Publications in 2018

1. Nzar Rauf Abdullah, Thorsten Arnold, Chi-Shung Tang, Andrei Manolescu and Vidar Gudmundsson.
Photon-induced tunability of the thermospin current in a Rashba ring.
Journal of Physics: Condensed Matter 30, 145303 (2018).
Abstract The goal of this work is to show how the thermospin polarization current in a quantum ring changes in the presence of Rashba spinorbit coupling and a quantized single photon mode of a cavity the ring is placed in. Employing the reduced density operator and a general master equation formalism, we find that both the Rashba interaction and the photon field can significantly modulate the spin polarization and the thermospin polarization current. Tuning the Rashba coupling constant, degenerate energy levels are formed corresponding to the AharonovCasher destructive phase interference in the quantum ring system. Our analysis indicates that the maximum spin polarization can be observed at the points of degenerate energy levels due to spin accumulation in the system without the photon field. The thermospin current is thus suppressed. In the presence of the cavity, the photon field leads to an additional kinetic momentum of the electron. As a result the spin polarization can be enhanced by the photon field.
URL arXiv BibTeX

@article{0953-8984-30-14-145303 ,
abstract = "The goal of this work is to show how the thermospin polarization current in a quantum ring changes in the presence of Rashba spinorbit coupling and a quantized single photon mode of a cavity the ring is placed in. Employing the reduced density operator and a general master equation formalism, we find that both the Rashba interaction and the photon field can significantly modulate the spin polarization and the thermospin polarization current. Tuning the Rashba coupling constant, degenerate energy levels are formed corresponding to the AharonovCasher destructive phase interference in the quantum ring system. Our analysis indicates that the maximum spin polarization can be observed at the points of degenerate energy levels due to spin accumulation in the system without the photon field. The thermospin current is thus suppressed. In the presence of the cavity, the photon field leads to an additional kinetic momentum of the electron. As a result the spin polarization can be enhanced by the photon field.",
arxiv = "https://arxiv.org/abs/1712.03386",
author = "Nzar Rauf Abdullah and Thorsten Arnold and Chi-Shung Tang and Andrei Manolescu and Vidar Gudmundsson",
journal = "Journal of Physics: Condensed Matter",
number = 14,
pages = 145303,
title = "Photon-induced tunability of the thermospin current in a Rashba ring",
url = "http://stacks.iop.org/0953-8984/30/i=14/a=145303",
volume = 30,
year = 2018
}

2. K Torfason, H V Haraldsson, Á Valfells and A Manolescu.
Molecular dynamics simulations of vacuum diodes.
In 2018 IEEE International Vacuum Electronics Conference (IVEC) (). (2018), 63-64.
BibTeX

@inproceedings{8391553 ,
author = "K. {Torfason} and H. V. {Haraldsson} and Á. {Valfells} and A. {Manolescu}",
booktitle = "2018 IEEE International Vacuum Electronics Conference (IVEC)",
number = "",
pages = "63-64",
title = "Molecular dynamics simulations of vacuum diodes",
volume = "",
year = 2018
}

3. M U Torres, A Sitek, V Gudmundsson and A Manolescu.
Radiated fields by polygonal core-shell nanowires.
In 2018 20th International Conference on Transparent Optical Networks (ICTON) (). (2018), 1-4.
Abstract We calculate the electromagnetic field radiated by tubular nanowires with prismatic geometry and infinite length. The polygonal geometry has implications on the electronic localization; the lowest energy states are localized at the edges of the prism and are separated by a considerable energy gap from the states localized on the facets. This localization can be controlled with external electric or magnetic fields. In particular, by applying a magnetic field transverse to the wire the states may become localized on the lateral regions of the shell, relatively to the direction of the field, leading to channels of opposite currents. Because of the prismatic geometry of the nanowire the current distribution, and hence the radiated electromagnetic field, have an anisotropic structure, which can be modified by the external fields. In this work we study hexagonal, square and triangular nanowires.
arXiv BibTeX

@inproceedings{8473825 ,
abstract = "We calculate the electromagnetic field radiated by tubular nanowires with prismatic geometry and infinite length. The polygonal geometry has implications on the electronic localization; the lowest energy states are localized at the edges of the prism and are separated by a considerable energy gap from the states localized on the facets. This localization can be controlled with external electric or magnetic fields. In particular, by applying a magnetic field transverse to the wire the states may become localized on the lateral regions of the shell, relatively to the direction of the field, leading to channels of opposite currents. Because of the prismatic geometry of the nanowire the current distribution, and hence the radiated electromagnetic field, have an anisotropic structure, which can be modified by the external fields. In this work we study hexagonal, square and triangular nanowires.",
arxiv = "https://arxiv.org/abs/1804.07959",
author = "M. U. {Torres} and A. {Sitek} and V. {Gudmundsson} and A. {Manolescu}",
booktitle = "2018 20th International Conference on Transparent Optical Networks (ICTON)",
number = "",
pages = "1-4",
title = "Radiated fields by polygonal core-shell nanowires",
volume = "",
year = 2018
}

