Topological suppression of magnetoconductance oscillations in NS junctions

We show that the magnetoconductance oscillations of laterally-confined 2D NS junctions are completely suppressed when the superconductor side enters a topological phase. This suppression can be attributed to the modification of the vortex structure of local currents at the junction caused by the topological transition of the superconductor. The two regimes (with and without oscillations) could be seen in a semiconductor 2D junction with a cleaved-edge geometry, one of the junction arms having proximitized superconductivity. We predict similar oscillations and suppression as a function of the Rashba coupling. The oscillation suppression is robust against differences in chemical potential and phases of lateral superconductors.Comment: 7 pages, 7 figure

Conductance oscillations and speed of chiral Majorana mode in a quantum-anomalous-Hall 2d strip

We predict conductance oscillations in a quantum-anomalous Hall 2d strip having a superconducting region of length $L_x$ with a chiral Majorana mode. These oscillations require a finite transverse extension of the strip $L_y$ of a few microns or less. Measuring the conductance periodicity with $L_x$ and a fixed bias, or with bias and a fixed $L_x$, yields the speed of the chiral Majorana mode. The physical mechanism behind the oscillations is the interference between backscattered chiral modes from second to first interface of the NSN double junction. The interferometer effect is enhanced by the presence of side barriers.Comment: 9 pages, 9 figures. Added references. Added Supplemental Material results. Published versio

Magnetic Thomas-Fermi-Weizs\"acker model for quantum dots: a comparison with Kohn-Sham ground states

The magnetic extension of the Thomas-Fermi-Weizs\"acker kinetic energy is used within density-functional-theory to numerically obtain the ground state densities and energies of two-dimensional quantum dots. The results are thoroughly compared with the microscopic Kohn-Sham ones in order to assess the validity of the semiclassical method. Circular as well as deformed systems are considered.Comment: EPJ LateX, revised EPJ-

Majorana states and magnetic orbital motion in planar hybrid nanowires

The Majorana phase boundaries in planar 2D hybrid (semiconductor-superconductor) nanowires are modified by orbital effects due to off plane magnetic components. We show that Majorana zero modes survive sizable vertical field tiltings, uncovering a remarkable phase diagram. Analytical expressions of the phase boundaries are given for the strong orbital limit. These phase boundaries can be fulfilled with attainable setups, such as an InAs nanowire of $150\, {\rm nm}$ in transverse width.Comment: 9 pages, 6 figures. ( Only acknowledgement update

Electromagnetic absorption of quasi-1D Majorana nanowires

We calculate the electromagnetic absorption cross section of long and narrow nanowires, in the so-called quasi-1D limit. We consider only two transverse bands and compute the dipole absorption cross section taking into account quasiparticle transitions from negative to positive energy eigenstates of the Bogoliubov-de Gennes Hamiltonian. The presence of the zero energy (Majorana) state manifests in the different absorption spectra for $x$ (parallel) and $y$ (transverse) polarizations of the electromagnetic field. In the $y$-polarized case, the Majorana state causes a low energy absorption plateau extending from mid-gap up to full-gap energy. Increasing further the energy, the plateau is followed by a region of enhanced absorption due to transitions across the full gap. For $x$ polarization the low energy absorption plateau is not observed.Comment: Submitted to E-MRS Spring Meeting 2015 ( Only acknowledgement update

A scattering model of 1D quantum wire regular polygons

We calculate the quantum states of regular polygons made of 1D quantum wires treating each polygon vertex as a scatterer. The vertex scattering matrix is analytically obtained from the model of a circular bend of a given angle of a 2D nanowire. In the single mode limit the spectrum is classified in doublets of vanishing circulation, twofold split by the small vertex reflection, and singlets with circulation degeneracy. Simple analytic expressions of the energy eigenvalues are given. It is shown how each polygon is characterized by a specific spectrum.Comment: 8 pages, 5 figure

Spin-orbit coupling and the electronic properties of quantum wires

En aquest treball es revisen diversos resultats recents sobre la importància de la interacció espín-òrbita de Rashba per a l'estructura electrònica i la conductància de cables quàntics. Primerament es comenta com l'acoblament entre subbandes donat per la interacció de Rashba és crucial per a les energies de subbanda i les distribucions espacials d'espins, especialment en presència de camps magnètics. A continuació considerem el càlcul dels modes evanescents d'un cable quàntic, remarcant les peculiaritats degudes a la interacció d'espín-òrbita. Finalment, considerem el cas d'una interacció de Rashba localitzada, on fem la predicció de fortes ressonàncies de tipus Fano a la dependència de la conductància amb l'energia de l'electró incident. Aquestes ressonàncies s'observen més clarament a les transmissions de cada espín per separat. Trobem resultats numèrics exactes amb l'algorisme de frontera transmissora quàntica i resultats analítics amb un model simplificat de clara interpretació física.We review recent work on the effects of the Rashba spin-orbit interaction on the electronic structure and the conductance of quantum wires. We first discuss the importance of the intersubband coupling induced by the Rashba interaction for the wire subband-energies and spin distributions, especially in the presence of in-plane magnetic fields. We then consider the calculation of the evanescent modes, emphasizing the peculiarities of these states in the presence of spin-orbit coupling. Finally, we discuss the physical effects of a localized Rashba interaction in a quantum wire. We predict in this case the occurrence of Fano resonances in the dependence of the wire conductance with the incident electron energy. The Fano lineshapes manifest themselves more clearly in the spin-resolved transmissions. We obtain exact numerical results within the quantum-transmittingboundary algorithm and also propose a simplified approach (the coupled-channel model) that captures the main ingredients of the effect and allows a more transparent physical interpretation