M Ilkov, K Torfason, A Manolescu and A Valfells.

**Synchronization in Arrays of Vacuum Microdiodes**.*Electron Devices, IEEE Transactions on*PP, 1-1 (2014).

Abstract Simulations have shown that space-charge effects can lead to regular modulation of photoemitted beams in vacuum diodes with gap sizes on the order of 1 μm and accelerating voltage on the order of $1$ V. These modulations are in the terahertz regime and can be tuned by simply changing the emitter area or accelerating vacuum field. The average current in the diode corresponds to the Child–Langmuir current, but the amplitude of the oscillations is affected by various factors. Given the small size and voltage of the system, the maximum radiated ac power is expected to be small. In this paper, we show that an array of small emitters produces higher frequency signals than a single large emitter of the same area and how these emitters may be synchronized to produce higher power signals.

arXiv, DOI BibTeX@article{6979259, author = "Ilkov, M. and Torfason, K. and Manolescu, A. and Valfells, A.", journal = "Electron Devices, IEEE Transactions on", title = "Synchronization in Arrays of Vacuum Microdiodes", year = 2014, month = "", volume = "PP", number = 99, pages = "1-1", abstract = "Simulations have shown that space-charge effects can lead to regular modulation of photoemitted beams in vacuum diodes with gap sizes on the order of 1 μm and accelerating voltage on the order of $1$ V. These modulations are in the terahertz regime and can be tuned by simply changing the emitter area or accelerating vacuum field. The average current in the diode corresponds to the Child--Langmuir current, but the amplitude of the oscillations is affected by various factors. Given the small size and voltage of the system, the maximum radiated ac power is expected to be small. In this paper, we show that an array of small emitters produces higher frequency signals than a single large emitter of the same area and how these emitters may be synchronized to produce higher power signals.", keywords = "Cathodes;Couplings;Frequency synchronization;Oscillators;Quantum cascade lasers;Space charge;Synchronization;Synchronization;terahertz;vacuum microelectronics.", doi = "10.1109/TED.2014.2370680", issn = "0018-9383", arxiv = "http://arxiv.org/abs/1409.0516" }

Tomas Orn Rosdahl, Andrei Manolescu and Vidar Gudmundsson.

**Signature of Snaking States in the Conductance of Core–Shell Nanowires**.*Nano Letters*(2014).

Abstract We model a core–shell nanowire (CSN) by a cylindrical surface of finite length. A uniform magnetic field perpendicular to the axis of the cylinder forms electron states along the lines of zero radial field projection, which can classically be described as snaking states. In a strong field, these states converge pairwise to quasidegenerate levels, which are situated at the bottom of the energy spectrum. We calculate the conductance of the CSN by coupling it to leads and predict that the snaking states govern transport at low chemical potential, forming isolated peaks, each of which may be split in two by applying a transverse electric field. If the contacts with the leads do not completely surround the CSN, as is usually the case in experiments, the amplitude of the snaking peaks changes when the magnetic field is rotated, determined by the overlap of the contacts with the snaking states.

URL arXiv, DOI BibTeX@article{doi:10.1021/nl503499w, author = "Rosdahl, Tomas Orn and Manolescu, Andrei and Gudmundsson, Vidar", title = "Signature of Snaking States in the Conductance of Core–Shell Nanowires", journal = "Nano Letters", year = 2014, doi = "10.1021/nl503499w", note = "PMID: 25426964", url = "http://dx.doi.org/10.1021/nl503499w", arxiv = "http://arxiv.org/abs/1409.3429", eprint = "http://dx.doi.org/10.1021/nl503499w", abstract = "We model a core–shell nanowire (CSN) by a cylindrical surface of finite length. A uniform magnetic field perpendicular to the axis of the cylinder forms electron states along the lines of zero radial field projection, which can classically be described as snaking states. In a strong field, these states converge pairwise to quasidegenerate levels, which are situated at the bottom of the energy spectrum. We calculate the conductance of the CSN by coupling it to leads and predict that the snaking states govern transport at low chemical potential, forming isolated peaks, each of which may be split in two by applying a transverse electric field. If the contacts with the leads do not completely surround the CSN, as is usually the case in experiments, the amplitude of the snaking peaks changes when the magnetic field is rotated, determined by the overlap of the contacts with the snaking states." }

Anda Elena Stanciu, George Alexandru Nemnes and Andrei Manolescu.

