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  1. 35 Acta Physica Polonica A

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  1. 5 Weymann I.

  2. 4 Jantsch W.

  3. 4 Wilamowski Z.

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1
Content available remote

Carrier Spin Dephasing during Spin-Preserving Tunneling in Coupled Quantum Dots

100%
Krzykowski M., Gawełczyk M., Machnikowski P.
Acta Physica Polonica A
|
2016
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vol. 130
|
issue 5
1165-1168
EN
In this contribution we study carrier tunneling in a system consisting of a pair of coupled quantum dots. We predict the presence of a spin dephasing channel in such a system, which is associated with a "welcher-weg" type of decoherence process occurring during carrier tunneling. In our model such a process is caused by a mismatch of g-factor values in two quantum dots in the presence of external magnetic field. This leads to a mismatch in spin Zeeman splitting between the dots and, in consequence, to the distinguishability of phonons emitted during the tunneling of carriers with opposite spins. Thus we demonstrate a process of spin dephasing without any direct spin-environment coupling present in the model.
2
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Accuracy of Effective Mass Equation for a Single and Double Cylindrical Quantum Dot

100%
Mielnik-Pyszczorski A., Gawarecki K., Machnikowski P.
Acta Physica Polonica A
|
2017
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vol. 132
|
issue 2
376-379
EN
In this contribution we study the accuracy of various forms of electron effective mass equation in reproducing spectral and spin-related features of quantum dot systems. We compare the results of the standard 8 band k·p model to those obtained from effective mass equations obtained by perturbative elimination procedures in various approximtions for a cylindrical quantum dot or a system of two such dots. We calculate the splitting of electronic shells, the electron g-factor and spin-orbit induced spin mixing and show that for a cylindrical dot the g-factor is reproduced very exactly, while for the two other quantities the effective mass equation is much less accurate.
3
Publication available in full text mode
Content available

Bychkov-Rashba Effect and g-Factor Tuning in Modulation Doped SiGe Quantum Wells

100%
Malissa H., Jantsch W., Mühlberger M., Schäffler F., Wilamowski Z., Draxler M., Bauer P.
Acta Physica Polonica A
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2004
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vol. 105
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issue 6
585-590
EN
We investigate the spin resonance of electrons in one-sided modulation doped Si_{1-x}Ge_x (x=0-10%)) quantum wells defined by Si_{0.75}Ge_{0.25} barriers. In such structures, the Bychkov-Rashba effect induces an effective magnetic field in the quantum well layer which causes anisotropy of both the g-factor and the spin coherence time. Evaluation of the Rashba coefficient as a function of x yields a monotonic increase. For x=5% the shift in the resonance field exceeds the ESR linewidth already, demonstrating the possibility to use this effect for g-factor tuning to select individual spins in an ensemble.
4
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Lateral Spin Diffusion Probed by Two-Color Hanle-MOKE Technique

80%
Quast J., Astakhov G., Ossau W., Molenkamp L., Heinrich J., Höfling S., Forchel A.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1311-1316
EN
We report on all optical spatially resolved spin diffusion experiments in an unstrained, unbiased n-GaAs layer. Optical pump and probe intensities are varied over a wide range to study the impact of optical disturbance on spin transport. Both quantities have a considerable influence on the measured spin diffusion length and spin lifetime. Furthermore, an effective spin diffusion coefficient was obtained as a function of temperature.
5
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The Edelstein Effect in the Presence of Impurity Spin-Orbit Scattering

80%
Maleki Sheikhabadi A., Raimondi R., Shen K.
Acta Physica Polonica A
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2017
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vol. 132
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issue 1
135-139
EN
In this paper we study the current-induced spin polarization in a two-dimensional electron gas, known also as the Edelstein effect. Compared to previous treatments, we consider both the Rashba and Dresselhaus spin-orbit interaction as well as the spin-orbit interaction from impurity scattering. In evaluating the Kubo formula for the spin polarization response to an applied electric field, we explicitly take into account the side-jump and skew-scattering effects. We show that the inclusion of side-jump and skew-scattering modifies the expression of the current-induced spin polarization.
6
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Magnetic Field Sensor Based on Magnetic Tunnel Junction with Voltage-Tunable Magnetic Anisotropy

