Papers by Vassilios Vargiamidis
Physical Review B, 2005
We calculate the conductance through a Gaussian impurity potential in a quantum wire using the Li... more We calculate the conductance through a Gaussian impurity potential in a quantum wire using the Lippmann-Schwinger equation. The impurity has a decay length d along the propagation direction while it is localized along the transverse direction. In the case of a repulsive Gaussian impurity it is shown that the conductance quantization is strongly affected by the decay length. In particular, increasing d causes gradual suppression of backscattering and smaller contribution of evanescent modes, leading to progressively sharper conductance steps. The dependence of the conductance on the impurity position is also examined. In the case of an attractive Gaussian impurity it is shown that multiple quasibound states are formed due to the finite size of the impurity. By varying the size of the impurity these quasibound states may evolve into highly localized states with greatly enhanced lifetime. It is also shown ͑for a model impurity potential very similar to the Gaussian͒ that the transmission exhibits asymmetric Fano line shape. Under certain circumstances the Fano line shape may appear "inverted" or evolve into a Breit-Wigner dip. We consider also the effects of the cross-sectional shape of the wire on the quantum transmission. It is shown that varying the cross-sectional shape causes shifting of the positions of the conductance steps ͑which is due to the rearrangement of the transverse energy levels͒ and influences the character of conductance quantization.
Physical Review B, 2007
Temperature dependence of the Fano effect in quantum wires with short-and finite-range impurities... more Temperature dependence of the Fano effect in quantum wires with short-and finite-range impurities. Vassilios Vargiamidis * and Hariton M. Polatoglou Department of Physics, Aristotle University, GR-54124 Thessaloniki, Greece. ...
Physical Review B, 2003
Shape effects on scattering in quantum wires with a transverse magnetic field. Vassilios Vargiami... more Shape effects on scattering in quantum wires with a transverse magnetic field. Vassilios Vargiamidis and Hariton M. Polatoglou Department of Physics, Aristotle University, GR-54124 Thessaloniki, Greece. Received 30 January 2003; published 9 June 2003 ...
We investigate the effect of an external uniform transverse electric field on the Fano resonance ... more We investigate the effect of an external uniform transverse electric field on the Fano resonance in electronic transport of a quantum wire with a finite range impurity. We employ the Feshbach coupled-channel theory for calculating the transmission probability. The attractive impurity is Pöschl-Teller along the propagation direction but is an arbitrary function of the lateral coordinate. For this type of
We analyze the relation between the density of states obtained from the energy derivative of the ... more We analyze the relation between the density of states obtained from the energy derivative of the Friedel phase (or the scattering matrix) and that obtained from the Green's function of quasi-one-dimensional systems with a double delta-function scattering potential. In the case of repulsive scatterers, we show that the local Friedel sum rule is valid when a correction term is included.
Electronic transport through a straight parabolically confined quantum wire with an attractive im... more Electronic transport through a straight parabolically confined quantum wire with an attractive impurity and a transverse electric field is investigated via the Feshbach coupled-channel theory. The impurity is modeled by a delta-function potential in the propagation direction while it is Gaussian in the transverse direction. In the presence of an impurity, the transmission probability of the wire may exhibit resonances
Physica E: Low-dimensional Systems and Nanostructures, 2010
Electronic transport through a straight, parabolically confined, quantum wire with an attractive ... more Electronic transport through a straight, parabolically confined, quantum wire with an attractive impurity and a transverse electric field is investigated via the Feshbach coupled-channel theory. The impurity is modeled by a δ- function potential in the propagation direction while it is Gaussian in the transverse direction. In the presence of an impurity, the transmission probability of the wire may exhibit resonances of the Fano type (which is the result of the interference between background transmission and transmission via a quasibound state created in the impurity). It is shown here that increasing the field strength from zero causes displacement of the confining potential, thereby inducing a “shifting” of the impurity across the channel and therefore influencing the resonance structure. As the center of the confining potential approaches the center of the impurity, the coupling of the (first) propagating state with the quasibound state of the second channel gradually decreases, resulting in a decrease of the resonance width. For a particular value of the field strength the resonance width shrinks to zero and the Fano profile collapses. The resonance energy is also examined as a function of the electric field strength.
Physical Review B, 2003
Shape effects on scattering in quantum wires with a transverse magnetic field. Vassilios Vargiami... more Shape effects on scattering in quantum wires with a transverse magnetic field. Vassilios Vargiamidis and Hariton M. Polatoglou Department of Physics, Aristotle University, GR-54124 Thessaloniki, Greece. Received 30 January 2003; published 9 June 2003 ...
Superlattices and Microstructures, 2006
We study GaN/AlN Quantum Dot (QD) superlattices utilizing the STREL environment which allows the ... more We study GaN/AlN Quantum Dot (QD) superlattices utilizing the STREL environment which allows the building of atomistic models, relaxation of the structures, the calculation of the electronic states and optical transitions and the visualization of the results. The forces are ...
Physical Review B, 2005
Resonances in electronic transport through a quantum wire with impurities and variable cross-sect... more Resonances in electronic transport through a quantum wire with impurities and variable cross-sectional shape. Vassilios Vargiamidis * and Hariton M. Polatoglou Department of Physics, Aristotle University, GR-54124 Thessaloniki, Greece. ...
