G A Nemnes, C Goehry, T L Mitran, Adela Nicolaev, L Ion, S Antohe, N Plugaru and A Manolescu.

**Band alignment and charge transfer in rutile-TiO\(_2\)/CH\(_3\)NH\(_3\)PbI\(_3\)\(_-\)\(_x\)Cl\(_x\) interfaces**.*Phys. Chem. Chem. Phys.*17, 30417-30423 (2015).

Abstract Rutile-TiO\(_2\)/hybrid halide perovskite CH\(_3\)NH\(_3\)PbI\(_3\)\(_-\)\(_x\)Cl\(_x\) interfaces are investigated by ab initio density functional theory calculations. The role of chlorine in achieving enhanced solar cell power conversion efficiencies is in the focus of recent studies, which point to increased carrier mobilities, reduced recombination rates, a driven morphology evolution of the perovskite layer and improved carrier transport across the interface. As it was recently established that chlorine is preferentially localized in the vicinity of the interface and not in the bulk of the perovskite layer, we analyze the changes introduced in the electronic properties by varying the chlorine concentration near the interface. In particular, we discuss the effects introduced in the electronic band structure and show the role of chlorine in the enhanced electron injection into the rutile-TiO\(_2\) layer. Taking into account these implications, we discuss the conditions for optimizing the solar cell efficiency in terms of interfacial chlorine concentration.

URL, DOI BibTeX@article{C5CP05466D, author = "Nemnes, G. A. and Goehry, C. and Mitran, T. L. and Nicolaev, Adela and Ion, L. and Antohe, S. and Plugaru, N. and Manolescu, A.", title = "Band alignment and charge transfer in rutile-TiO\(_2\)/CH\(_3\)NH\(_3\)PbI\(_3\)\(_-\)\(_x\)Cl\(_x\) interfaces", journal = "Phys. Chem. Chem. Phys.", year = 2015, volume = 17, issue = 45, pages = "30417-30423", publisher = "The Royal Society of Chemistry", doi = "10.1039/C5CP05466D", url = "http://dx.doi.org/10.1039/C5CP05466D", abstract = "Rutile-TiO\(_2\)/hybrid halide perovskite CH\(_3\)NH\(_3\)PbI\(_3\)\(_-\)\(_x\)Cl\(_x\) interfaces are investigated by ab initio density functional theory calculations. The role of chlorine in achieving enhanced solar cell power conversion efficiencies is in the focus of recent studies{,} which point to increased carrier mobilities{,} reduced recombination rates{,} a driven morphology evolution of the perovskite layer and improved carrier transport across the interface. As it was recently established that chlorine is preferentially localized in the vicinity of the interface and not in the bulk of the perovskite layer{,} we analyze the changes introduced in the electronic properties by varying the chlorine concentration near the interface. In particular{,} we discuss the effects introduced in the electronic band structure and show the role of chlorine in the enhanced electron injection into the rutile-TiO\(_2\) layer. Taking into account these implications{,} we discuss the conditions for optimizing the solar cell efficiency in terms of interfacial chlorine concentration." }

Marjan Ilkov, Kristinn Torfason, Andrei Manolescu and Ágúst Valfells.

**Terahertz pulsed photogenerated current in microdiodes at room temperature**.*Applied Physics Letters*107, (2015).

Abstract Space-charge modulation of the current in a vacuum diode under photoemission leads to the formation of beamlets with time periodicity corresponding to THz frequencies. We investigate the effect of the emitter temperature and internal space-charge forces on the formation and persistence of the beamlets. We find that temperature effects are most important for beam degradation at low values of the applied electric field, whereas at higher fields, intra-beamlet space-charge forces are dominant. The current modulation is most robust when there is only one beamlet present in the diode gap at a time, corresponding to a macroscopic version of the Coulomb blockade. It is shown that a vacuum microdiode can operate quite well as a tunable THz oscillator at room temperature with an applied electric field above 10 MV/m and a diode gap of the order of 100 nm.