4. K Torfason, A Manolescu and Á Valfells.
Modelling Nano- and Microscale Vacuum Electronics A molecular dynamics approach.
In 2018 IEEE MTT-S International Conference on Numerical Electromagnetic and Multiphysics Modeling and Optimization (NEMO) (). (2018), 1-3.
BibTeX

@inproceedings{8503192 ,
author = "K. {Torfason} and A. {Manolescu} and Á. {Valfells}",
booktitle = "2018 IEEE MTT-S International Conference on Numerical Electromagnetic and Multiphysics Modeling and Optimization (NEMO)",
number = "",
pages = "1-3",
title = "Modelling Nano- and Microscale Vacuum Electronics A molecular dynamics approach",
volume = "",
year = 2018
}

5. K Torfason, A Manolescu and Á Valfells.
High-fidelity Molecular Dynamics of Vacuum Nanoelectronics.
In 2018 31st International Vacuum Nanoelectronics Conference (IVNC) (). (2018), 1-2.
BibTeX

@inproceedings{8520287 ,
author = "K. {Torfason} and A. {Manolescu} and Á. {Valfells}",
booktitle = "2018 31st International Vacuum Nanoelectronics Conference (IVNC)",
number = "",
pages = "1-2",
title = "High-fidelity Molecular Dynamics of Vacuum Nanoelectronics",
volume = "",
year = 2018
}

6. C Palade, A Slav, O Cojocaru, V S Teodorescu, S Lazanu, T Stoica, M T Sultan, H G Svavarsson and M L Ciurea.
Enhanced Photocurrent in GeSi NCs / TiO2Multilayers.
In 2018 International Semiconductor Conference (CAS) (). (2018), 73-76.
BibTeX

@inproceedings{8539740 ,
author = "C. {Palade} and A. {Slav} and O. {Cojocaru} and V. S. {Teodorescu} and S. {Lazanu} and T. {Stoica} and M. T. {Sultan} and H. G. {Svavarsson} and M. L. {Ciurea}",
booktitle = "2018 International Semiconductor Conference (CAS)",
number = "",
pages = "73-76",
title = "Enhanced Photocurrent in GeSi NCs / TiO2Multilayers",
volume = "",
year = 2018
}

7. M T Sultan, J T Gudmundsson, A Manolescu, M L Ciurea and H G Svavarsson.
The Effect of H2/Ar Plasma Treatment Over Photoconductivity of Sige Nanoparticles Sandwiched Between Silicon Oxide Matrix.
In 2018 International Semiconductor Conference (CAS) (). (2018), 257-260.
BibTeX

@inproceedings{8539761 ,
author = "M. T. {Sultan} and J. T. {Gudmundsson} and A. {Manolescu} and M. L. {Ciurea} and H. G. {Svavarsson}",
booktitle = "2018 International Semiconductor Conference (CAS)",
number = "",
pages = "257-260",
title = "The Effect of H2/Ar Plasma Treatment Over Photoconductivity of Sige Nanoparticles Sandwiched Between Silicon Oxide Matrix",
volume = "",
year = 2018
}

8. M T Sultan, J T Gudmundsson, A Manolescu, M L Ciurea, C Palade, A V Maraloiu and H G Svavarsson.
Enhanced Photoconductivity of SIGE-Trilayer Stack by Retrenching Annealing Conditions.
In 2018 International Semiconductor Conference (CAS) (). (2018), 61-64.
BibTeX

@inproceedings{8539775 ,
author = "M. T. {Sultan} and J. T. {Gudmundsson} and A. {Manolescu} and M. L. {Ciurea} and C. {Palade} and A. V. {Maraloiu} and H. G. {Svavarsson}",
booktitle = "2018 International Semiconductor Conference (CAS)",
number = "",
pages = "61-64",
title = "Enhanced Photoconductivity of SIGE-Trilayer Stack by Retrenching Annealing Conditions",
volume = "",
year = 2018
}

9. Nzar Rauf Abdullah, Chi-Shung Tang, Andrei Manolescu and Vidar Gudmundsson.
Spin-dependent heat and thermoelectric currents in a Rashba ring coupled to a photon cavity.
Physica E: Low-dimensional Systems and Nanostructures 95, 102 - 107 (2018).
Abstract Spin-dependent heat and thermoelectric currents in a quantum ring with Rashba spin-orbit interaction placed in a photon cavity are theoretically calculated. The quantum ring is coupled to two external leads with different temperatures. In a resonant regime, with the ring structure in resonance with the photon field, the heat and the thermoelectric currents can be controlled by the Rashba spin-orbit interaction. The heat current is suppressed in the presence of the photon field due to contribution of the two-electron and photon replica states to the transport while the thermoelectric current is not sensitive to changes in parameters of the photon field. Our study opens a possibility to use the proposed interferometric device as a tunable heat current generator in the cavity photon field.
URL arXiv, DOI BibTeX