**Thermoelectric effects in nanostructured quantum wires in the non-linear temperature regime**.*arXiv preprint arXiv:1411.6018*(2014).

Abstract The thermoelectric voltage of a quantum dot connected to leads is calculated using the scattering R-matrix method. Our approach takes into account a temperature gradient between the contacts beyond the linear regime. We obtain sign changes of the thermopower when varying the temperature or the chemical potential around the resonances. The influence of the coupling strength of the contacts and of the thermoelectric field on the thermoelectric voltage is discussed.

arXiv BibTeX@article{stanciu2014thermoelectric, title = "Thermoelectric effects in nanostructured quantum wires in the non-linear temperature regime", author = "Stanciu, Anda Elena and Nemnes, George Alexandru and Manolescu, Andrei", journal = "arXiv preprint arXiv:1411.6018", arxiv = "http://arxiv.org/abs/1411.6018", year = 2014, abstract = "The thermoelectric voltage of a quantum dot connected to leads is calculated using the scattering R-matrix method. Our approach takes into account a temperature gradient between the contacts beyond the linear regime. We obtain sign changes of the thermopower when varying the temperature or the chemical potential around the resonances. The influence of the coupling strength of the contacts and of the thermoelectric field on the thermoelectric voltage is discussed." }

Andreea A Nila, George Alexandru Nemnes and Andrei Manolescu.

**Ab initio investigation of optical properties in triangular graphene-boron nitride core-shell nanostructures**.*arXiv preprint arXiv:1411.6042*(2014).

Abstract We calculate the optical properties of atomic-sized core-shell graphene - boron nitride nanoflakes with triangular shaped crossection using the density functional theory. The optical properties can be tuned by using different sizes and proportions of the core-shell materials. Anisotropic effects manifested in the absorption of unpolarized light with different orientations of the optical vector are pointed out.

arXiv BibTeX@article{nila2014ab, title = "Ab initio investigation of optical properties in triangular graphene-boron nitride core-shell nanostructures", author = "Nila, Andreea A and Nemnes, George Alexandru and Manolescu, Andrei", journal = "arXiv preprint arXiv:1411.6042", arxiv = "http://arxiv.org/abs/1411.6042", year = 2014, abstract = "We calculate the optical properties of atomic-sized core-shell graphene - boron nitride nanoflakes with triangular shaped crossection using the density functional theory. The optical properties can be tuned by using different sizes and proportions of the core-shell materials. Anisotropic effects manifested in the absorption of unpolarized light with different orientations of the optical vector are pointed out." }

Nzar Rauf Abdullah, Chi-Shung Tang, Andrei Manolescu and Vidar Gudmundsson.

**Cavity-photon-switched coherent transient transport in a double quantum waveguide**.*Journal of Applied Physics*116, - (2014).

Abstract We study a cavity-photon-switched coherent electron transport in a symmetric double quantum waveguide. The waveguide system is weakly connected to two electron reservoirs, but strongly coupled to a single quantized photon cavity mode. A coupling window is placed between the waveguides to allow electron interference or inter-waveguide transport. The transient electron transport in the system is investigated using a quantum master equation. We present a cavity-photon tunable semiconductor quantum waveguide implementation of an inverter quantum gate, in which the output of the waveguide system may be selected via the selection of an appropriate photon number or “photon frequency” of the cavity. In addition, the importance of the photon polarization in the cavity, that is, either parallel or perpendicular to the direction of electron propagation in the waveguide system is demonstrated.

URL arXiv, DOI BibTeX@article{abdullah2014cavity, author = "Abdullah, Nzar Rauf and Tang, Chi-Shung and Manolescu, Andrei and Gudmundsson, Vidar", title = "Cavity-photon-switched coherent transient transport in a double quantum waveguide", journal = "Journal of Applied Physics", year = 2014, volume = 116, number = 23, eid = 233104, pages = "-", url = "http://scitation.aip.org/content/aip/journal/jap/116/23/10.1063/1.4904907", doi = "http://dx.doi.org/10.1063/1.4904907", arxiv = "http://arxiv.org/abs/1410.4890", abstract = "We study a cavity-photon-switched coherent electron transport in a symmetric double quantum waveguide. The waveguide system is weakly connected to two electron reservoirs, but strongly coupled to a single quantized photon cavity mode. A coupling window is placed between the waveguides to allow electron interference or inter-waveguide transport. The transient electron transport in the system is investigated using a quantum master equation. We present a cavity-photon tunable semiconductor quantum waveguide implementation of an inverter quantum gate, in which the output of the waveguide system may be selected via the selection of an appropriate photon number or “photon frequency” of the cavity. In addition, the importance of the photon polarization in the cavity, that is, either parallel or perpendicular to the direction of electron propagation in the waveguide system is demonstrated." }

G Thorgilsson, G Viktorsson and S I Erlingsson.