80%
Skowroński W., Wiśniowski P., Wrona J., Żywczak A., Stobiecki T.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
496-498
EN
We present a submicron magnetic field sensor with voltage-tunable magnetic field sensitivity. The device, based on magnetic tunnel junction, exhibits high tunnelling magnetoresistance ratio of up to 90%. Perpendicular magnetic anisotropy of thin ferromagnetic sensing layer in combination with an in-plane magnetized reference layer is used to obtain linear change in the sensor resistance in response to the in-plane magnetic field. The perpendicular anisotropy is further controlled by the bias voltage and, thus, the sensitivity of the sensor is changed. In addition, we evaluate the sensor selectivity for the magnetic field direction and present an influence of the temperature on the anisotropy.
7
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Spin-Dependent Transport through a Single-Wall Carbon Nanotube Quantum Dot with an S=1 Molecule

80%
Płomińska A., Weymann I.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
475-477
EN
Transport properties of an S=1 molecule attached to a single-wall carbon nanotube quantum dot, which is coupled to two external ferromagnetic leads, are analyzed in the sequential tunneling regime. The magnetizations of the leads are assumed to form either a parallel or an antiparallel magnetic configuration. The calculations are performed by using the real-time diagrammatic technique in the lowest order perturbation theory with respect to the tunnel coupling. It is shown that the presence of the molecule strongly affects the bias voltage dependence of the current and differential conductance in both magnetic configurations, as well as the resulting tunnel magnetoresistance. Negative (greatly enhanced) tunnel magnetoresistance is found in the case of antiferromagnetic (ferromagnetic) coupling between the nanotube and molecule.
8
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Optical Investigation of ZnO Nanowires

80%
Martínez-Criado G., Hernández-Vélez M., Letard I., Cros A., Cantarero A., Mínguez-Bacho I., Susini J., Tucoulou R., Sans J., Sanz R., Vázquez M.
Acta Physica Polonica A
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2010
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vol. 117
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issue 2
369-373
EN
In this study we report the application of synchrotron X-ray fluorescence, photoluminescence and Raman scattering techniques to the analysis of the incorporation of impurities in unintentionally doped ZnO nanowires. Highly ordered one-dimensional ZnO arrays were fabricated by an oxidation process of Zn metal electrodeposited in nanoporous anodic alumina template. X-ray fluorescence data show the contribution of residual elements into the ZnO nanowires growth. A rough analytical quantification of the main light and heavy chemical contents derives impurity concentrations below 1%. The optical efficiency of ZnO nanowires is strongly affected by non-radiative centers up to temperatures as low as 100 K. The photoluminescence was found to be totally dominated by optical transitions associated with the anodic alumina template. Finally, the Raman scattering provides no evidence of local vibrational modes or secondary phases, but it shows the unambiguous signature of the ZnO hexagonal phase.
9
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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
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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.
10
Content available remote

Spin Conductance of the Quantum Wire

80%
Dargys A.
Acta Physica Polonica A
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2008
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vol. 113
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issue 3
937-942
EN
Spin transport in a semiconducting quantum wire connected to two spin-unpolarized electron reservoirs is investigated. The spin-orbit interaction is included via the Rashba Hamiltonian which together with the Zeeman Hamiltonian determines spin-filtering properties of the wire. The spin current as a function of the voltage was found to have an oscillatory or growing character.
11
Content available remote

Current-Induced Magnetic Dynamics in Asymmetric Ferromagnetic Single-Electron Devices