@article{ABDULLAH2018102 ,
abstract = "Spin-dependent heat and thermoelectric currents in a quantum ring with Rashba spin-orbit interaction placed in a photon cavity are theoretically calculated. The quantum ring is coupled to two external leads with different temperatures. In a resonant regime, with the ring structure in resonance with the photon field, the heat and the thermoelectric currents can be controlled by the Rashba spin-orbit interaction. The heat current is suppressed in the presence of the photon field due to contribution of the two-electron and photon replica states to the transport while the thermoelectric current is not sensitive to changes in parameters of the photon field. Our study opens a possibility to use the proposed interferometric device as a tunable heat current generator in the cavity photon field.",
arxiv = "https://arxiv.org/abs/1707.08416",
author = "Nzar Rauf Abdullah and Chi-Shung Tang and Andrei Manolescu and Vidar Gudmundsson",
doi = "https://doi.org/10.1016/j.physe.2017.09.011",
issn = "1386-9477",
journal = "Physica E: Low-dimensional Systems and Nanostructures",
keywords = "Thermo-optic effects, Electronic transport in mesoscopic systems, Cavity quantum electrodynamics, Electro-optical effects",
pages = "102 - 107",
title = "Spin-dependent heat and thermoelectric currents in a Rashba ring coupled to a photon cavity",
url = "http://www.sciencedirect.com/science/article/pii/S1386947717311372",
volume = 95,
year = 2018
}

10. Nzar Rauf Abdullah, Chi-Shung Tang, Andrei Manolescu and Vidar Gudmundsson.
Effects of photon field on heat transport through a quantum wire attached to leads.
Physics Letters A 382, 199 - 204 (2018).
Abstract We theoretically investigate photo-thermoelectric transport through a quantum wire in a photon cavity coupled to electron reservoirs with different temperatures. Our approach, based on a quantum master equation, allows us to investigate the influence of a quantized photon field on the heat current and thermoelectric transport in the system. We find that the heat current through the quantum wire is influenced by the photon field resulting in a negative heat current in certain cases. The characteristics of the transport are studied by tuning the ratio, h??/kB?T, between the photon energy, h??, and the thermal energy, kB?T. The thermoelectric transport is enhanced by the cavity photons when kB?T>h??. By contrast, if kB?T
URL arXiv, DOI BibTeX

@article{ABDULLAH2018199 ,
abstract = "We theoretically investigate photo-thermoelectric transport through a quantum wire in a photon cavity coupled to electron reservoirs with different temperatures. Our approach, based on a quantum master equation, allows us to investigate the influence of a quantized photon field on the heat current and thermoelectric transport in the system. We find that the heat current through the quantum wire is influenced by the photon field resulting in a negative heat current in certain cases. The characteristics of the transport are studied by tuning the ratio, h??/kB?T, between the photon energy, h??, and the thermal energy, kB?T. The thermoelectric transport is enhanced by the cavity photons when kB?T>h??. By contrast, if kB?T
11. Nzar Rauf Abdullah, Thorsten Arnold, Chi-Shung Tang, Andrei Manolescu and Vidar Gudmundsson.
Photon-induced tunability of the thermospin current in a Rashba ring.
Journal of Physics: Condensed Matter 30, 145303 (March 2018).
Abstract The goal of this work is to show how the thermospin polarization current in a quantum ring changes in the presence of Rashba spin–orbit coupling and a quantized single photon mode of a cavity the ring is placed in. Employing the reduced density operator and a general master equation formalism, we find that both the Rashba interaction and the photon field can significantly modulate the spin polarization and the thermospin polarization current. Tuning the Rashba coupling constant, degenerate energy levels are formed corresponding to the Aharonov–Casher destructive phase interference in the quantum ring system. Our analysis indicates that the maximum spin polarization can be observed at the points of degenerate energy levels due to spin accumulation in the system without the photon field. The thermospin current is thus suppressed. In the presence of the cavity, the photon field leads to an additional kinetic momentum of the electron. As a result the spin polarization can be enhanced by the photon field.
URL, DOI BibTeX

@article{Abdullah_2018 ,
abstract = "The goal of this work is to show how the thermospin polarization current in a quantum ring changes in the presence of Rashba spin–orbit coupling and a quantized single photon mode of a cavity the ring is placed in. Employing the reduced density operator and a general master equation formalism, we find that both the Rashba interaction and the photon field can significantly modulate the spin polarization and the thermospin polarization current. Tuning the Rashba coupling constant, degenerate energy levels are formed corresponding to the Aharonov–Casher destructive phase interference in the quantum ring system. Our analysis indicates that the maximum spin polarization can be observed at the points of degenerate energy levels due to spin accumulation in the system without the photon field. The thermospin current is thus suppressed. In the presence of the cavity, the photon field leads to an additional kinetic momentum of the electron. As a result the spin polarization can be enhanced by the photon field.",
author = "Nzar Rauf Abdullah and Thorsten Arnold and Chi-Shung Tang and Andrei Manolescu and Vidar Gudmundsson",
doi = "10.1088/1361-648x/aab255",
journal = "Journal of Physics: Condensed Matter",
month = "mar",
number = 14,
pages = 145303,
publisher = "{IOP} Publishing",
title = "Photon-induced tunability of the thermospin current in a Rashba ring",
url = "https://doi.org/10.1088%2F1361-648x%2Faab255",
volume = 30,
year = 2018
}

12. Vidar Gudmundsson, Nzar Rauf Abdulla, Anna Sitek, Hsi-Sheng Goan, Chi-Shung Tang and Andrei Manolescu.
Electroluminescence Caused by the Transport of Interacting Electrons through Parallel Quantum Dots in a Photon Cavity.
Annalen der Physik 530, 1700334 (2018).
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.
URL, DOI BibTeX

