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1
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Signatures of Majorana States in Electron Transport through a Quantum Dot Coupled to a Topological Wire

100%
Stefański P.
Acta Physica Polonica A
|
2015
|
vol. 127
|
issue 2
198-200
EN
We consider theoretically a system composed of a quantum dot coupled to a topological superconducting wire. The dot, being in Coulomb blockade (CB) regime is additionally coupled to the normal leads. The topological wire hosts Majorana states, which, as we show, characteristically modifies conductance through the dot. An unpaired Majorana state in the wire causes a unique temperature dependence of zero bias conductance vs. gate voltage. It decreases in-between CB peaks and on the sides of the peaks from the plateau at ~ e²/2h when temperature increases. At the same time conductance increases at the CB peak positions. It is accompanied by zero bias anomaly in differential conductance. For finite overlap of Majorana states in the wire the zero bias anomaly disappears. Instead, two characteristic Fano resonances of opposite symmetry appear, positioned mirror-symmetrically with respect to zero bias.
2
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Spin Dependent Fano Resonances in a Rashba System with Coulomb Interactions

100%
Stefański P.
Acta Physica Polonica A
|
2011
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vol. 119
|
issue 5
644-647
EN
The effects of interplay of interference of quantum mechanical electron waves and their mutual Coulomb interactions are investigated in the device composed of interacting quantum dot attached to polarized leads via quantum point contacts with the Rashba interaction. The Zeeman-split dot sub-levels form two interfering channels and as a result spin dependent Fano resonances arise in the conductance through the system. The Coulomb repulsion between the channels modifies the width and shape of the Fano resonances as compared to the non-interacting case. We formulate the Fano expression dependent on the dot's occupancy regulated by the Coulomb interactions.
3
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Single-Ion Rare Earth Anisotropy in ThMn_{12}-Type Compounds

100%
Stefański P.
Acta Physica Polonica A
|
1994
|
vol. 85
|
issue 3
615-621
EN
The single-ion rare earth anisotropy was investigated in ThMn_{12}-type compounds. For this purpose the crystal electric field parameter values were studied. In these compounds, described by formula RFe_{12-x}T_{x}, R = rare earth, T = Ti, V, Cr, Mo, W and Si, the T atoms have strong crystallographic site preference changing the local crystal electric field potential which "sees" the rare earth ion. The crystal electric field potentials A^{0}_{2} were calculated considering this site preference. The summations were performed taking into account the nearest neighborhood of the rare earth ion according to the recent results of band structure calculations. The charges of the surrounding Fe and T atoms were established applying the chemical bond model proposed by Pauling. The absolute value of A^{0}_{2} decreases when the content of vanadium increases in 8(i) position, which is in agreement with experimental data. Localization of Si atoms in 8(j) and 8(f) causes a decrease in A^{0}_{2}. The ^{155}Gd Mössbauer spectroscopy data confirm this fact. Miedema's "macroscopic" atom model of cohesion in alloys was applied for interpretation of the role of T atoms in the isomer shift and volume effects.
4
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Majorana States in Presence of Electron Interactions: Spinful Fractional Josephson Junction with a Quantum Dot

100%
Stefański P.
Acta Physica Polonica A
|
2018
|
vol. 133
|
issue 3
362-365
EN
We consider a fractional Josephson junction mediated by a quantum dot in which the Zeeman field arising from the magnetic fields driving left and right wires into topological phase can be tuned. Both fields, forming an angle Θp, can be rotated in the common plane perpendicular to the spin-orbit field in the wires. For Θp=0 the dot can be regarded as effectively non-interacting due to the large Zeeman splitting, whereas for Θp ≤sssimπ electron interactions are switched on the dot, affecting Majorana states. The tunnel electrode, weakly coupled to the dot from the top, allows to probe their density of states via conductance measurement. We show that electron interactions renormalize Majorana peak and introduce characteristic asymmetry in the gate voltage dependence of the transverse zero-bias conductance through the dot.
5
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Probing Fractional Josephson Junction with a Quantum Dot

100%
Stefański P.
Acta Physica Polonica A
|
2016
|
vol. 130
|
issue 2
554-557
EN
We consider theoretically a junction between two topological superconducting wires, mediated by a quantum dot. The wires are modelled by the Kitaev chains tuned into topological phase, which possess unpaired Majorana states at their ends. We derive the low energy Hamiltonian of the model. The Majorana states closer to the dot convert into the Dirac fermion inside the dot, forming fractional Josephson junction. The dot is additionally weakly coupled to the normal tunneling probe allowing transport measurement through the dot. When the topological wires are short, the unpaired Majorana end-states can hybridize inside the wire forming an extended Dirac fermionic state. It yields the destruction of the extended state in the dot. We discuss the dependence of the spectral density of the dot and its conductance on superconducting phase. We show that the conservation of parity of the junction, crucial for successful measurement of the fractional effect, can be assured by the gate voltage manipulation of the dot level position and that in case of an unpaired Majorana state in the junction a half conductance quantum can be observed.
6
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Level Occupancy Anomalies in a Double QD System