80%
Kowalik M.
Acta Physica Polonica A
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2009
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vol. 115
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issue 1
290-292
EN
The theoretical calculations of possible dynamics for a localized magnetic moment of the central electrode in ferromagnetic single-electron devices are presented. The spin-transfer torque from spin current absorbed by the central electrode is calculated. Thereafter, an in-plane component of spin torque is regarded during the integration of the Landau-Lifshitz-Gilbert equation and the time evolution of the localized magnetic moment of the central electrode is obtained. The necessary conditions for switching of the magnetic moment are discussed.
12
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Unzipped and Defective Nanotubes: Rolling up Graphene and Unrolling Tubes

80%
Chico L., Santos H., Ayuela A., Jaskólski W., Pelc M., Brey L.
Acta Physica Polonica A
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2010
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vol. 118
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issue 3
433-441
EN
The properties of carbon nanotubes can be dramatically altered by the presence of defects. In this work we address the properties of two different kinds of defective nanotubes: junctions of achiral tubes with topological defects and partially unzipped carbon nanotubes. In particular, we begin by focussing on the interface states in carbon nanotube junctions between achiral tubes. We show that their number and energies can be derived by applying the Born-von Karman boundary condition to an interface between armchair- and zigzag-terminated semi-infinite graphene layers. We show that these interface states, which were thought to be due to the presence of topological defects, are in fact related to the graphene zigzag edge states. Secondly, we study partially unzipped carbon nanotubes, which can be considered as the junction of a carbon nanotube and a graphene nanoribbon, which has edge features giving rise to novel properties. Carbon nanoribbons act as transparent contacts for nanotubes and viceversa, yielding a high conductance. At certain energies, nanoribbons behave as valley filters for carbon nanotubes; this holds considering electron-electron interaction effects. Furthermore, the application of a magnetic field turns the system conducting, with a 100% magnetoresistance. These novel structures may open a way for new carbon-based devices.
13
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Limitations in the Tunability of the Spin Resonance of 2D Electrons in Si by an Electric Current

80%
Wilamowski Z., Malissa H., Glazov M., Jantsch W.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
375-379
EN
We analyse the recently observed effect of an in-plane electric current through a Si quantum well on the conduction electron spin resonance. We find that the ratio of resonance shift and current density is independent of temperature and dissipation processes, but the channel current is reduced due to a parallel electric channel in heavily modulation doped samples. The inhomogeneous current distribution results in some broadening of the ESR line width. In high mobility Si/SiGe layers the current induced increase in the electron temperature is considerably larger than the increase in the lattice temperature. The signal amplitude scales with the square of electron mobility.
14
Content available remote

Planar Hall Effect in Ferromagnetic (Ga,Mn)As/GaAs Superlattices

80%
Wesela W., Wosiński T., Mąkosa A., Figielski T., Sadowski J., Terki F., Charar S.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
369-373
EN
The planar Hall effect was used for investigation of magnetic anisotropy in short period (Ga,Mn)As/GaAs superlattices epitaxially grown on (001) oriented GaAs substrate. The results confirmed the existence of low-temperature magnetocrystalline anisotropy in the superlattices with the easy magnetic axes directed along the two in-plane 〈100〉 directions. Attention is paid to the two-state behaviour of the planar Hall resistance at zero magnetic field that provides its usefulness for applications in non-volatile memory devices.
15
Publication available in full text mode
Content available

D'yakonov--Perel Spin Relaxation Suppressed by an Applied Magnetic Field

80%
Wilamowski Z., Jantsch W.
Acta Physica Polonica A
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2003
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vol. 103
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issue 6
671-674
EN
We observe a strong anisotropy of spin relaxation and a decrease in the spin relaxation rate with increasing electron mobility in contrast to predictions of the classical D'yakonov-Perel spin relaxation model. We show that for high electron mobility the cyclotron motion causes an additional modulation of spin-orbit coupling, leading to an effective suppression of the spin relaxation rate.
16
Content available remote