@article{doi:10.1002/andp.201700334 ,
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.",
author = "Gudmundsson, Vidar and Abdulla, Nzar Rauf and Sitek, Anna and Goan, Hsi-Sheng and Tang, Chi-Shung and Manolescu, Andrei",
doi = "10.1002/andp.201700334",
eprint = "https://onlinelibrary.wiley.com/doi/pdf/10.1002/andp.201700334",
journal = "Annalen der Physik",
keywords = "configuration interactions, electroluminescence, electron transport, photon cavity, photon correlations",
number = 2,
pages = 1700334,
title = "Electroluminescence Caused by the Transport of Interacting Electrons through Parallel Quantum Dots in a Photon Cavity",
url = "https://onlinelibrary.wiley.com/doi/abs/10.1002/andp.201700334",
volume = 530,
year = 2018
}

13. Anna Sitek, Miguel Urbaneja Torres, Kristinn Torfason, Vidar Gudmundsson, Andrea Bertoni and Andrei Manolescu.
Excitons in Core-Shell Nanowires with Polygonal Cross Sections.
Nano Letters 18, 2581-2589 (2018).
Abstract The distinctive prismatic geometry of semiconductor coreshell nanowires leads to complex localization patterns of carriers. Here, we describe the formation of optically active in-gap excitonic states induced by the interplay between localization of carriers in the corners and their mutual Coulomb interaction. To compute the energy spectra and configurations of excitons created in the conductive shell, we use a multielectron numerical approach based on the exact solution of the multiparticle Hamiltonian for electrons in the valence and conduction bands, which includes the Coulomb interaction in a nonperturbative manner. We expose the formation of well-separated quasidegenerate levels, and focus on the implications of the electron localization in the corners or on the sides of triangular, square, and hexagonal cross sections. We obtain excitonic in-gap states associated with symmetrically distributed electrons in the spin singlet configuration. They acquire large contributions due to Coulomb interaction, and thus are shifted to much higher energies than other states corresponding to the conduction electron and the vacancy localized in the same corner. We compare the results of the multielectron method with those of an electronhole model, and we show that the latter does not reproduce the singlet excitonic states. We also obtain the exciton lifetime and explain selection rules which govern the recombination process.
URL arXiv, DOI BibTeX

@article{doi:10.1021/acs.nanolett.8b00309 ,
abstract = "The distinctive prismatic geometry of semiconductor coreshell nanowires leads to complex localization patterns of carriers. Here, we describe the formation of optically active in-gap excitonic states induced by the interplay between localization of carriers in the corners and their mutual Coulomb interaction. To compute the energy spectra and configurations of excitons created in the conductive shell, we use a multielectron numerical approach based on the exact solution of the multiparticle Hamiltonian for electrons in the valence and conduction bands, which includes the Coulomb interaction in a nonperturbative manner. We expose the formation of well-separated quasidegenerate levels, and focus on the implications of the electron localization in the corners or on the sides of triangular, square, and hexagonal cross sections. We obtain excitonic in-gap states associated with symmetrically distributed electrons in the spin singlet configuration. They acquire large contributions due to Coulomb interaction, and thus are shifted to much higher energies than other states corresponding to the conduction electron and the vacancy localized in the same corner. We compare the results of the multielectron method with those of an electronhole model, and we show that the latter does not reproduce the singlet excitonic states. We also obtain the exciton lifetime and explain selection rules which govern the recombination process.",
arxiv = "https://hdl.handle.net/20.500.11815/694",
author = "Sitek, Anna and Urbaneja Torres, Miguel and Torfason, Kristinn and Gudmundsson, Vidar and Bertoni, Andrea and Manolescu, Andrei",
doi = "10.1021/acs.nanolett.8b00309",
eprint = "https://doi.org/10.1021/acs.nanolett.8b00309",
journal = "Nano Letters",
note = "PMID: 29578727",
number = 4,
pages = "2581-2589",
title = "Excitons in Core-Shell Nanowires with Polygonal Cross Sections",
url = "https://doi.org/10.1021/acs.nanolett.8b00309",
volume = 18,
year = 2018
}

14. Halldor G Svavarsson, Johannes E Valberg, Hronn Arnardottir and Asa Brynjolfsdottir.
Carbon dioxide from geothermal gas converted to biomass by cultivating coccoid cyanobacteria.
Environmental Technology 39, 2097-2104 (2018).
Abstract ABSTRACTThe Blue Lagoon is a geothermal aquifer with a diverse ecosystem located within the Reykjanes UNESCO Global Geopark on Iceland’s Reykjanes Peninsula. Blue Lagoon Ltd., which exploits the aquifer, isolated a strain of coccoid cyanobacteria Cyanobacterium aponinum (C. aponinum) from the geothermal fluid of the Blue Lagoon more than two decades ago. Since then Blue Lagoon Ltd. has cultivated it in a photobioreactor, for use as an active ingredient in its skin care products. Until recently, the cultivation of C. aponinum was achieved by feeding it on 99.99% (4N) bottled carbon dioxide (CO2). In this investigation, C. aponinum was cultivated using unmodified, non-condensable geothermal gas (geogas) emitted from a nearby geothermal powerplant as the feed-gas instead of the 4N-gas. The geogas contains roughly 90% vol CO2 and 2% vol hydrogen sulfide (H2S). A comparison of both CO2 sources was made. It was observed that the use of geogas did enhance the conversion efficiency. A 13 weeks’ average CO2 conversion efficiency of C. aponinum was 43% and 31% when fed on geogas and 4N-gas, respectively. Despite the high H2S concentration in the geogas, sulfur accumulation in the cultivated biomass was similar for both gas sources. Our results provide a model of a CO2 sequestration by photosynthetic conversion of otherwise unused geothermal emission gas into biomass.
URL, DOI BibTeX