**Recursive Greenʼs function method for multi-terminal nanostructures**.*Journal of Computational Physics*261, 256 - 266 (2014).

Abstract Abstract We present and review an efficient method to calculate the retarded Greenʼs function in multi-terminal nanostructures; which is needed in order to calculate the conductance through the system and the local particle densities within it. The method uses the recursive Greenʼs function method after the discretized Hamilton matrix has been properly partitioned. We show that this method, the circular slicing scheme, can be modified to accommodate multi-terminal systems as well as the traditional two-terminal systems. Furthermore, we show that the performance and robustness of the circular slicing scheme is on par with other advanced methods and is well suited for large variety of multi-terminal geometries. We end by giving an example of how the method can be used to calculate transport in a non-trivial multi-terminal geometry.

URL arXiv, DOI BibTeX@article{Thorgilsson2014256, title = "Recursive Greenʼs function method for multi-terminal nanostructures", journal = "Journal of Computational Physics", volume = 261, number = 0, pages = "256 - 266", year = 2014, note = "", issn = "0021-9991", doi = "10.1016/j.jcp.2013.12.054", url = "http://www.sciencedirect.com/science/article/pii/S0021999114000096", author = "G. Thorgilsson and G. Viktorsson and S.I. Erlingsson", keywords = "Multi-terminal nanostructures", abstract = "Abstract We present and review an efficient method to calculate the retarded Greenʼs function in multi-terminal nanostructures; which is needed in order to calculate the conductance through the system and the local particle densities within it. The method uses the recursive Greenʼs function method after the discretized Hamilton matrix has been properly partitioned. We show that this method, the circular slicing scheme, can be modified to accommodate multi-terminal systems as well as the traditional two-terminal systems. Furthermore, we show that the performance and robustness of the circular slicing scheme is on par with other advanced methods and is well suited for large variety of multi-terminal geometries. We end by giving an example of how the method can be used to calculate transport in a non-trivial multi-terminal geometry.", arxiv = "http://arxiv.org/abs/1305.7363" }

Nzar Rauf Abdullah, Chi-Shung Tang, Andrei Manolescu and Vidar Gudmundsson.

**Delocalization of electrons by cavity photons in transport through a quantum dot molecule**.*Physica E: Low-dimensional Systems and Nanostructures*, - (2014).

Abstract Abstract We present results on cavity-photon-assisted electron transport through two lateral quantum dots embedded in a finite quantum wire. The double quantum dot system is weakly connected to two leads and strongly coupled to a single quantized photon cavity mode with initially two linearly polarized photons in the cavity. Including the full electron-photon interaction, the transient current controlled by a plunger-gate in the central system is studied by using quantum master equation. Without a photon cavity, two resonant current peaks are observed in the range selected for the plunger gate voltage: The ground state peak, and the peak corresponding to the first-excited state. The current in the ground state is higher than in the first-excited state due to their different symmetry. In a photon cavity with the photon field polarized along or perpendicular to the transport direction, two extra side peaks are found, namely, photon-replica of the ground state and photon-replica of the first-excited state. The side-peaks are caused by photon-assisted electron transport, with multiphoton absorption processes for up to three photons during an electron tunneling process. The inter-dot tunneling in the ground state can be controlled by the photon cavity in the case of the photon field polarized along the transport direction. The electron charge is delocalized from the dots by the photon cavity. Furthermore, the current in the photon-induced side-peaks can be strongly enhanced by increasing the electron-photon coupling strength for the case of photons polarized along the transport direction.