Spin-Dependent Transient Effects in Electron Transport in the Quantum Dot System

80%
Parafiniuk P., Taranko R.
Acta Physica Polonica A
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2009
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vol. 116
|
issue 5
844-846
EN
We study the effects of the Coulomb interaction U between the electrons of opposite spins localized in the quantum dot on the time-dependent electron transport through the quantum dot coupled with two non-magnetic leads. We calculate the transient spin-dependent current generated by a pulsed bias voltage applied across the quantum dot system via the equation of motion method for appropriate correlation functions. The influence of the Coulomb interaction on the quantum coherent oscillations and beats of the current, spin current and current polarization ratio is studied. Our results indicate that the coherent beats in both the total and spin currents observed in the case of vanishing Coulomb interaction are strongly suppressed by non-zero Coulomb interaction. We also show that in the case of the pulsed bias almost fully polarized current occurs in some time windows for non-vanishing Coulomb interaction contrary to almost pure charge or spin current at vanishing U.
17
Content available remote

The Magnetic Field Effects on Spin Polarization of T-Shaped Double Quantum Dots Coupled to Ferromagnetic Leads

80%
Wójcik K., Weymann I.
Acta Physica Polonica A
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2015
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vol. 127
|
issue 2
222-224
EN
We analyze the spin-dependent conductance and spin polarization of a double quantum dot in a T-shape configuration coupled to ferromagnetic leads in the presence of external magnetic field. The calculations are performed with the aid of the numerical renormalization group method. We show that in the antiparallel configuration, finite magnetic field can give rise to the full spin polarization of the current, which can be controlled by tuning the dots' levels. On the other hand, for parallel configuration enhanced spin polarization can be generated by an exchange field due to the presence of ferromagnetic leads and can be also tuned by changing level position or external magnetic field. The magnetic field can be thus used to improve the spin-resolved properties of the system.
18
Publication available in full text mode
Content available

Spin-Dependent Tunneling in a Magnetic Field for Junctions Involving Normal and Superconducting CDW Metals

80%
Ekino T., Gabovich A., Suan Li M., Pękała M., Szymczak H., Voitenko A.
Acta Physica Polonica A
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2006
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vol. 109
|
issue 4-5
477-484
EN
The voltage, V, dependences of the differential tunnel conductance G(V) were calculated for two kinds of junctions involving normal and superconducting charge-density-wave metals (CDWMs) in the external magnetic field H. The first is a non-symmetrical junction with a CDWM electrode being biased with respect to a ferromagnet. Calculations show that the paramagnetic splitting occurs between spin-up and spin-down components of G(V), similar to what is observed when a superconducting electrode is used instead of the CDWM one. The second setup is symmetric (CDWM-I-CDWM), where I denotes an insulator. If at least one of the CDWM electrodes is normal and H≢0, G(V) will also be spin-split.
19
Content available remote

Inverse Edelstein Effect: an Heuristic Derivation

80%
Raimondi R., Shen K., Vignale G.
Acta Physica Polonica A
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2015
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vol. 127
|
issue 2
454-456
EN
We provide a heuristic derivation of the "Inverse Edelstein Effect" (IEE), in which a non-equilibrium spin accumulation in the plane of a two-dimensional (interfacial) electron gas drives an electric current perpendicular to its own direction. The drift-diffusion equations that govern the effect are derived and applied to the interpretation of recent experiments. A brief analysis based on the Kubo formula shows that the result is valid also outside the diffusive regime, i.e. when spin and momentum relaxation become comparable.
20
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Valence Band of Cubic Semiconductors from Viewpoint of Clifford Algebra

80%
Dargys A.
Acta Physica Polonica A
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2009
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vol. 116
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issue 2
226-231
EN
In this paper the properties of semiconductors having cubic symmetry are considered in a real multidimensional Euclidean space within the formalism of multivector Clifford algebra rather than, usually used for this purpose, complex Hilbert space. In particular, it is demonstrated how the valence band energy spectrum and spin properties may be calculated within Cl_5 Clifford algebra and SO(5) symmetry group related with it.
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