@article{doi:10.1080/09593330.2017.1349840 ,
abstract = "ABSTRACTThe Blue Lagoon is a geothermal aquifer with a diverse ecosystem located within the Reykjanes UNESCO Global Geopark on Iceland’s Reykjanes Peninsula. Blue Lagoon Ltd., which exploits the aquifer, isolated a strain of coccoid cyanobacteria Cyanobacterium aponinum (C. aponinum) from the geothermal fluid of the Blue Lagoon more than two decades ago. Since then Blue Lagoon Ltd. has cultivated it in a photobioreactor, for use as an active ingredient in its skin care products. Until recently, the cultivation of C. aponinum was achieved by feeding it on 99.99\% (4N) bottled carbon dioxide (CO2). In this investigation, C. aponinum was cultivated using unmodified, non-condensable geothermal gas (geogas) emitted from a nearby geothermal powerplant as the feed-gas instead of the 4N-gas. The geogas contains roughly 90\% vol CO2 and 2\% vol hydrogen sulfide (H2S). A comparison of both CO2 sources was made. It was observed that the use of geogas did enhance the conversion efficiency. A 13 weeks’ average CO2 conversion efficiency of C. aponinum was 43\% and 31\% when fed on geogas and 4N-gas, respectively. Despite the high H2S concentration in the geogas, sulfur accumulation in the cultivated biomass was similar for both gas sources. Our results provide a model of a CO2 sequestration by photosynthetic conversion of otherwise unused geothermal emission gas into biomass.",
author = "Halldor G. Svavarsson and Johannes E. Valberg and Hronn Arnardottir and Asa Brynjolfsdottir",
doi = "10.1080/09593330.2017.1349840",
eprint = "https://doi.org/10.1080/09593330.2017.1349840",
journal = "Environmental Technology",
note = "PMID: 28662603",
number = 16,
pages = "2097-2104",
publisher = "Taylor & Francis",
title = "Carbon dioxide from geothermal gas converted to biomass by cultivating coccoid cyanobacteria",
url = "https://doi.org/10.1080/09593330.2017.1349840",
volume = 39,
year = 2018
}

15. Sigurdur I Erlingsson, Jens H Bardarson and Andrei Manolescu.
Thermoelectric current in topological insulator nanowires with impurities.
Beilstein journal of nanotechnology 9, 1156 (2018).
Abstract In this paper we consider charge current generated by maintaining a temperature difference over a nanowire at zero voltage bias. For topological insulator nanowires in a perpendicular magnetic field the current can change sign as the temperature of one end is increased. Here we study how this thermoelectric current sign reversal depends on the magnetic field and how impurities affect the size of the thermoelectric current. We consider both scalar and magnetic impurities and show that their influence on the current are quite similar, although the magnetic impurities seem to be more effective in reducing the effect. For moderate impurity concentration the sign reversal persists.
arXiv BibTeX

@article{erlingsson2018thermoelectric ,
abstract = "In this paper we consider charge current generated by maintaining a temperature difference over a nanowire at zero voltage bias. For topological insulator nanowires in a perpendicular magnetic field the current can change sign as the temperature of one end is increased. Here we study how this thermoelectric current sign reversal depends on the magnetic field and how impurities affect the size of the thermoelectric current. We consider both scalar and magnetic impurities and show that their influence on the current are quite similar, although the magnetic impurities seem to be more effective in reducing the effect. For moderate impurity concentration the sign reversal persists.",
arxiv = "https://arxiv.org/abs/1803.04507",
author = "Erlingsson, Sigurdur I and Bardarson, Jens H and Manolescu, Andrei",
journal = "Beilstein journal of nanotechnology",
pages = 1156,
publisher = "Beilstein-Institut",
title = "Thermoelectric current in topological insulator nanowires with impurities",
volume = 9,
year = 2018
}

16. Vidar Gudmundsson, Nzar Rauf Abdullah, Anna Sitek, Hsi-Sheng Goan, Chi-Shung Tang and Andrei Manolescu.
Current correlations for the transport of interacting electrons through parallel quantum dots in a photon cavity.
Physics Letters A 382, 1672 - 1678 (2018).
Abstract We calculate the current correlations for the steady-state electron transport through multi-level parallel quantum dots embedded in a short quantum wire, that is placed in a non-perfect photon cavity. We account for the electron–electron Coulomb interaction, and the para- and diamagnetic electron–photon interactions with a stepwise scheme of configuration interactions and truncation of the many-body Fock spaces. In the spectral density of the temporal current–current correlations we identify all the transitions, radiative and non-radiative, active in the system in order to maintain the steady state. We observe strong signs of two types of Rabi oscillations.
URL arXiv, DOI BibTeX