URL arXiv, DOI BibTeX@article{RaufAbdullah2014, title = "Delocalization of electrons by cavity photons in transport through a quantum dot molecule", journal = "Physica E: Low-dimensional Systems and Nanostructures", volume = "", number = 0, pages = "-", year = 2014, note = "", issn = "1386-9477", doi = "10.1016/j.physe.2014.07.030", url = "http://www.sciencedirect.com/science/article/pii/S1386947714002938", author = "Nzar Rauf Abdullah and Chi-Shung Tang and Andrei Manolescu and Vidar Gudmundsson", keywords = "Electro-optical effects", abstract = "Abstract We present results on cavity-photon-assisted electron transport through two lateral quantum dots embedded in a finite quantum wire. The double quantum dot system is weakly connected to two leads and strongly coupled to a single quantized photon cavity mode with initially two linearly polarized photons in the cavity. Including the full electron-photon interaction, the transient current controlled by a plunger-gate in the central system is studied by using quantum master equation. Without a photon cavity, two resonant current peaks are observed in the range selected for the plunger gate voltage: The ground state peak, and the peak corresponding to the first-excited state. The current in the ground state is higher than in the first-excited state due to their different symmetry. In a photon cavity with the photon field polarized along or perpendicular to the transport direction, two extra side peaks are found, namely, photon-replica of the ground state and photon-replica of the first-excited state. The side-peaks are caused by photon-assisted electron transport, with multiphoton absorption processes for up to three photons during an electron tunneling process. The inter-dot tunneling in the ground state can be controlled by the photon cavity in the case of the photon field polarized along the transport direction. The electron charge is delocalized from the dots by the photon cavity. Furthermore, the current in the photon-induced side-peaks can be strongly enhanced by increasing the electron-photon coupling strength for the case of photons polarized along the transport direction.", arxiv = "http://arxiv.org/abs/1403.0382" }

Vidar Gudmundsson, Sigtryggur Hauksson, Arni Johnsen, Gilbert Reinisch, Andrei Manolescu, Christophe Besse and Guillaume Dujardin.

**Excitation of radial collective modes in a quantum dot: Beyond linear response**.*Annalen der Physik*526, 235–248 (2014).

Abstract The recent results on the linear breathing mode of the excitation spectrum of a quantum dot obtained by McDonald et. al [Phys. Rev. Lett. 111, 256801 (2013)] are extended to the nonlinear regime. To accomplish this and analyze the results the response of five different models of two interacting electrons in a quantum dot to an external short lived radial excitation that is strong enough to excite the system well beyond the linear response regime is compared. The models considered describe the Coulomb interaction between the electrons in different ways ranging from mean-field approaches to configuration interaction (CI) models, where the two-electron Hamiltonian is diagonalized in a large truncated Fock space. The radially symmetric excitation is selected in order to severely put to test the different approaches to describe the interaction and correlations of an electron system in a nonequilibrium state. As can be expected for the case of only two electrons none of the mean-field models can in full details reproduce the results obtained by the CI model. Nonetheless, some linear and nonlinear characteristics are reproduced reasonably well. All the models show activation of an increasing number of collective modes as the strength of the excitation is increased. By varying slightly the confinement potential of the dot it was observed how sensitive the properties of the excitation spectrum are to the Coulomb interaction and its correlation effects. In order to approach closer the question of nonlinearity one of the mean-field models has been solved directly in a nonlinear fashion without resorting to iterations.

URL arXiv, DOI BibTeX@article{ANDP:ANDP201400048, author = "Gudmundsson, Vidar and Hauksson, Sigtryggur and Johnsen, Arni and Reinisch, Gilbert and Manolescu, Andrei and Besse, Christophe and Dujardin, Guillaume", title = "Excitation of radial collective modes in a quantum dot: Beyond linear response", journal = "Annalen der Physik", volume = 526, number = "5-6", issn = "1521-3889", url = "http://dx.doi.org/10.1002/andp.201400048", doi = "10.1002/andp.201400048", pages = "235--248", year = 2014, abstract = "The recent results on the linear breathing mode of the excitation spectrum of a quantum dot obtained by McDonald et. al [Phys. Rev. Lett. 111, 256801 (2013)] are extended to the nonlinear regime. To accomplish this and analyze the results the response of five different models of two interacting electrons in a quantum dot to an external short lived radial excitation that is strong enough to excite the system well beyond the linear response regime is compared. The models considered describe the Coulomb interaction between the electrons in different ways ranging from mean-field approaches to configuration interaction (CI) models, where the two-electron Hamiltonian is diagonalized in a large truncated Fock space. The radially symmetric excitation is selected in order to severely put to test the different approaches to describe the interaction and correlations of an electron system in a nonequilibrium state. As can be expected for the case of only two electrons none of the mean-field models can in full details reproduce the results obtained by the CI model. Nonetheless, some linear and nonlinear characteristics are reproduced reasonably well. All the models show activation of an increasing number of collective modes as the strength of the excitation is increased. By varying slightly the confinement potential of the dot it was observed how sensitive the properties of the excitation spectrum are to the Coulomb interaction and its correlation effects. In order to approach closer the question of nonlinearity one of the mean-field models has been solved directly in a nonlinear fashion without resorting to iterations.", arxiv = "http://arxiv.org/abs/1311.3252" }

A Manolescu, D C Marinescu and T D Stanescu.