URL arXiv, DOI BibTeX@article{ilkov2015terahertz, author = "Ilkov, Marjan and Torfason, Kristinn and Manolescu, Andrei and Valfells, Ágúst", title = "Terahertz pulsed photogenerated current in microdiodes at room temperature", journal = "Applied Physics Letters", year = 2015, volume = 107, number = 20, eid = 203508, pages = "", url = "http://scitation.aip.org/content/aip/journal/apl/107/20/10.1063/1.4936176", doi = "10.1063/1.4936176", abstract = "Space-charge modulation of the current in a vacuum diode under photoemission leads to the formation of beamlets with time periodicity corresponding to THz frequencies. We investigate the effect of the emitter temperature and internal space-charge forces on the formation and persistence of the beamlets. We find that temperature effects are most important for beam degradation at low values of the applied electric field, whereas at higher fields, intra-beamlet space-charge forces are dominant. The current modulation is most robust when there is only one beamlet present in the diode gap at a time, corresponding to a macroscopic version of the Coulomb blockade. It is shown that a vacuum microdiode can operate quite well as a tunable THz oscillator at room temperature with an applied electric field above 10 MV/m and a diode gap of the order of 100 nm.", arxiv = "http://arxiv.org/abs/1508.06308" }

Błażej Jaworowski, Andrei Manolescu and Paweł Potasz.

**Fractional Chern insulator phase at the transition between checkerboard and Lieb lattices**.*Phys. Rev. B*92, 245119 (December 2015).

Abstract The stability of the ν=1/3 fractional Chern insulator (FCI) phase is analyzed on the example of a checkerboard lattice undergoing a transition into a Lieb lattice. The transition is performed by the addition of a second sublattice, whose coupling to the checkerboard sites is controlled by sublattice staggered potential. We investigate the influence of these sites on the many-body energy gap between three lowest energy states and the fourth state. We consider cases with different complex phases acquired in hopping and a model with a flattened topologically nontrivial band. We find that an interaction with the additional sites either open the single-particle gap or enlarge the existing one, which translates into similar effect on the many-particle gap. By looking at Berry curvature flatness we notice its strong correlation with the magnitude of the many-body energy gap, suggesting that the main mechanism of the FCI stabilization by additional atoms is via their influence on the Berry curvature. Evidence of the FCI phase for a region in a parameter space with larger energy gap is shown by looking at momenta of the threefold degenerate ground state, spectral flow, and quasihole excitation spectrum.

URL arXiv, DOI BibTeX@article{PhysRevB.92.245119, title = "Fractional Chern insulator phase at the transition between checkerboard and Lieb lattices", author = "Błażej Jaworowski and Manolescu, Andrei and Potasz, Paweł", journal = "Phys. Rev. B", volume = 92, issue = 24, pages = 245119, numpages = 7, year = 2015, month = "Dec", publisher = "American Physical Society", arxiv = "http://arxiv.org/abs/1508.04399", doi = "10.1103/PhysRevB.92.245119", url = "http://link.aps.org/doi/10.1103/PhysRevB.92.245119", abstract = "The stability of the ν=1/3 fractional Chern insulator (FCI) phase is analyzed on the example of a checkerboard lattice undergoing a transition into a Lieb lattice. The transition is performed by the addition of a second sublattice, whose coupling to the checkerboard sites is controlled by sublattice staggered potential. We investigate the influence of these sites on the many-body energy gap between three lowest energy states and the fourth state. We consider cases with different complex phases acquired in hopping and a model with a flattened topologically nontrivial band. We find that an interaction with the additional sites either open the single-particle gap or enlarge the existing one, which translates into similar effect on the many-particle gap. By looking at Berry curvature flatness we notice its strong correlation with the magnitude of the many-body energy gap, suggesting that the main mechanism of the FCI stabilization by additional atoms is via their influence on the Berry curvature. Evidence of the FCI phase for a region in a parameter space with larger energy gap is shown by looking at momenta of the threefold degenerate ground state, spectral flow, and quasihole excitation spectrum." }

Charles Goehry, George Alexandru Nemnes and Andrei Manolescu.

**Collective Behavior of Molecular Dipoles in CH\(_3\)NH\(_3\)PbI\(_3\)**.*The Journal of Physical Chemistry C*119, 19674-19680 (2015).

