Controlled Coulomb effects in core-shell quantum rings

We analyse theoretically the possibilities of contactless control of in-gap states formed by a pair of electrons confined in a triangular quantum ring. The in-gap states are corner-localized states associated with two electrons occupying the same corner area, and thus shifted to much higher energies than other corner states, but still they are below the energies of corner-side-localized states. We show how the energies, degeneracy and splittings between consecutive levels change with the orientation of an external electric field relatively to the polygonal cross section. We also show how absorption changes in the presence of external electric and magnetic fields.Comment: 4 pages, 2 figure

Excitons in core-shell nanowires with polygonal cross sections

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 multi-electron numerical approach based on the exact solution of the multi-particle 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 multi-electron 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.This work was supported by the Icelandic Research Fun

Electronic and optical properties of semiconductor nanowires with prismatic geometry

In this work, fundamental electronic and optical properties of semiconductor prismatic nanowires, which are a direct consequence of their geometry, are numerically studied. The quantum states of electrons confined in polygonal shells, which describe the cross-section of nanowires where a conducting shell surrounds an insulating core, are obtained using a finite-elements method based on a polar grid, which allows to model a wide range of different shapes. Directly related with the quantum states of the nanowires, the charge and current distributions, conductance and excitonic states are obtained using several computational models. The light scattering by prismatic nanowires is also studied by solving Maxwell’s equations with the finite elements method built in the software COMSOL Multiphysics. The results presented here demonstrate that the specific geometry of such nanowires is a source of rich and interesting phenomenology.Í þessu verki eru raf- og ljósfræðilegir eiginleikar hálfleiðandi nanóvíra út frá úmfræði þeirra, rannsakaðir með tölulegum reikningum. Skammtafræðileg ástönd rafeinda í strendingslaga hvelum, sem lýsa þverskurði nanóvírana með leiðandi skel umhverfis einangrandi kjarna, eru reiknuð með bútaaðferð á neti í pólhnitum. Hleðslu- og straum þéttleiki ásamt leiðni og örveinda ástöndum, sem eru beintengd skammtaástöndum nanóvíra, eru fengin með fleiri en einu tölvulíkani. Ljósdreifing strendingslaga nanóvíra er að auki skoðuð með lausnum Maxwells jafna með bútaaðferð hugbúnaðisins COMSOL Multiphysics. Niðurstöður sýna að rúmfræðilega lögun nanóvíra er rík uppspretta áhugaverðar eðlisfræði