**Coulomb interaction effects on the Majorana states in quantum wires**.*Journal of Physics: Condensed Matter*26, 172203 (2014).

Abstract The stability of the Majorana modes in the presence of a repulsive interaction is studied in the standard semiconductor wire–metallic superconductor configuration. The effects of short-range Coulomb interaction, which is incorporated using a purely repulsive δ -function to model the strong screening effect due to the presence of the superconductor, are determined within a Hartree–Fock approximation of the effective Bogoliubov–De Gennes Hamiltonian that describes the low-energy physics of the wire. Through a numerical diagonalization procedure we obtain interaction corrections to the single particle eigenstates and calculate the extended topological phase diagram in terms of the chemical potential and the Zeeman energy. We find that, for a fixed Zeeman energy, the interaction shifts the phase boundaries to a higher chemical potential, whereas for a fixed chemical potential this shift can occur either at lower or higher Zeeman energies. These effects can be interpreted as a renormalization of the g-factor due to the interaction. The minimum Zeeman energy needed to realize Majorana fermions decreases with the increasing strength of the Coulomb repulsion. Furthermore, we find that in wires with multi-band occupancy this effect can be enhanced by increasing the chemical potential, i.e. by occupying higher energy bands.

URL arXiv, DOI BibTeX@article{0953-8984-26-17-172203, author = "A Manolescu and D C Marinescu and T D Stanescu", title = "Coulomb interaction effects on the Majorana states in quantum wires", journal = "Journal of Physics: Condensed Matter", volume = 26, number = 17, pages = 172203, url = "http://stacks.iop.org/0953-8984/26/i=17/a=172203", year = 2014, doi = "10.1088/0953-8984/26/17/172203", abstract = "The stability of the Majorana modes in the presence of a repulsive interaction is studied in the standard semiconductor wire–metallic superconductor configuration. The effects of short-range Coulomb interaction, which is incorporated using a purely repulsive δ -function to model the strong screening effect due to the presence of the superconductor, are determined within a Hartree–Fock approximation of the effective Bogoliubov–De Gennes Hamiltonian that describes the low-energy physics of the wire. Through a numerical diagonalization procedure we obtain interaction corrections to the single particle eigenstates and calculate the extended topological phase diagram in terms of the chemical potential and the Zeeman energy. We find that, for a fixed Zeeman energy, the interaction shifts the phase boundaries to a higher chemical potential, whereas for a fixed chemical potential this shift can occur either at lower or higher Zeeman energies. These effects can be interpreted as a renormalization of the g-factor due to the interaction. The minimum Zeeman energy needed to realize Majorana fermions decreases with the increasing strength of the Coulomb repulsion. Furthermore, we find that in wires with multi-band occupancy this effect can be enhanced by increasing the chemical potential, i.e. by occupying higher energy bands.", arxiv = "http://arxiv.org/abs/1312.3888" }

Thorsten Arnold, Chi-Shung Tang, Andrei Manolescu and Vidar Gudmundsson.

**Effects of geometry and linearly polarized cavity photons on charge and spin currents in a quantum ring with spin-orbit interactions**.*The European Physical Journal B*87 (2014).

Abstract We calculate the persistent charge and spin polarization current inside a finite-width quantum ring of realistic geometry as a function of the strength of the Rashba or Dresselhaus spin-orbit interaction. The time evolution in the transient regime of the two-dimensional (2D) quantum ring connected to electrically biased semi-infinite leads is governed by a time-convolutionless non-Markovian generalized master equation. The electrons are correlated via Coulomb interaction. In addition, the ring is embedded in a photon cavity with a single mode of linearly polarized photon field, which is polarized either perpendicular or parallel to the charge transport direction. To analyze carefully the physical effects, we compare to the analytical results of the toy model of a one-dimensional (1D) ring of non-interacting electrons with spin-orbit coupling. We find a pronounced charge current dip associated with many-electron level crossings at the Aharonov-Casher phase ΔΦ = π, which can be disguised by linearly polarized light. Qualitative agreement is found for the spin polarization currents of the 1D and 2D ring. Quantitatively, however, the spin polarization currents are weaker in the more realistic 2D ring, especially for weak spin-orbit interaction, but can be considerably enhanced with the aid of a linearly polarized electromagnetic field. Specific spin polarization current symmetries relating the Dresselhaus spin-orbit interaction case to the Rashba one are found to hold for the 2D ring, which is embedded in the photon cavity.