Abstract Using ab-initio molecular dynamics, we report a detailed exploration of the thermal motion occurring in perovskite crystals of formula CH\(_3\)NH\(_3\)PbI\(_3\). We exploit the data generated to obtain estimates of the rotational relaxation time of the cation (CH\(_3\)NH\(_3\)+). We examine the tetragonal and cubic phase, as both may be present under operational conditions. Influenced by each other, and by the tilting of PBI\(_6\) octahedra, cations undergo collective motion as their contribution to polarization does not vanish. We thereby qualitatively describe the modus operandi of formation of microscopic ferroelectric domains.

URL, DOI BibTeX@article{jpcc-5b05823, author = "Goehry, Charles and Nemnes, George Alexandru and Manolescu, Andrei", title = "Collective Behavior of Molecular Dipoles in CH\(_3\)NH\(_3\)PbI\(_3\)", journal = "The Journal of Physical Chemistry C", volume = 119, number = 34, pages = "19674-19680", year = 2015, doi = "10.1021/acs.jpcc.5b05823", url = "http://dx.doi.org/10.1021/acs.jpcc.5b05823", eprint = "http://dx.doi.org/10.1021/acs.jpcc.5b05823", abstract = "Using ab-initio molecular dynamics, we report a detailed exploration of the thermal motion occurring in perovskite crystals of formula CH\(_3\)NH\(_3\)PbI\(_3\). We exploit the data generated to obtain estimates of the rotational relaxation time of the cation (CH\(_3\)NH\(_3\)+). We examine the tetragonal and cubic phase, as both may be present under operational conditions. Influenced by each other, and by the tilting of PBI\(_6\) octahedra, cations undergo collective motion as their contribution to polarization does not vanish. We thereby qualitatively describe the modus operandi of formation of microscopic ferroelectric domains." }

A Sitek, V Gudmundsson and A Manolescu.

**Symmetry dependent electron localization and optical absorption of polygonal quantum rings**.

In*Transparent Optical Networks (ICTON), 2015 17th International Conference on*. (July 2015), 1-4.

Abstract We compare energy spectra, electron localization and optical absorption of square and diamond quantum rings and analyze how sample geometry affects those features. We show that low energy levels of diamond rings form two groups delocalized between opposite corners which results in increased number of optical transitions. We also show that contacts applied to corner areas allow for continuous change between square- and diamond-like behavior of the same sample, irrespective of its shape.

arXiv, DOI BibTeX@inproceedings{7193541, author = "Sitek, A. and Gudmundsson, V. and Manolescu, A.", booktitle = "Transparent Optical Networks (ICTON), 2015 17th International Conference on", title = "Symmetry dependent electron localization and optical absorption of polygonal quantum rings", year = 2015, pages = "1-4", abstract = "We compare energy spectra, electron localization and optical absorption of square and diamond quantum rings and analyze how sample geometry affects those features. We show that low energy levels of diamond rings form two groups delocalized between opposite corners which results in increased number of optical transitions. We also show that contacts applied to corner areas allow for continuous change between square- and diamond-like behavior of the same sample, irrespective of its shape.", keywords = "light absorption;quantum wires;optical transition;polygonal quantum rings optical absorption;symmetry dependent electron localization;Absorption;Diamonds;Electron optics;Energy states;Integrated optics;Nanowires;Probability distribution;absorption;core-multi-shell structures;polygonal quantum rings", doi = "10.1109/ICTON.2015.7193541", arxiv = "http://arxiv.org/abs/1505.00207", month = "July" }

Sigurdur I Erlingsson, Andrei Manolescu and D C Marinescu.

**Asymmetric Landau bands due to spin–orbit coupling**.*Journal of Physics: Condensed Matter*27, 225303 (2015).

Abstract We show that the Landau bands obtained in a two-dimensional lateral semiconductor superlattice with spin–orbit coupling (SOC) of the Rashba/Dresselhaus type, linear in the electron momentum, placed in a tilted magnetic field, do not follow the symmetry of the spatial modulation. Moreover, this phenomenology is found to depend on the relative tilt of magnetic field and on the SOC type: (a) when only Rashba SOC exists and the magnetic field is tilted in the direction of the superlattice (b) Dresselhaus SOC exists and the magnetic field is tilted in the direction perpendicular to the superlattice. Consequently, measurable properties of the modulated system become anisotropic in a tilted magnetic field when the field is conically rotated around the z axis, at a fixed polar angle, as we demonstrate by calculating the resistivity and the magnetization.

