Dielectric confinement of excitons in type-I and type-II semiconductor nanorods

We theoretically study the effect of the dielectric environment on the exciton ground state of CdSe and CdTe/CdSe/CdTe nanorods. We show that insulating environments enhance the exciton recombination rate and blueshift the emission peak by tens of meV. These effects are particularly pronounced for type-II nanorods. In these structures, the dielectric confinement may even modify the spatial distribution of electron and hole charges. A critical electric field is required to separate electrons from holes, whose value increases with the insulating strength of the surroundings.Comment: Journal of Physics: Condensed Matter (in press

Magnetic modulation of the tunneling between defects states in antidot superlattices

We show theoretically that the tunnelling between properly designed defects in periodic antidot lattices can be strongly modulated by applied magnetic fields. Further, transport channels made up of linear arrangements of tunnel-coupled defects can accommodate Aharonov-Bohm cages, suggesting a magnetic control of the transport through the system. Evidence supporting an unusual robustness of the caging effect against electron-electron interactions is also provided

Two-dimensional Bloch electrons under strong magnetic modulation

The band structure of a high-mobility two-dimensional electron gas patterned with a square lattice of holes (antidots) is studied theoretically under the influence of a magnetic modulation consisting of perpendicular magnetic flux tubes with the same period and nonzero net flux per unit cell. The magnetic field pierces the system through the patterned holes only, so that the coupling with the electrons is purely quantum mechanical. The model takes implicitly into account the coupling between the different Bloch bands. The flux-dependent energy structure exhibits a Hofstadter butterfly-type spectrum. Such a structure is repeated indefinitely without distortion with a period of one magnetic flux quantum through a lattice hole. Rectangular deviations from the square lattice are also studied. It is found that the number and width of the magnetic gaps decrease, and even disappear for large antidot filling fractions

Theory of electrons, holes and excitons in GaAs polytype quantum dots

Single and multi-band (Burt-Foreman) k.p Hamiltonians for GaAs crystal phase quantum dots are developed and used to assess ongoing experimental activity on the role of such factors as quantum confinement, spontaneous polarization, valence band mixing and exciton Coulomb interaction. Spontaneous polarization is found to be a dominating term. Together with the control of dot thickness [Vainorious Nano Lett. 15, 2652 (2015)] it enables wide exciton wavelength and lifetime tunability. Several new phenomena are predicted for small diameter dots [Loitsch et al. Adv. Mater. 27, 2195 (2015)], including non-heavy hole ground state, strong hole spin admixture and a type-II to type-I exciton transition, which can be used to improve the absorption strength and reduce the radiative lifetime of GaAs polytypes

Emission spectrum of quasi-resonant laterally coupled quantum dots

We calculate the emission spectrum of neutral and charged excitons in a pair of laterally coupled InGaAs quantum dots with nearly degenerate energy levels. As the interdot distance decreases, a number of changes take place in the emission spectrum which can be used as indications of molecular coupling. These signatures ensue from the stronger tunnel-coupling of trions as compared to that of neutral excitons.Comment: 7 pages, 7 figure

Magnetic field dependence of hole levels in self-assembled InAs quantum dots

Recent magneto-transport experiments of holes in InGaAs quantum dots [D. Reuter, P. Kailuweit, A.D. Wieck, U. Zeitler, O. Wibbelhoff, C. Meier, A. Lorke, and J.C. Maan, Phys. Rev. Lett. 94, 026808 (2005)] are interpreted by employing a multi-band kp Hamiltonian, which considers the interaction between heavy hole and light hole subbands explicitely. No need of invoking an incomplete energy shell filling is required within this model. The crucial role we ascribe to the heavy hole-light hole interaction is further supported by one-band local-spin-density functional calculations, which show that Coulomb interactions do not induce any incomplete hole shell filling and therefore cannot account for the experimental magnetic field dispersion.Comment: 5 pages with 3 figures and one table. The paper has been submitted to Phys.Rev.