URL arXiv, DOI BibTeX@article{Arnold50144, year = 2014, issn = "1434-6028", journal = "The European Physical Journal B", eid = 113, volume = 87, number = 5, doi = "10.1140/epjb/e2014-50144-y", title = "Effects of geometry and linearly polarized cavity photons on charge and spin currents in a quantum ring with spin-orbit interactions", url = "http://dx.doi.org/10.1140/epjb/e2014-50144-y", publisher = "Springer Berlin Heidelberg", keywords = "Mesoscopic and Nanoscale Systems", author = "Arnold, Thorsten and Tang, Chi-Shung and Manolescu, Andrei and Gudmundsson, Vidar", language = "English", abstract = "We calculate the persistent charge and spin polarization current inside a finite-width quantum ring of realistic geometry as a function of the strength of the Rashba or Dresselhaus spin-orbit interaction. The time evolution in the transient regime of the two-dimensional (2D) quantum ring connected to electrically biased semi-infinite leads is governed by a time-convolutionless non-Markovian generalized master equation. The electrons are correlated via Coulomb interaction. In addition, the ring is embedded in a photon cavity with a single mode of linearly polarized photon field, which is polarized either perpendicular or parallel to the charge transport direction. To analyze carefully the physical effects, we compare to the analytical results of the toy model of a one-dimensional (1D) ring of non-interacting electrons with spin-orbit coupling. We find a pronounced charge current dip associated with many-electron level crossings at the Aharonov-Casher phase ΔΦ = π, which can be disguised by linearly polarized light. Qualitative agreement is found for the spin polarization currents of the 1D and 2D ring. Quantitatively, however, the spin polarization currents are weaker in the more realistic 2D ring, especially for weak spin-orbit interaction, but can be considerably enhanced with the aid of a linearly polarized electromagnetic field. Specific spin polarization current symmetries relating the Dresselhaus spin-orbit interaction case to the Rashba one are found to hold for the 2D ring, which is embedded in the photon cavity.", arxiv = "http://arxiv.org/abs/1310.5870" }

Thorsten Arnold, Chi-Shung Tang, Andrei Manolescu and Vidar Gudmundsson.

**Impact of a circularly polarized cavity photon field on the charge and spin flow through an Aharonov–Casher ring**.*Physica E: Low-dimensional Systems and Nanostructures*60, 170 - 182 (2014).

Abstract Abstract We explore the influence of a circularly polarized cavity photon field on the transport properties of a finite-width ring, in which the electrons are subject to spin–orbit and Coulomb interaction. The quantum ring is embedded in an electromagnetic cavity and described by “exact” numerical diagonalization. We study the case that the cavity photon field is circularly polarized and compare it to the linearly polarized case. The quantum device is moreover coupled to external, electrically biased leads. The time propagation in the transient regime is described by a non-Markovian generalized master equation. We find that the spin polarization and the spin photocurrents of the quantum ring are largest for circularly polarized photon field and destructive Aharonov–Casher (AC) phase interference. The charge current suppression dip due to the destructive AC phase becomes threefold under the circularly polarized photon field as the interaction of the electrons׳ angular momentum and spin angular momentum of light causes many-body level splitting leading to three many-body level crossing locations instead of one. The circular charge current inside the ring, which is induced by the circularly polarized photon field, is found to be suppressed in a much wider range around the destructive AC phase than the lead-device-lead charge current. The charge current can be directed through one of the two ring arms with the help of the circularly polarized photon field, but is superimposed by vortices of smaller scale. Unlike the charge photocurrent, the flow direction of the spin photocurrent is found to be independent of the handedness of the circularly polarized photon field.