URL arXiv, DOI BibTeX@article{0953-8984-27-22-225303, author = "Sigurdur I Erlingsson and Andrei Manolescu and D C Marinescu", title = "Asymmetric Landau bands due to spin–orbit coupling", journal = "Journal of Physics: Condensed Matter", volume = 27, number = 22, pages = 225303, url = "http://stacks.iop.org/0953-8984/27/i=22/a=225303", year = 2015, doi = "10.1088/0953-8984/27/22/225303", abstract = "We show that the Landau bands obtained in a two-dimensional lateral semiconductor superlattice with spin–orbit coupling (SOC) of the Rashba/Dresselhaus type, linear in the electron momentum, placed in a tilted magnetic field, do not follow the symmetry of the spatial modulation. Moreover, this phenomenology is found to depend on the relative tilt of magnetic field and on the SOC type: (a) when only Rashba SOC exists and the magnetic field is tilted in the direction of the superlattice (b) Dresselhaus SOC exists and the magnetic field is tilted in the direction perpendicular to the superlattice. Consequently, measurable properties of the modulated system become anisotropic in a tilted magnetic field when the field is conically rotated around the z axis, at a fixed polar angle, as we demonstrate by calculating the resistivity and the magnetization.", arxiv = "http://arxiv.org/abs/1504.04699" }

Jeremy Capps, D C Marinescu and Andrei Manolescu.

**Coulomb interaction effects in a two-dimensional quantum well with spin-orbit interaction**.*Phys. Rev. B*91, 165301 (April 2015).

Abstract Starting from general total-energy considerations, we demonstrate that the SU(2) spin-rotation symmetry and the resulting persistent helical state (PHS) predicted to occur in an electron system with equal Rashba-Dresselhaus coupling constants are not in fact realized. On account of the accidental degeneracy that appears in the single-particle spectrum, the Coulomb interaction favors the apparition of an itinerant antiferromagnetic (IAF) order characterized by a fractional polarization of fixed spatial orientation. Within the Hartree-Fock approximation, we obtain numerical results that describe the temperature evolution of the order parameter in the IAF state and determine the critical temperature of the transition to the paramagnetic state.

URL, DOI BibTeX@article{PhysRevB.91.165301, title = "Coulomb interaction effects in a two-dimensional quantum well with spin-orbit interaction", author = "Capps, Jeremy and Marinescu, D. C. and Manolescu, Andrei", journal = "Phys. Rev. B", volume = 91, issue = 16, pages = 165301, numpages = 8, year = 2015, month = "Apr", publisher = "American Physical Society", doi = "10.1103/PhysRevB.91.165301", url = "http://link.aps.org/doi/10.1103/PhysRevB.91.165301", abstract = "Starting from general total-energy considerations, we demonstrate that the SU(2) spin-rotation symmetry and the resulting persistent helical state (PHS) predicted to occur in an electron system with equal Rashba-Dresselhaus coupling constants are not in fact realized. On account of the accidental degeneracy that appears in the single-particle spectrum, the Coulomb interaction favors the apparition of an itinerant antiferromagnetic (IAF) order characterized by a fractional polarization of fixed spatial orientation. Within the Hartree-Fock approximation, we obtain numerical results that describe the temperature evolution of the order parameter in the IAF state and determine the critical temperature of the transition to the paramagnetic state." }

Anna Sitek, Llorenç Serra, Vidar Gudmundsson and Andrei Manolescu.

**Electron localization and optical absorption of polygonal quantum rings**.*Phys. Rev. B*91, 235429 (June 2015).

Abstract 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.

URL arXiv, DOI BibTeX@article{PhysRevB.91.235429, title = "Electron localization and optical absorption of polygonal quantum rings", author = "Sitek, Anna and Serra, Lloren\c{c} and Gudmundsson, Vidar and Manolescu, Andrei", journal = "Phys. Rev. B", volume = 91, issue = 23, pages = 235429, numpages = 10, year = 2015, month = "Jun", publisher = "American Physical Society", doi = "10.1103/PhysRevB.91.235429", arxiv = "http://arxiv.org/abs/1503.09186", url = "http://link.aps.org/doi/10.1103/PhysRevB.91.235429", abstract = "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." }

Vidar Gudmundsson, Anna Sitek, Pei-yi Lin, Nzar Rauf Abdullah, Chi-Shung Tang and Andrei Manolescu.

