arXiv subjects

Kristjan Ottar Klausen

Publications and source records attributed to Kristjan Ottar Klausen.

7 recordsLinked to original sources

arXiv2023

Flux-periodic oscillations in proximitized core-shell nanowires

Flux-periodic oscillations of the superconducting gap in proximitized core-shell nanowires are explored. Periodicity of oscillations in the energy spectrum of a cylindrical nanowire is compared with nanowires having hexagonal and square cross-section geometry, along with the effects of Zeeman and Rashba spin-orbit interaction. A transition between h/e and h/2e periodicity is found and shown to be dependent on the chemical potential, with correspondence to degeneracy points of the angular momentum quantum number. For a thin shell of a square nanowire, solely h/e periodicity is found in the infinite wire spectrum and shown to result from energy separation between the lowest groups of excited states.

cond-mat.mes-hall↗

arXiv2023

Electron-hole coherence in core-shell nanowires with partial proximity induced superconductivity

By solving the Bogoliubov-de Gennes Hamiltonian, the electron-hole coherence within a partially proximitized n-doped semiconductor shell of a core-shell nanowire heterostructure is investigated numerically and compared with the Andreev reflection interpretation of proximity induced superconductivity. Partial proximitization is considered to quantify the effects of a reduced coherence length. Three cases of partial proximitization of the shell are explored: radial, angular and longitudinal. For the radial case, it is found that the boundary conditions impose localization probability maxima in the center of the shell in spite of off-center radial proximitization. The induced superconductivity gap is calculated as a function of the ratio between the proximitized shell thickness and the total shell thickness. In the angular case, the lowest energy state of a hexagonal wire with a single proximitized side is found to display the essence of Andreev reflection, only by lengthwise summation of the localization probability. In the longitudinal case, a clear correspondence with Andreev reflection is seen in the localization probability as a function of length along a half-proximitized wire. The effect of an external magnetic field oriented along the wire is explored.

cond-mat.mes-hall↗

arXiv2023

Visualizing Stokes' theorem with Geometric Algebra

Foundational cases of the generalized Stokes' theorem are visualized using geometric algebra. From considering bivector valued fields, two seldom used instances of the theorem are obtained. Graphical representations are given, showing a radial spin structure corresponding to the generalized curl and a toroidal vortex for the generalized divergence. Dualities and applications to natural phenomena with non-trivial topology are discussed.

math.GM↗

arXiv2023

Effect of Impurities on Charge and Heat Transport in Tubular Nanowires

We calculate the charge and heat currents carried by electrons, originating from a temperature gradient and a chemical potential difference between the two ends of tubular nanowires with different geometries of the cross-sectional areas: circular, square, triangular, and hexagonal. We consider nanowires based on InAs semiconductor material, and use the Landauer-Büttiker approach to calculate the transport quantities. We include impurities in the form of delta scatterers and compare their effect for different geometries. The results depend on the quantum localization of the electrons along the edges of the tubular prismatic shell. For example, the effect of impurities on the charge and heat transport is weaker in the triangular shell than in the hexagonal shell, and the thermoelectric current in the triangular case is several times larger than in the hexagonal case, for the same temperature gradient.

cond-mat.mes-hall↗

arXiv2023

Charge and heat currents in prismatic tubular nanowires

We calculate electronic charge and heat transport in tubular nanowires generated by a temperature gradient or a chemical potential bias. These nanowires correspond to semiconductor core-shell nanowires with insulating (undoped) core and conductive (doped) shell, such that the conduction takes place only in the shell. The cross section of such nanowires is typically polygonal. We study the influence of the cross section shape and shell thickness on the electric and heat conduction of the shell. We use the Landauer-Büttiker approach to calculate the electric and heat currents as a non-linear function of temperature and chemical potential bias beyond the linear regime.

cond-mat.mes-hall↗

arXiv2021

Electromagnetic field emitted by core-shell semiconductor nanowires driven by an alternating current

We consider tubular nanowires with a polygonal cross-section. In this geometry the lowest energy states are separated in two sets, one of corner and one of side-localized states, respectively. The presence of an external magnetic field transverse to the nanowire imposes an additional localization mechanism, the electrons being pushed sideways relatively to the direction of the field. This effect has important implications on the current density, as it creates current loops induced by the Lorentz force. We calculate numerically the electromagnetic field radiated by hexagonal, square, and triangular nanowires. We demonstrate that, because of the aforementioned localization properties, the radiated field can have a complex distribution determined by the internal geometry of the nanowire. We suggest that measuring the field in the neighborhood of the nanowire could be the basic idea of a tomography of the electron distribution inside it, if a smaller receiver antenna could be placed in that zone.

cond-mat.mes-hall↗

arXiv2020

Majorana Zero Modes in Nanowires with Combined Triangular and Hexagonal Geometry

The effects of geometry on the hosting of Majorana zero modes are explored in core-shell nanowires with a hexagonal core and a triangular shell, and vice versa. The energy interval separating electronic states localized in the corners from states localized on the sides of the shell is shown to be larger for a triangular nanowire with a hexagonal core, than a triangular one. We build the topological phase diagram for both cases and compare them to earlier work on prismatic nanowires with the same core and shell geometry. We suggest that a dual core nanowire is needed to allow for a braiding operation of Majorana zero modes at the nanowire end plane.

cond-mat.mes-hall↗