URL arXiv, DOI BibTeX@article{Arnold2014170, title = "Impact of a circularly polarized cavity photon field on the charge and spin flow through an Aharonov–Casher ring", journal = "Physica E: Low-dimensional Systems and Nanostructures", volume = 60, number = 0, pages = "170 - 182", year = 2014, note = "", issn = "1386-9477", doi = "10.1016/j.physe.2014.02.024", url = "http://www.sciencedirect.com/science/article/pii/S138694771400085X", author = "Thorsten Arnold and Chi-Shung Tang and Andrei Manolescu and Vidar Gudmundsson", keywords = "Circularly polarized photon field", abstract = "Abstract We explore the influence of a circularly polarized cavity photon field on the transport properties of a finite-width ring, in which the electrons are subject to spin–orbit and Coulomb interaction. The quantum ring is embedded in an electromagnetic cavity and described by “exact” numerical diagonalization. We study the case that the cavity photon field is circularly polarized and compare it to the linearly polarized case. The quantum device is moreover coupled to external, electrically biased leads. The time propagation in the transient regime is described by a non-Markovian generalized master equation. We find that the spin polarization and the spin photocurrents of the quantum ring are largest for circularly polarized photon field and destructive Aharonov–Casher (AC) phase interference. The charge current suppression dip due to the destructive \{AC\} phase becomes threefold under the circularly polarized photon field as the interaction of the electrons׳ angular momentum and spin angular momentum of light causes many-body level splitting leading to three many-body level crossing locations instead of one. The circular charge current inside the ring, which is induced by the circularly polarized photon field, is found to be suppressed in a much wider range around the destructive \{AC\} phase than the lead-device-lead charge current. The charge current can be directed through one of the two ring arms with the help of the circularly polarized photon field, but is superimposed by vortices of smaller scale. Unlike the charge photocurrent, the flow direction of the spin photocurrent is found to be independent of the handedness of the circularly polarized photon field.", arxiv = "http://arxiv.org/abs/1311.3235" }

Gilbert Reinisch, Vidar Gudmundsson and Andrei Manolescu.

**Coherent nonlinear quantum model for composite fermions**.*Physics Letters A*378, 1566 - 1570 (2014).

Abstract Abstract Originally proposed by Read [1] and Jain [2], the so-called “composite-fermion” is a phenomenological quasi-particle resulting from the attachment of two local flux quanta, seen as nonlocal vortices, to electrons situated on a two-dimensional (2D) surface embedded in a strong orthogonal magnetic field. In this Letter this phenomenon is described as a highly-nonlinear and coherent mean-field quantum process of the soliton type by use of a 2D stationary Schrödinger–Poisson differential model with only two Coulomb-interacting electrons. At filling factor ν = 1 3 of the lowest Landau level the solution agrees with both the exact two-electron antisymmetric Schrödinger wavefunction and with Laughlin's Jastrow-type guess for the fractional quantum Hall effect, hence providing this latter with a tentative physical justification deduced from the experimental results and based on first principles.

URL arXiv, DOI BibTeX@article{Reinisch20141566, title = "Coherent nonlinear quantum model for composite fermions", journal = "Physics Letters A", volume = 378, number = 21, pages = "1566 - 1570", year = 2014, note = "", issn = "0375-9601", doi = "10.1016/j.physleta.2014.03.050", url = "http://www.sciencedirect.com/science/article/pii/S0375960114003272", author = "Gilbert Reinisch and Vidar Gudmundsson and Andrei Manolescu", keywords = "Quasi-particles", abstract = "Abstract Originally proposed by Read [1] and Jain [2], the so-called “composite-fermion” is a phenomenological quasi-particle resulting from the attachment of two local flux quanta, seen as nonlocal vortices, to electrons situated on a two-dimensional (2D) surface embedded in a strong orthogonal magnetic field. In this Letter this phenomenon is described as a highly-nonlinear and coherent mean-field quantum process of the soliton type by use of a 2D stationary Schrödinger–Poisson differential model with only two Coulomb-interacting electrons. At filling factor ν = 1 3 of the lowest Landau level the solution agrees with both the exact two-electron antisymmetric Schrödinger wavefunction and with Laughlin's Jastrow-type guess for the fractional quantum Hall effect, hence providing this latter with a tentative physical justification deduced from the experimental results and based on first principles.", arxiv = "http://arxiv.org/abs/1306.6869" }

Halldor G Svavarsson, Sigurbjorn Einarsson and Asa Brynjolfsdottir.