100%
Stefański P.
Acta Physica Polonica A
|
2009
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vol. 115
|
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
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Coqblin-Schrieffer Impurity with Local Exchange Coupling: a Perturbative Approach

100%
Stefański P.
Acta Physica Polonica A
|
2000
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vol. 97
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issue 3
385-388
EN
The Coqblin-Schrieffer one-impurity model with the additional local exchange interaction is studied within diagrammatic approach. The Ruderman-Kittel-Kasuya-Yoshida-type local exchange interaction between f electrons of the impurity and a channel of conduction electron l=0 partial waves is treated in the molecular field approximation. The perturbation expansion resummation for the Coqblin-Schrieffer hybridization mediated interaction vertex part is carried out in the ladder approximation yielding the formula for the Kondo temperature T_{K} decreasing with increased local exchange. Moreover, the temperature divergence of the susceptibility at T_{K} is shifted towards T=0. For some critical strength of the local exchange interaction the susceptibility approaches a Curie-type dependence as for an uncompensated impurity magnetic moment. A relation to the "Kondo disorder" model, which leads to the non-Fermi-liquid behavior, is discussed.
8
Content available remote

Ground State Properties of Tb^{3+} Ion in TbNi_{10}Si_{2}

51%
Stefański P., Suski W., Wochowski K., Mydlarz T.
Acta Physica Polonica A
|
1997
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vol. 92
|
issue 2
281-284
EN
Ground state properties of Tb^{3+} ion were investigated in the tetragonal ThΜn_{12}-type TbNi_{10}Si_{2} compound on the basis of temperature dependence of the paramagnetic susceptibility and magnetization measurements. The rare earth temperature dependence of the susceptibility was calculated using the Van Vleck equation. The Γ_{t5}^{(1)} doublet is suggested to be a ground state separated by 9 K from the first excited singlet Γ_{t1}^{(2)}. The magnetic moment associated with the ground state doublet agrees with saturation magnetization data at 4.2 K. The overall crystal field splitting is estimated to be 105 K.
9
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Content available

Interplay of Kondo and Fano Resonance in Electronic Transport in Nanostructures

51%
Bułka B., Stefański P., Tagliacozzo A.
Acta Physica Polonica A
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2005
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vol. 108
|
issue 4
555-569
EN
Quantum interference and electronic correlations are processes relevant for electronic transport in nanostructures. We present theoretical studies of transport for various models, which take into account these processes and describe the Fano resonance as well as many-body effects like the Kondo resonance. The results are compared with transport measurements performed on a small quantum dot strongly coupled to electrodes, a large semi-open quantum dot, a side-attached quantum dot to a quantum wire systems and a quantum dot embedded in the metallic ring. We show how conductance characteristics of the Kondo and the Fano resonance are modified in different situations.
10
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Spin Reorientation and Exchange Coupling in the Dy_{1-x}Er_{x}Fe_{10}Si_{2} Compounds

45%
Stefański P., Kowalczyk A., Skoryna D., Szlaferek A., Wrzeciono A.
Acta Physica Polonica A
|
1994
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vol. 85
|
issue 2
259-262
EN
The structural and magnetic properties of Dy_{1_{x}}Er_{x}Fe_{10}Si_{2} are investigated. X-ray analysis reveals that these compounds are of the tetragonal ThMn_{12} structure. In this structure the rare earth atoms occupy one crystallographic position 2(a). The unit cell contains 26 atoms. The spin reorientation temperature, T_{SR}, was measured from the temperature dependence of the initial susceptibility using an ac bridge of mutual inductance of the Harsthorn type. Dy^{+3} and Er^{+3} have opposite contributions to the entire magnetic anisotropy. The spin reorientation temperature is found to be about 271 K in DyFe_{10}Si_{2} and 48 K in ErFe_{10}Si_{2}. The values are discussed applying the crystal field model. The value of the rare earth-transition metal exchange coupling constant J_{RFe}/k_{B} derived from the mean-field model analysis of the Curie temperature is about -13 K. The Fe-Fe exchange integral is much higher and is equal to about 75 K.
11
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Content available

Relationship between pH of ruminal fluid during subacute ruminal acidosis and physiological response of the Polish Holstein-Friesian dairy cows

39%
Stefańska B., Pruszyńska-Oszmałek E., Szczepankiewicz D., Stajek K., Stefański P., Gehrke M., Nowak W.
Polish Journal of Veterinary Sciences
|
2017
|
issue 3
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