopower S, and thermoelectric efficiency ZT.
14
Content available remote

The In-Gap Charge Current through the Correlated Quantum Dot Hybridized with Superconductor

51%
Donabidowicz A., Domański T.
Acta Physica Polonica A
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2008
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vol. 114
|
issue 1
75-82
EN
We explore the Andreev tunnelling through the strongly correlated quantum dot embedded between the normal and superconducting electrodes. For a small external voltage |eV| <∆_s the electron arriving from the normal lead can be converted into a pair on the quantum dot and further propagates in the superconducting lead while simultaneously the hole is reflected back to the normal electrode. Conductance of such anomalous current is very sensitive to the particle-hole mixing of the quantum dot spectrum. We analyze the influence of the proximity effect and the Coulomb interactions on the differential Andreev conductance focusing on the extreme limit ∆_s → ∞.
15
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Spin-Dependent Transport through SU(4) Kondo Dot in the Presence of Spin-Flip Processes

51%
Krychowski D., Lipiński S.
|
|
issue 5
955-956
EN
The spin-resolved current of carbon nanotube quantum dot coupled to ferromagnetic electrodes and influenced by spin-flip scattering is studied in the Kondo regime by the equation of motion method.
16
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Different Quantization Mechanisms in Single-Electron Pumps Driven by Surface Acoustic Waves

51%
Utko P., Gloos K., Bindslev Hansen J., Sørensen C., Lindelof P.
Acta Physica Polonica A
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2006
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vol. 110
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issue 3
403-408
EN
We have studied the acoustoelectric current in single-electron pumps driven by surface acoustic waves. We have found that in certain parameter ranges two different sets of quantized steps dominate the acoustoelectric current versus gate-voltage characteristics. In some cases, both types of quantized steps appear simultaneously though at different current values, as if they were superposed on each other. This could indicate two independent quantization mechanisms for the acoustoelectric current.
17
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Current Suppression in Transport Through Triple Quantum Dots Coupled to Ferromagnetic Leads

51%
Wrześniewski K., Weymann I.
Acta Physica Polonica A
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2015
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vol. 127
|
issue 2
460-462
EN
We consider transport through triple quantum dot system in a triangular geometry weakly coupled to external ferromagnetic leads. The real-time diagrammatic technique in the lowest order perturbation theory is used to calculate the current and Fano factor in the parallel and antiparallel magnetic configuration of the system as well as the resulting tunnel magnetoresistance (TMR). We focus on the transport regime where the current is suppressed and show that it can lead to negative differential conductance and large super-Poissonian shot noise, which are present in both magnetic configurations. Furthermore, we show that for voltages where the system is trapped in a one-particle dark state the TMR becomes suppressed, while for two-particle blockade, the TMR is much enhanced.
18
Publication available in full text mode
Content available

Electron Transport through Double Quantum Dots with Interdot Coulomb Repulsion

51%
Sztenkiel D., Świrkowicz R.
Acta Physica Polonica A
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2006
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vol. 110
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issue 3
389-394
EN
Electron transport through a system of two quantum dots connected in series is studied theoretically with the use of non-equilibrium Green function formalism based on the equation of motion method. Each dot is described by the one-level Anderson Hamiltonian and interdot Coulomb interactions in the form of the Hubbard-like term are taken into account. The electric current and occupation numbers are calculated with the use of two different approaches. The results of the methods are compared and discussed in detail. Strong asymmetry of I-V characteristics with respect to bias voltage reversal are obtained when energy levels of the dots are not aligned.
19
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Dark States and Transport through Quantum Dots

51%
Tooski S., Bułka B.
Acta Physica Polonica A
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2012
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vol. 121
|
issue 5-6
1231-1233
EN
We consider current through triple and quadruple quantum dot systems in an in-plane electric field and in the sequential tunneling regime. The electric field breaks symmetry of the system and can trap electron in a dark state in which current flow can completely be blocked. Consequently rotating the electric field, one can observe current oscillations and blockades due to dark state.
20
Content available remote

Electrostatic Gates for GaN/AlGaN Quantum Point Contacts

51%
Czapkiewicz M., Cywiński G., Dybko K., Siekacz M., Wolny P., Gierałtowska S., Guziewicz E., Skierbiszewski C., Wróbel J.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
1026-1028
EN
We report on AlGaN/GaN quantum point contacts fabricated by using e-beam lithography and dry ion etching. The tunable nano-constrictions are defined by the integration of side and top gates in a single device. In this configuration, the planar gates are located on the both sides of a quantum channel and the metallic top gates, which cover the active region, are separated from the substrate by an insulating and passivating layers of HfO_2 or Al_2O_3/HfO_2 composite. The properties of devices have been tested at T = 4.2 K. For side gates we have obtained a very small surface leakage current I_g< 10^{-11} A at gate voltages |V_g| < 2 V, however, it is not enough to close the quantum channel. With top gates we have been able to reach the pinch-off voltage at V_g = - 3.5 V at a cost of I_g ≈ 10^{-6} A, which has been identified as a bulk leakage current.
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