**Adsorption applications of unmodified geothermal silica**.*Geothermics*50, 30 - 34 (2014).

Abstract Abstract Silica, precipitated out of geothermal fluid discharged from a geothermal powerplant in Svartsengi on the Reykjanes peninsula in Iceland, was used as a chromatographic adsorbent to extract blue colored protein, C-phycocyanin, from coccoid blue-green algae. The only supplement used was salt obtained by evaporating the geothermal fluid. Analysis of the silica, using scanning electron microscopy, X-ray diffractometry and Brunauer–Emmett–Teller (BET) adsorption confirmed it has a high specific surface area and is amorphous. Upon adsorption and subsequent elution the purity of the extracted protein, measured as the ratio of the light absorbance of 620 and 280 nm, increased from 0.5 to above 2.0. Our results could facilitate utilization of a mostly unused byproduct of geothermal powerplants as chromatographic material.

URL, DOI BibTeX@article{Svavarsson201430, title = "Adsorption applications of unmodified geothermal silica", journal = "Geothermics", volume = 50, number = 0, pages = "30 - 34", year = 2014, note = "", issn = "0375-6505", doi = "10.1016/j.geothermics.2013.08.001", url = "http://www.sciencedirect.com/science/article/pii/S0375650513000576", author = "Halldor G. Svavarsson and Sigurbjorn Einarsson and Asa Brynjolfsdottir", keywords = "Phycocyanin", abstract = "Abstract Silica, precipitated out of geothermal fluid discharged from a geothermal powerplant in Svartsengi on the Reykjanes peninsula in Iceland, was used as a chromatographic adsorbent to extract blue colored protein, C-phycocyanin, from coccoid blue-green algae. The only supplement used was salt obtained by evaporating the geothermal fluid. Analysis of the silica, using scanning electron microscopy, X-ray diffractometry and Brunauer–Emmett–Teller (BET) adsorption confirmed it has a high specific surface area and is amorphous. Upon adsorption and subsequent elution the purity of the extracted protein, measured as the ratio of the light absorbance of 620 and 280 nm, increased from 0.5 to above 2.0. Our results could facilitate utilization of a mostly unused byproduct of geothermal powerplants as chromatographic material." }

Tomas Orn Rosdahl, Andrei Manolescu and Vidar Gudmundsson.

**Spin and impurity effects on flux-periodic oscillations in core-shell nanowires**.*Phys. Rev. B*90, 035421 (July 2014).

Abstract We study the quantum mechanical states of electrons situated on a cylindrical surface of finite axial length to model a semiconductor core-shell nanowire. We calculate the conductance in the presence of a longitudinal magnetic field by weakly coupling the cylinder to semi-infinite leads. Spin effects are accounted for through Zeeman coupling and Rashba spin-orbit interaction (SOI). Emphasis is on manifestations of flux-periodic oscillations and we show how factors such as impurities, contact geometry, and spin affect them. Oscillations survive and remain periodic in the presence of impurities, noncircular contacts, and SOI, while Zeeman splitting results in aperiodicity, beating patterns, and additional background fluctuations. Our results are in qualitative agreement with recent magnetotransport experiments performed on GaAs/InAs core-shell nanowires. Lastly, we propose methods of data analysis for detecting the presence of Rashba SOI in core-shell systems and for estimating the electron g factor in the shell.

URL arXiv, DOI BibTeX@article{PhysRevB.90.035421, title = "Spin and impurity effects on flux-periodic oscillations in core-shell nanowires", author = "Rosdahl, Tomas Orn and Manolescu, Andrei and Gudmundsson, Vidar", journal = "Phys. Rev. B", volume = 90, issue = 3, pages = 035421, numpages = 11, year = 2014, month = "Jul", publisher = "American Physical Society", doi = "10.1103/PhysRevB.90.035421", url = "http://link.aps.org/doi/10.1103/PhysRevB.90.035421", abstract = "We study the quantum mechanical states of electrons situated on a cylindrical surface of finite axial length to model a semiconductor core-shell nanowire. We calculate the conductance in the presence of a longitudinal magnetic field by weakly coupling the cylinder to semi-infinite leads. Spin effects are accounted for through Zeeman coupling and Rashba spin-orbit interaction (SOI). Emphasis is on manifestations of flux-periodic oscillations and we show how factors such as impurities, contact geometry, and spin affect them. Oscillations survive and remain periodic in the presence of impurities, noncircular contacts, and SOI, while Zeeman splitting results in aperiodicity, beating patterns, and additional background fluctuations. Our results are in qualitative agreement with recent magnetotransport experiments performed on GaAs/InAs core-shell nanowires. Lastly, we propose methods of data analysis for detecting the presence of Rashba SOI in core-shell systems and for estimating the electron g factor in the shell.", arxiv = "http://arxiv.org/abs/1404.1798" }