**Coupled Collective and Rabi Oscillations Triggered by Electron Transport through a Photon Cavity**.*ACS Photonics*2, 930-934 (2015).

Abstract We show how the switching on of electron transport through a system of two parallel quantum dots embedded in a short quantum wire in a photon cavity can trigger coupled Rabi and collective electron–photon oscillations. We select the initial state of the system to be an eigenstate of the closed system containing two Coulomb-interacting electrons with possibly few photons of a single cavity mode. The many-level quantum dots are described by a continuous potential. The Coulomb interaction and the para- and diamagnetic electron–photon interactions are treated by exact diagonalization in a truncated Fock space. To identify the collective modes, the results are compared for an open and a closed system with respect to the coupling to external electron reservoirs, or leads. We demonstrate that the vacuum Rabi oscillations can be seen in transport quantities as the current in and out of the system.

URL arXiv, DOI BibTeX@article{doi:10.1021/acsphotonics.5b00115, author = "Gudmundsson, Vidar and Sitek, Anna and Lin, Pei-yi and Abdullah, Nzar Rauf and Tang, Chi-Shung and Manolescu, Andrei", title = "Coupled Collective and Rabi Oscillations Triggered by Electron Transport through a Photon Cavity", journal = "ACS Photonics", volume = 2, number = 7, pages = "930-934", year = 2015, doi = "10.1021/acsphotonics.5b00115", arxiv = "http://arxiv.org/abs/1502.06242", url = "http://dx.doi.org/10.1021/acsphotonics.5b00115", eprint = "http://dx.doi.org/10.1021/acsphotonics.5b00115", abstract = "We show how the switching on of electron transport through a system of two parallel quantum dots embedded in a short quantum wire in a photon cavity can trigger coupled Rabi and collective electron–photon oscillations. We select the initial state of the system to be an eigenstate of the closed system containing two Coulomb-interacting electrons with possibly few photons of a single cavity mode. The many-level quantum dots are described by a continuous potential. The Coulomb interaction and the para- and diamagnetic electron–photon interactions are treated by exact diagonalization in a truncated Fock space. To identify the collective modes, the results are compared for an open and a closed system with respect to the coupling to external electron reservoirs, or leads. We demonstrate that the vacuum Rabi oscillations can be seen in transport quantities as the current in and out of the system." }

Kristinn Torfason, Agust Valfells and Andrei Manolescu.

**Molecular dynamics simulations of field emission from a planar nanodiode**.*Physics of Plasmas (1994-present)*22, - (2015).

Abstract High resolution molecular dynamics simulations with full Coulomb interactions of electrons are used to investigate field emission in planar nanodiodes. The effects of space-charge and emitter radius are examined and compared to previous results concerning transition from Fowler-Nordheim to Child-Langmuir current [Y. Y. Lau, Y. Liu, and R. K. Parker, Phys. Plasmas 1, 2082 (1994) and Y. Feng and J. P. Verboncoeur, Phys. Plasmas 13, 073105 (2006)]. The Fowler-Nordheim law is used to determine the current density injected into the system and the Metropolis-Hastings algorithm to find a favourable point of emission on the emitter surface. A simple fluid like model is also developed and its results are in qualitative agreement with the simulations.

URL arXiv, DOI BibTeX@article{4914855, author = "Torfason, Kristinn and Valfells, Agust and Manolescu, Andrei", title = "Molecular dynamics simulations of field emission from a planar nanodiode", journal = "Physics of Plasmas (1994-present)", year = 2015, volume = 22, number = 3, eid = 033109, pages = "-", url = "http://scitation.aip.org/content/aip/journal/pop/22/3/10.1063/1.4914855", doi = "http://dx.doi.org/10.1063/1.4914855", arxiv = "http://arxiv.org/abs/1412.4537", abstract = "High resolution molecular dynamics simulations with full Coulomb interactions of electrons are used to investigate field emission in planar nanodiodes. The effects of space-charge and emitter radius are examined and compared to previous results concerning transition from Fowler-Nordheim to Child-Langmuir current [Y. Y. Lau, Y. Liu, and R. K. Parker, Phys. Plasmas 1, 2082 (1994) and Y. Feng and J. P. Verboncoeur, Phys. Plasmas 13, 073105 (2006)]. The Fowler-Nordheim law is used to determine the current density injected into the system and the Metropolis-Hastings algorithm to find a favourable point of emission on the emitter surface. A simple fluid like model is also developed and its results are in qualitative agreement with the simulations." }

