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587 results on '"Gudmundsson, Vidar"'

251. Electroluminescence Caused by the Transport of Interacting Electrons through Parallel Quantum Dots in a Photon Cavity.

Author

Gudmundsson, Vidar, Abdulla, Nzar Rauf, Sitek, Anna, Goan, Hsi‐Sheng, Tang, Chi‐Shung, and Manolescu, Andrei

Subjects
QUANTUM dots, ELECTROLUMINESCENCE, ELECTRON-phonon interactions, ELECTRON transport, PHOTON correlation, RESONANCE
Abstract

Abstract: We show that a Rabi‐splitting of the states of strongly interacting electrons in parallel quantum dots embedded in a short quantum wire placed in a photon cavity can be produced by either the para‐ or the dia‐magnetic electron‐photon interactions when the geometry of the system is properly accounted for and the photon field is tuned close to a resonance with the electron system. We use these two resonances to explore the electroluminescence caused by the transport of electrons through the one‐ and two‐electron ground states of the system and their corresponding conventional and vacuum electroluminescense as the central system is opened up by coupling it to external leads acting as electron reservoirs. Our analysis indicates that high‐order electron‐photon processes are necessary to adequately construct the cavity‐photon dressed electron states needed to describe both types of electroluminescence. [ABSTRACT FROM AUTHOR]

Published
2018
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252. Coulomb effects on the spin polarization of quantum rings

Author

MANOLESCU ANDREI, DADAY CSABA, and GUDMUNDSSON VIDAR

Subjects
QUANTUM RING,SPIN-ORBIT INTERACTION,COULOMB INTERACTION, Condensed Matter::Mesoscopic Systems and Quantum Hall Effect
Abstract

We consider electrons in a circular nanoring of zero width, in magnetic field, and with Rashba spin-orbit interaction. We include the Coulomb interaction in the the «exact diagonalization» manner. The Coulomb interaction has strong effects on the spin polarization which may be totally different than for noninteracting electrons. Our current results include up to four electrons, but this number can easily be increased.

Published
2011

254. Electron localization and optical absorption of polygonal quantum rings

Author

Ministerio de Economía y Competitividad (España), University of Iceland, Sitek, Anna, Serra, Llorenç, Gudmundsson, Vidar, Manolescu, Andrei, Ministerio de Economía y Competitividad (España), University of Iceland, Sitek, Anna, Serra, Llorenç, Gudmundsson, Vidar, and Manolescu, Andrei

Abstract

© 2015 American Physical Society. We investigate theoretically polygonal quantum rings and focus mostly on the triangular geometry where the corner effects are maximal. Such rings can be seen as short core-shell nanowires, a generation of semiconductor heterostructures with multiple applications. We show how the geometry of the sample determines the electronic energy spectrum, and also the localization of electrons, with effects on the optical absorption. In particular, we show that irrespective of the ring shape low-energy electrons are always attracted by corners and are localized in their vicinity. The absorption spectrum in the presence of a magnetic field shows only two peaks within the corner-localized state domain, each associated with different circular polarization. This picture may be changed by an external electric field which allows previously forbidden transitions, and thus enables the number of corners to be determined. We show that polygonal quantum rings allow absorption of waves from distant ranges of the electromagnetic spectrum within one sample.

Published
2015

269. Snaking states on a cylindrical surface in a perpendicular magnetic field

Author

University of Iceland, Icelandic Centre for Research, Ministerio de Economía y Competitividad (España), Manolescu, Andrei, Rosdahl, Tomas Orn, Erlingsson, Sigurdur I., Serra, Llorenç, Gudmundsson, Vidar, University of Iceland, Icelandic Centre for Research, Ministerio de Economía y Competitividad (España), Manolescu, Andrei, Rosdahl, Tomas Orn, Erlingsson, Sigurdur I., Serra, Llorenç, and Gudmundsson, Vidar