On the role of AGN feedback on the thermal and chemodynamical properties of the hot intra-cluster medium

We present an analysis of the properties of the ICM in an extended set of cosmological hydrodynamical simulations of galaxy clusters and groups performed with the TreePM+SPH GADGET-3 code. Besides a set of non-radiative simulations, we carried out two sets of simulations including radiative cooling, star formation, metal enrichment and feedback from supernovae, one of which also accounts for the effect of feedback from AGN resulting from gas accretion onto super-massive black holes. These simulations are analysed with the aim of studying the relative role played by SN and AGN feedback on the general properties of the diffuse hot baryons in galaxy clusters and groups: scaling relations, temperature, entropy and pressure radial profiles, and ICM chemical enrichment. We find that simulations including AGN feedback produce scaling relations that are in good agreement with X-ray observations at all mass scales. However, our simulations are not able to account for the observed diversity between CC and NCC clusters: unlike for observations, we find that temperature and entropy profiles of relaxed and unrelaxed clusters are quite similar and resemble more the observed behaviour of NCC clusters. As for the pattern of metal enrichment, we find that an enhanced level of iron abundance is produced by AGN feedback with respect to the case of purely SN feedback. As a result, while simulations including AGN produce values of iron abundance in groups in agreement with observations, they over-enrich the ICM in massive clusters. The efficiency of AGN feedback in displacing enriched gas from halos into the inter-galactic medium at high redshift also creates a widespread enrichment in the outskirts of clusters and produces profiles of iron abundance whose slope is in better agreement with observations.Comment: 23 pages, 14 figures, 1 table, accepted for publication in MNRA

Generalized method of image dyons for quasi-two dimensional slabs with ordinary - topological insulator interfaces

Electrostatic charges near the interface between topological (TI) and ordinary (OI) insulators induce magnetic fields in the medium that can be described through the so-called method of image dyons (electric charge - magnetic monopole pairs), the magnetoelectric extension of the method of image charges in classical electrostatics. Here, we provide the expressions for the image dyons and ensuing magnetoelectric potentials in a system comprised by two planar-parallel OI-TI interfaces conforming a finite-width slab. The obtained formulae extend earlier work in that they account for all different combinations of materials forming the slab and its surroundings, including asymmetric systems, as well as all possible combinations of external magnetization orientations on the interfaces. The equations are susceptible of implementation in simple computational codes, to be solved recurrently, in order to model magnetoelectric fields in topological quantum wells, thin films, or layers of two-dimensional materials. We exemplify this by calculating the magnetic fields induced by a point charge in nanometer-thick quantum wells, by means of a Mathematica code made available in repositories.Funding for open access charge: CRUE-Universitat Jaume

Delocalized image surface states in defects free SiO2 hollow nanospheres

Delocalized image surface states in free-standing hollow silica nanospheres populated with one or two electrons or an exciton are theoretically predicted for a wide range of internal radii and shell thicknesses. The driving force building up these surface states is the image self-polarization potential originating from the dielectric mismatch between the nanoshell and the surrounding air. The surface states are localized in a spherical crown beyond the nanoshell border. The transition from volume to surface state will then have to overcome the spatial confining potential barrier of the nanoshell. Owing to the different spatial confining barriers of electrons and holes in the silica nanoshell, electron but no hole density can be concentrated in surface distributions. The self-polarization potential looks like a double well potential, each well located just beyond the nanoshell border, with the internal well deeper than the external one, so that an excess carrier is attracted more strongly by the inner interface. This leads the electron density of a surface state to be located mainly in the internal surface of the hollow nanosphere. The shorter the inner nanoshell radius is, the stronger the binding of the excess electron to the surface will be. The volume/surface ground state phase diagrams of the one-electron, two-electron, and exciton systems have been calculated. All three diagrams are quite similar, thus revealing the monoelectronic character of the driving force for the transition from volume to surface state