@article{GUDMUNDSSON20181672 ,
abstract = "We calculate the current correlations for the steady-state electron transport through multi-level parallel quantum dots embedded in a short quantum wire, that is placed in a non-perfect photon cavity. We account for the electron–electron Coulomb interaction, and the para- and diamagnetic electron–photon interactions with a stepwise scheme of configuration interactions and truncation of the many-body Fock spaces. In the spectral density of the temporal current–current correlations we identify all the transitions, radiative and non-radiative, active in the system in order to maintain the steady state. We observe strong signs of two types of Rabi oscillations.",
arxiv = "https://arxiv.org/abs/1707.08295",
author = "Vidar Gudmundsson and Nzar Rauf Abdullah and Anna Sitek and Hsi-Sheng Goan and Chi-Shung Tang and Andrei Manolescu",
doi = "https://doi.org/10.1016/j.physleta.2018.04.017",
issn = "0375-9601",
journal = "Physics Letters A",
keywords = "Current correlations, Electronic transport in mesoscopic systems, Cavity quantum electrodynamics, Electro-optical effects",
number = 25,
pages = "1672 - 1678",
title = "Current correlations for the transport of interacting electrons through parallel quantum dots in a photon cavity",
url = "http://www.sciencedirect.com/science/article/pii/S0375960118303748",
volume = 382,
year = 2018
}

17. Sigurdur I Erlingsson and José Carlos Egues.
Shubnikov-de Haas oscillations revisited.
In International School and Conference on Physics and Applications of Spin Phenomena in Solids - PASPS. (2018).
BibTeX

@inproceedings{inproceedings8ac5e0d9 ,
author = "Erlingsson, Sigurdur I. and Egues, José Carlos",
booktitle = "International School and Conference on Physics and Applications of Spin Phenomena in Solids - PASPS",
publisher = "Johannes Kepler University Linz - JKU",
title = "Shubnikov-de Haas oscillations revisited",
year = 2018
}

18. G A Nemnes, T L Mitran, A Manolescu and Daniela Dragoman.
Electric field effect in boron and nitrogen doped graphene bilayers.
Computational Materials Science 155, 175 - 179 (2018).
Abstract Unlike single layer graphene, in the case of AB-stacked bilayer graphene (BLG) one can induce a non-zero energy gap by breaking the inversion symmetry between the two layers using a perpendicular electric field. This is an essential requirement in field-effect applications, particularly since the induced gap in BLG systems can be further tuned by the magnitude of the external electric field. Doping is another way to modify the electronic properties of graphene based systems. We investigate here BLG systems doped with boron and nitrogen in the presence of external electric field, in the framework of density functional theory (DFT) calculations. Highly doped BLG systems are known to behave as degenerate semiconductors, where the Fermi energy depends on the doping concentration but, in addition, we show that the electronic properties drastically depend also on the applied electric field. By changing the magnitude and the orientation of the electric field, the gap size and position relative to the Fermi level may be tuned, essentially controlling the effect of the extrinsic doping. In this context, we discuss in how far the external electric field may suitably adjust the effective doping and, implicitly, the conduction properties of doped BLG systems.
URL, DOI BibTeX

@article{NEMNES2018175 ,
abstract = "Unlike single layer graphene, in the case of AB-stacked bilayer graphene (BLG) one can induce a non-zero energy gap by breaking the inversion symmetry between the two layers using a perpendicular electric field. This is an essential requirement in field-effect applications, particularly since the induced gap in BLG systems can be further tuned by the magnitude of the external electric field. Doping is another way to modify the electronic properties of graphene based systems. We investigate here BLG systems doped with boron and nitrogen in the presence of external electric field, in the framework of density functional theory (DFT) calculations. Highly doped BLG systems are known to behave as degenerate semiconductors, where the Fermi energy depends on the doping concentration but, in addition, we show that the electronic properties drastically depend also on the applied electric field. By changing the magnitude and the orientation of the electric field, the gap size and position relative to the Fermi level may be tuned, essentially controlling the effect of the extrinsic doping. In this context, we discuss in how far the external electric field may suitably adjust the effective doping and, implicitly, the conduction properties of doped BLG systems.",
author = "G.A. Nemnes and T.L. Mitran and A. Manolescu and Daniela Dragoman",
doi = "https://doi.org/10.1016/j.commatsci.2018.08.054",
issn = "0927-0256",
journal = "Computational Materials Science",
keywords = "Graphene bilayer, Field effect, Effective doping",
pages = "175 - 179",
title = "Electric field effect in boron and nitrogen doped graphene bilayers",
url = "http://www.sciencedirect.com/science/article/pii/S0927025618305822",
volume = 155,
year = 2018
}