Abstract

We calculate electronic states on a closed cylindrical surface as a model of a core-shell nanowire. The length of the cylinder can be infinite or finite. We define cardinal points on the circumference of the cylinder and consider a spatially uniform magnetic field perpendicular to the cylinder axis, in the direction South-North. The orbital motion of the electrons depends on the radial component of the field which is nonuniform around the circumference: it is equal to the total field at North and South, but vanishes at the West and East sides. For a strong field, when the magnetic length is comparable to the radius of the cylinder, the electronic states at North and South become localized cyclotron orbits, whereas at East and West the states become long and narrow snaking orbits propagating along the cylinder. The energy of the cyclotron states increases with the magnetic field whereas the energy of the snaking states is stable. Consequently, at high magnetic fields the electron density vanishes at North and South and concentrates at East and West. We include spin-orbit interaction with linear Rashba and Dresselhaus models. For a cylinder of finite length the Dresselhaus interaction produces an axial twist of the charge density relative to the center of the wire, which may be amplified in the presence of the Rashba interaction.© EDP Sciences Società Italiana di Fisica Springer-Verlag 2013.

Published
2013

274. Regimes of radiative and nonradiative transitions in transport through an electronic system in a photon cavity reaching a steady state.

Author

Gudmundsson, Vidar, Jonsson, Thorsteinn H., Bernodusson, Maria Laura, Abdullah, Nzar Rauf, Sitek, Anna, Goan, Hsi ‐ Sheng, Tang, Chi ‐ Shung, and Manolescu, Andrei

Subjects
RADIATIVE transitions, FOCK spaces, ELECTRON transport, MARKOVIAN jump linear systems, LINDBLAD resonance
Abstract

We analyze how a multilevel many-electron system in a photon cavity approaches the steady state when coupled to external leads. When a plunger gate is used to lower cavity photon dressed one- and two-electron states below the bias window defined by the external leads, we can identify one regime with nonradiative transitions dominating the electron transport, and another regime with radiative transitions. Both transitions trap the electrons in the states below the bias bringing the system into a steady state. The order of the two regimes and their relative strength depends on the location of the bias window in the energy spectrum of the system and the initial conditions. [ABSTRACT FROM AUTHOR]

Published
2017
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275. Cavity-photon contribution to the effective interaction of electrons in parallel quantum dots.

Author

Gudmundsson, Vidar, Sitek, Anna, Abdullah, Nzar Rauf, Tang, Chi‐Shung, and Manolescu, Andrei

Subjects
QUANTUM dots, PHOTONS, ELECTRON transport, ELECTRON-electron interactions, POLARIZATION (Nuclear physics), ELECTRON delocalization
Abstract

A single cavity photon mode is expected to modify the Coulomb interaction of an electron system in the cavity. Here we investigate this phenomena in a parallel double quantum dot system. We explore properties of the closed system and the system after it has been opened up for electron transport. We show how results for both cases support the idea that the effective electron-electron interaction becomes more repulsive in the presence of a cavity photon field. This can be understood in terms of the cavity photons dressing the polarization terms in the effective mutual electron interaction leading to nontrivial delocalization or polarization of the charge in the double parallel dot potential. In addition, we find that the effective repulsion of the electrons can be reduced by quadrupolar collective oscillations excited by an external classical dipole electric field. [ABSTRACT FROM AUTHOR]

Published
2016
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286. Exploring electronic, optical, and phononic properties of MgX (X= C, N, and O) monolayers using first principle calculations

Author

Abdullah, Nzar Rauf, Abdullah, Botan Jawdat, Azeez, Yousif Hussein, and Gudmundsson, Vidar

Abstract

The electronic, the thermal, and the optical properties of hexagonal MgX monolayers (where X= C, N, and O) are investigated via first principles studies. Ab-initio molecular dynamic, AIMD, simulations using NVT ensembles are performed to check the thermodynamic stability of the monolayers. We find that an MgO monolayer has semiconductor properties with a good thermodynamic stability, while the MgC and the MgN monolayers have metallic characters. The calculated phonon band structures of all the three considered monolayers show no imaginary nonphysical frequencies, thus indicating that they all have excellent dynamic stability. The MgO monolayer has a larger heat capacity then the MgC and the MgN monolayers. The metallic monolayers demonstrate optical response in the IR as a consequence of the metal properties, whereas the semiconducting MgO monolayer demonstrates an active optical response in the near-UV region. The optical response in the near-UV is beneficial for nanoelectronics and photoelectric applications. A semiconducting monolayer is a great choice for thermal management applications since its thermal properties are more attractive than those of the metallic monolayer in terms of heat capacity, which is related to the change in the internal energy of the system.

Published
2023
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