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

**Excitation spectra of a quantum ring embedded in a photon cavity**.*Journal of Optics*17, 015201 (2015).

Abstract We explore the response of a quantum ring system coupled to a photon cavity with a single mode when excited by a classical dipole field. We find that the energy oscillates between the electronic and photonic components of the system. The contribution of the linear and the quadratic terms in the vector potential to the electron–photon interaction energy are of similar magnitude, but opposite signs stressing the importance of retaining both in the model. Furthermore, we find different Fourier spectra for the oscillations of the center of charge and the oscillations of the mean photon number in time. The Fourier spectra are compared to the spectrum of the many-body (MB) states and selection rules discussed. In case of the center of charge oscillations, the dipole matrix elements preselect the allowed Bohr frequencies of the transitions, while for the oscillations of the mean photon number, the difference of the photon content of the MB states influences the selection rules.

URL arXiv, DOI BibTeX@article{2040-8986-17-1-015201, author = "Thorsten Arnold and Chi-Shung Tang and Andrei Manolescu and Vidar Gudmundsson", title = "Excitation spectra of a quantum ring embedded in a photon cavity", journal = "Journal of Optics", volume = 17, number = 1, pages = 015201, url = "http://stacks.iop.org/2040-8986/17/i=1/a=015201", year = 2015, arxiv = "http://arxiv.org/abs/1410.0174", doi = "10.1088/2040-8978/17/1/015201", abstract = "We explore the response of a quantum ring system coupled to a photon cavity with a single mode when excited by a classical dipole field. We find that the energy oscillates between the electronic and photonic components of the system. The contribution of the linear and the quadratic terms in the vector potential to the electron–photon interaction energy are of similar magnitude, but opposite signs stressing the importance of retaining both in the model. Furthermore, we find different Fourier spectra for the oscillations of the center of charge and the oscillations of the mean photon number in time. The Fourier spectra are compared to the spectrum of the many-body (MB) states and selection rules discussed. In case of the center of charge oscillations, the dipole matrix elements preselect the allowed Bohr frequencies of the transitions, while for the oscillations of the mean photon number, the difference of the photon content of the MB states influences the selection rules." }

Sigurdur I Erlingsson and Carlos J Egues.

**All-electron topological insulator in InAs double wells**.*Phys. Rev. B*91, 035312 (January 2015).

Abstract We show that electrons in ordinary III-V semiconductor double wells with an in-plane modulating periodic potential and interwell spin-orbit interaction are tunable topological insulators (TIs). Here the essential TI ingredients, namely, band inversion and the opening of an overall bulk gap in the spectrum arise, respectively, from (i) the combined effect of the double-well even-odd state splitting \(\Delta\)SAS together with the superlattice potential and (ii) the interband Rashba spin-orbit coupling \(\eta\). We corroborate our exact diagonalization results with an analytical nearly-free-electron description that allows us to derive an effective Bernevig-Hughes-Zhang model. Interestingly, the gate-tunable mass gap M drives a topological phase transition featuring a discontinuous Chern number at \(\Delta\)SAS\(\sim\)5.4meV. Finally, we explicitly verify the bulk-edge correspondence by considering a strip configuration and determining not only the bulk bands in the nontopological and topological phases but also the edge states and their Dirac-like spectrum in the topological phase. The edge electronic densities exhibit peculiar spatial oscillations as they decay away into the bulk. For concreteness, we present our results for InAs-based wells with realistic parameters