19. George Alexandru Nemnes, Cristina Besleaga, Andrei Gabriel Tomulescu, Alexandra Palici, Lucian Pintilie, Andrei Manolescu and Ioana Pintilie.
How measurement protocols influence the dynamic J-V characteristics of perovskite solar cells: Theory and experiment.
Solar Energy 173, 976 - 983 (2018).
Abstract The dynamic effects observed in the J-V measurements represent one important hallmark in the behavior of the perovskite solar cells. Proper measurement protocols (MPs) should be employed for the experimental data reproducibility, in particular for a reliable evaluation of the power conversion efficiency (PCE), as well as for a meaningful characterization of the type and magnitude of the hysteresis. We discuss here several MPs by comparing the experimental J-V characteristics with simulated ones using the dynamic electrical model (DEM). Pre-poling conditions and bias scan rate can have a dramatic influence not only on the apparent solar cell performance, but also on the hysteretic phenomena. Under certain measurement conditions, a hysteresis-free behavior with relatively high PCEs may be observed, although the J-V characteristics may be far away from the stationary case. Furthermore, forward-reverse and reverse-forward bias scans show qualitatively different behaviors regarding the type of the hysteresis, normal and inverted, depending on the bias pre-poling. We emphasize here that correlated double-scans, forward-reverse or reverse-forward, where the second scan is conducted in the opposite sweep direction and begins immediately after the first scan is complete, are essential for a correct assessment of the dynamic hysteresis. In this context, we define a hysteresis index which consistently assigns the hysteresis type and magnitude. Our DEM simulations, supported by experimental data, provide further guidance for an efficient and accurate determination of the stationary J-V characteristics, showing that the type and magnitude of the dynamic hysteresis may be affected by unintentional pre-conditioning in typical experiments.
URL arXiv, DOI BibTeX

@article{NEMNES2018976 ,
abstract = "The dynamic effects observed in the J-V measurements represent one important hallmark in the behavior of the perovskite solar cells. Proper measurement protocols (MPs) should be employed for the experimental data reproducibility, in particular for a reliable evaluation of the power conversion efficiency (PCE), as well as for a meaningful characterization of the type and magnitude of the hysteresis. We discuss here several MPs by comparing the experimental J-V characteristics with simulated ones using the dynamic electrical model (DEM). Pre-poling conditions and bias scan rate can have a dramatic influence not only on the apparent solar cell performance, but also on the hysteretic phenomena. Under certain measurement conditions, a hysteresis-free behavior with relatively high PCEs may be observed, although the J-V characteristics may be far away from the stationary case. Furthermore, forward-reverse and reverse-forward bias scans show qualitatively different behaviors regarding the type of the hysteresis, normal and inverted, depending on the bias pre-poling. We emphasize here that correlated double-scans, forward-reverse or reverse-forward, where the second scan is conducted in the opposite sweep direction and begins immediately after the first scan is complete, are essential for a correct assessment of the dynamic hysteresis. In this context, we define a hysteresis index which consistently assigns the hysteresis type and magnitude. Our DEM simulations, supported by experimental data, provide further guidance for an efficient and accurate determination of the stationary J-V characteristics, showing that the type and magnitude of the dynamic hysteresis may be affected by unintentional pre-conditioning in typical experiments.",
arxiv = "https://arxiv.org/abs/1803.00285",
author = "George Alexandru Nemnes and Cristina Besleaga and Andrei Gabriel Tomulescu and Alexandra Palici and Lucian Pintilie and Andrei Manolescu and Ioana Pintilie",
doi = "https://doi.org/10.1016/j.solener.2018.08.033",
issn = "0038-092X",
journal = "Solar Energy",
keywords = "Measurement protocol, Perovskite solar cell, Hysteresis type, Hysteresis index",
pages = "976 - 983",
title = "How measurement protocols influence the dynamic J-V characteristics of perovskite solar cells: Theory and experiment",
url = "http://www.sciencedirect.com/science/article/pii/S0038092X1830803X",
volume = 173,
year = 2018
}

20. Miguel Urbaneja Torres, Anna Sitek, Sigurdur I Erlingsson, Gunnar Thorgilsson, Vidar Gudmundsson and Andrei Manolescu.
Conductance features of core-shell nanowires determined by their internal geometry.
Phys. Rev. B 98, 085419 (August 2018).
URL, DOI BibTeX

@article{PhysRevB.98.085419 ,
author = "Urbaneja Torres, Miguel and Sitek, Anna and Erlingsson, Sigurdur I. and Thorgilsson, Gunnar and Gudmundsson, Vidar and Manolescu, Andrei",
doi = "10.1103/PhysRevB.98.085419",
issue = 8,
journal = "Phys. Rev. B",
month = "Aug",
numpages = 10,
pages = 085419,
publisher = "American Physical Society",
title = "Conductance features of core-shell nanowires determined by their internal geometry",
volume = 98,
year = 2018
}

21. Simon Wozny, Karel Vyborny, Wolfgang Belzig and Sigurdur I Erlingsson.
Gap formation in helical edge states with magnetic impurities.
Phys. Rev. B 98, 165423 (October 2018).
URL, DOI BibTeX

@article{PhysRevB.98.165423 ,
author = "Wozny, Simon and Vyborny, Karel and Belzig, Wolfgang and Erlingsson, Sigurdur I.",
doi = "10.1103/PhysRevB.98.165423",
issue = 16,
journal = "Phys. Rev. B",
month = "Oct",
numpages = 6,
pages = 165423,
publisher = "American Physical Society",
title = "Gap formation in helical edge states with magnetic impurities",
volume = 98,
year = 2018
}