Physical Review B, 2005
We calculate the conductance through a Gaussian impurity potential in a quantum wire using the Li... more We calculate the conductance through a Gaussian impurity potential in a quantum wire using the Lippmann-Schwinger equation. The impurity has a decay length d along the propagation direction while it is localized along the transverse direction. In the case of a repulsive Gaussian impurity it is shown that the conductance quantization is strongly affected by the decay length. In particular, increasing d causes gradual suppression of backscattering and smaller contribution of evanescent modes, leading to progressively sharper conductance steps. The dependence of the conductance on the impurity position is also examined. In the case of an attractive Gaussian impurity it is shown that multiple quasibound states are formed due to the finite size of the impurity. By varying the size of the impurity these quasibound states may evolve into highly localized states with greatly enhanced lifetime. It is also shown ͑for a model impurity potential very similar to the Gaussian͒ that the transmission exhibits asymmetric Fano line shape. Under certain circumstances the Fano line shape may appear "inverted" or evolve into a Breit-Wigner dip. We consider also the effects of the cross-sectional shape of the wire on the quantum transmission. It is shown that varying the cross-sectional shape causes shifting of the positions of the conductance steps ͑which is due to the rearrangement of the transverse energy levels͒ and influences the character of conductance quantization.
Physical Review B, 2007
Temperature dependence of the Fano effect in quantum wires with short-and finite-range impurities... more Temperature dependence of the Fano effect in quantum wires with short-and finite-range impurities. Vassilios Vargiamidis * and Hariton M. Polatoglou Department of Physics, Aristotle University, GR-54124 Thessaloniki, Greece. ...
Physical Review B, 2006
Fano resonance and persistent current in mesoscopic open rings: Influence of coupling and Aharono... more Fano resonance and persistent current in mesoscopic open rings: Influence of coupling and Aharonov-Bohm flux. Vassilios Vargiamidis * and Hariton M. Polatoglou Department of Physics, Aristotle University, GR-54124 Thessaloniki, Greece. ...
physica status solidi (c), 2008
Page 1. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim pss current topics in solid state p... more Page 1. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim pss current topics in solid state physics c status solidi www.pss-c.com physica Fano effect in quasi-one-dimensional wires with short-or finite-range impurities ...
physica status solidi (b), 2003
ABSTRACT We apply the Lippmann-Schwinger equation for obtaining the scattering amplitudes and con... more ABSTRACT We apply the Lippmann-Schwinger equation for obtaining the scattering amplitudes and conductance as a function of Fermi energy for electrons scattering from one and two point defects in a two-dimensional quantum wire. Further, we discuss the first and higher-order Born approximation to the scattering wave function and show that keeping five terms in the Born series can lead to a convergent wave function (except for Fermi energy close to the subband energy where it naturally diverges). It has been stated previously that electron transmission through a single point defect in a quantum wire is perfect at every subband minima independent of where the scatterer is located. However, here we demonstrate that perfect transmission at subband minima is strongly affected by the transversal position of the defect. In particular, we show that the perfect transparency effect is modified when the scatterer is located at the nodes of a normal confinement mode.
Materials Science and Engineering: B, 2000
We study two-dimensional (2D) modulated nanowires of length L and width N atoms. The modulated qu... more We study two-dimensional (2D) modulated nanowires of length L and width N atoms. The modulated quantum wire is connected to both sides with two semi-infinite perfectly ordered wires. We study the conductance of the modulated nanowires as a function of the degree of modulation and the Fermi energy of the electron. We employ the tight-binding approximation for the off-diagonal matrix elements of the Hamiltonian in order to describe the quantum wire and a many-channel Landauer formula in order to find its conductance. We present results for the above modulated nanowires where the diagonal matrix elements take values randomly from a set of two energies.
Journal of Physics: Conference Series, 2005
Page 1. Conductance of a quantum wire with an attractive smooth impurity potential This article h... more Page 1. Conductance of a quantum wire with an attractive smooth impurity potential This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2005 J. Phys.: Conf. Ser. 10 89 (http://iopscience.iop.org/1742-6596/10/1/022) ...
Journal of Computational and Theoretical Nanoscience, 2010
Page 1. Delivered by Ingenta to: ? IP : 93.91.26.12 Sun, 03 Apr 2011 06:26:06 REVIEW Copyright © ... more Page 1. Delivered by Ingenta to: ? IP : 93.91.26.12 Sun, 03 Apr 2011 06:26:06 REVIEW Copyright © 2010 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Computational and Theoretical Nanoscience Vol. 7, 430453, 2010 ...
Journal of Applied Physics, 2002
We study the effects of the shape of the cross section of a three-dimensional quantum wire on ele... more We study the effects of the shape of the cross section of a three-dimensional quantum wire on electron scattering from a single point defect in the wire. The confinement of electrons is modeled by both hard- and soft-wall potentials. We find that as the degree of anisotropy of the cross section of the wire is increased intersubband electron scattering is
Journal of Applied Physics, 2011
Two important issues concerning the scattering phases in a quantum wire with an attractive scatte... more Two important issues concerning the scattering phases in a quantum wire with an attractive scatterer are investigated. We consider the case of two quasibound states which couple to a scattering channel and give rise to two Fano resonances. First, we examine the effects of temperature on the phase of the transmission amplitude and the Friedel phase. It is shown that temperature effects tend to smear sharp features of the transmission phase; namely, the phase drops become less than pi, and acquire finite widths which increase linearly in the low-temperature regime. The influence of temperature on the Friedel phase and density of states becomes stronger as the Fano resonance becomes narrower. Second, we examine the behavior of the Friedel phase when the energy of the incident electron crosses an infinitely narrow Fano resonance, forming bound state in the continuum. It is shown that the Friedel phase exhibits abrupt jump of pi at this energy. We discuss this odd behavior in relation to the Friedel sum rule and point out its consequences on the charge in the scattering region.
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Papers by Vassilios Vargiamidis