URL arXiv, DOI BibTeX@article{PhysRevB.91.035312, title = "All-electron topological insulator in InAs double wells", author = "Erlingsson, Sigurdur I. and Egues, J. Carlos", journal = "Phys. Rev. B", volume = 91, issue = 3, pages = 035312, numpages = 8, year = 2015, month = "Jan", publisher = "American Physical Society", doi = "10.1103/PhysRevB.91.035312", url = "http://link.aps.org/doi/10.1103/PhysRevB.91.035312", arxiv = "http://arxiv.org/abs/1312.2034", abstract = "We show that electrons in ordinary III-V semiconductor double wells with an in-plane modulating periodic potential and interwell spin-orbit interaction are tunable topological insulators (TIs). Here the essential TI ingredients, namely, band inversion and the opening of an overall bulk gap in the spectrum arise, respectively, from (i) the combined effect of the double-well even-odd state splitting \(\Delta\)SAS together with the superlattice potential and (ii) the interband Rashba spin-orbit coupling \(\eta\). We corroborate our exact diagonalization results with an analytical nearly-free-electron description that allows us to derive an effective Bernevig-Hughes-Zhang model. Interestingly, the gate-tunable mass gap M drives a topological phase transition featuring a discontinuous Chern number at \(\Delta\)SAS\(\sim\)5.4meV. Finally, we explicitly verify the bulk-edge correspondence by considering a strip configuration and determining not only the bulk bands in the nontopological and topological phases but also the edge states and their Dirac-like spectrum in the topological phase. The edge electronic densities exhibit peculiar spatial oscillations as they decay away into the bulk. For concreteness, we present our results for InAs-based wells with realistic parameters" }

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

**Coherent transient transport of interacting electrons through a quantum waveguide switch**.*Journal of Physics: Condensed Matter*27, 015301 (2015).

Abstract We investigate coherent electron-switching transport in a double quantum waveguide system in a perpendicular static or vanishing magnetic field. The finite symmetric double waveguide is connected to two semi-infinite leads from both ends. The double waveguide can be defined as two parallel finite quantum wires or waveguides coupled via a window to facilitate coherent electron inter-wire transport. By tuning the length of the coupling window, we observe oscillations in the net charge current and a maximum electron conductance for the energy levels of the two waveguides in resonance. The importance of the mutual Coulomb interaction between the electrons and the influence of two-electron states is clarified by comparing results with and without the interaction. Even though the Coulomb interaction can lift two-electron states out of the group of active transport states the length of the coupling window can be tuned to locate two very distinct transport modes in the system in the late transient regime before the onset of a steady state. A static external magnetic field and quantum-dots formed by side gates (side quantum dots) can be used to enhance the inter-waveguide transport which can serve to implement a quantum logic device. The fact that the device can be operated in the transient regime can be used to enhance its speed.

URL arXiv, DOI BibTeX@article{0953-8984-27-1-015301, author = "Nzar Rauf Abdullah and Chi-Shung Tang and Andrei Manolescu and Vidar Gudmundsson", title = "Coherent transient transport of interacting electrons through a quantum waveguide switch", journal = "Journal of Physics: Condensed Matter", volume = 27, number = 1, pages = 015301, url = "http://stacks.iop.org/0953-8984/27/i=1/a=015301", year = 2015, arxiv = "http://arxiv.org/abs/1408.1007", doi = "10.1088/0953-8984/27/1/015301", abstract = "We investigate coherent electron-switching transport in a double quantum waveguide system in a perpendicular static or vanishing magnetic field. The finite symmetric double waveguide is connected to two semi-infinite leads from both ends. The double waveguide can be defined as two parallel finite quantum wires or waveguides coupled via a window to facilitate coherent electron inter-wire transport. By tuning the length of the coupling window, we observe oscillations in the net charge current and a maximum electron conductance for the energy levels of the two waveguides in resonance. The importance of the mutual Coulomb interaction between the electrons and the influence of two-electron states is clarified by comparing results with and without the interaction. Even though the Coulomb interaction can lift two-electron states out of the group of active transport states the length of the coupling window can be tuned to locate two very distinct transport modes in the system in the late transient regime before the onset of a steady state. A static external magnetic field and quantum-dots formed by side gates (side quantum dots) can be used to enhance the inter-waveguide transport which can serve to implement a quantum logic device. The fact that the device can be operated in the transient regime can be used to enhance its speed." }