22. Alexandra Palici, George Alexandru Nemnes, Cristina Besleaga, Lucian Pintilie, Dragos-Victor Anghel, Ioana Pintilie and Andrei Manolescu.
The Influence of the Relaxation Time on the Dynamic Hysteresis in Perovskite Solar Cells.
EPJ Web Conf. 173, 03017 (2018).
URL, DOI BibTeX

@article{refId0 ,
author = "{Palici, Alexandra} and {Nemnes, George Alexandru} and {Besleaga, Cristina} and {Pintilie, Lucian} and {Anghel, Dragos-Victor} and {Pintilie, Ioana} and {Manolescu, Andrei}",
doi = "10.1051/epjconf/201817303017",
journal = "EPJ Web Conf.",
pages = 03017,
title = "The Influence of the Relaxation Time on the Dynamic Hysteresis in Perovskite Solar Cells",
url = "https://doi.org/10.1051/epjconf/201817303017",
volume = 173,
year = 2018
}

23. Tudor D Stanescu, Anna Sitek and Andrei Manolescu.
Robust topological phase in proximitized core–shell nanowires coupled to multiple superconductors.
Beilstein Journal of Nanotechnology 9, 1512-1526 (2018).
Abstract We consider core-shell nanowires with prismatic geometry contacted with two or more superconductors in the presence of a magnetic field applied parallel to the wire. In this geometry, the lowest energy states are localized on the outer edges of the shell, which strongly inhibits the orbital effects of the longitudinal magnetic field that are detrimental to Majorana physics. Using a tight-binding model of coupled parallel chains, we calculate the topological phase diagram of the hybrid system in the presence of non-vanishing transverse potentials and finite relative phases between the parent superconductors. We show that having finite relative phases strongly enhances the stability of the induced topological superconductivity over a significant range of chemical potentials and reduces the value of the critical field associated with the topological quantum phase transition.
arXiv, DOI BibTeX

@article{Stanescu2018 ,
abstract = "We consider core-shell nanowires with prismatic geometry contacted with two or more superconductors in the presence of a magnetic field applied parallel to the wire. In this geometry, the lowest energy states are localized on the outer edges of the shell, which strongly inhibits the orbital effects of the longitudinal magnetic field that are detrimental to Majorana physics. Using a tight-binding model of coupled parallel chains, we calculate the topological phase diagram of the hybrid system in the presence of non-vanishing transverse potentials and finite relative phases between the parent superconductors. We show that having finite relative phases strongly enhances the stability of the induced topological superconductivity over a significant range of chemical potentials and reduces the value of the critical field associated with the topological quantum phase transition.",
arxiv = "https://arxiv.org/abs/1804.05446",
author = "Tudor D. Stanescu and Anna Sitek and Andrei Manolescu",
doi = "10.3762/bjnano.9.142",
issn = "2190-4286",
journal = "Beilstein Journal of Nanotechnology",
pages = "1512-1526",
title = "Robust topological phase in proximitized core–shell nanowires coupled to multiple superconductors",
volume = 9,
year = 2018
}

24. Miguel Urbaneja Torres, Anna Sitek, Vidar Gudmundsson and Andrei Manolescu.
Radiated fields by polygonal core-shell nanowires.
arXiv preprint arXiv:1804.07959 (2018).
Abstract We calculate the electromagnetic field radiated by tubular nanowires with prismatic geometry and infinite length. The polygonal geometry has implications on the electronic localization; the lowest energy states are localized at the edges of the prism and are separated by a considerable energy gap from the states localized on the facets. This localization can be controlled with external electric or magnetic fields. In particular, by applying a magnetic field transverse to the wire the states may become localized on the lateral regions of the shell, relatively to the direction of the field, leading to channels of opposite currents. Because of the prismatic geometry of the nanowire the current distribution, and hence the radiated electromagnetic field, have an anisotropic structure, which can be modified by the external fields. In this work we study hexagonal, square and triangular nanowires.
arXiv BibTeX

@article{torres2018radiated ,
abstract = "We calculate the electromagnetic field radiated by tubular nanowires with prismatic geometry and infinite length. The polygonal geometry has implications on the electronic localization; the lowest energy states are localized at the edges of the prism and are separated by a considerable energy gap from the states localized on the facets. This localization can be controlled with external electric or magnetic fields. In particular, by applying a magnetic field transverse to the wire the states may become localized on the lateral regions of the shell, relatively to the direction of the field, leading to channels of opposite currents. Because of the prismatic geometry of the nanowire the current distribution, and hence the radiated electromagnetic field, have an anisotropic structure, which can be modified by the external fields. In this work we study hexagonal, square and triangular nanowires.",
arxiv = "https://arxiv.org/abs/1804.07959",
author = "Torres, Miguel Urbaneja and Sitek, Anna and Gudmundsson, Vidar and Manolescu, Andrei",
journal = "arXiv preprint arXiv:1804.07959",
title = "Radiated fields by polygonal core-shell nanowires",
year = 2018
}