Electronic Structure of CdS Nanoparticles and CdSe/CdS Nanosystems

The electronic states of “wurtzite” CdS nanoparticles and CdSe/CdS nanosystems with up to 80 pairs of Cd-Se or CdS atoms were calculated.The results for CdS particles were compared with the results obtained earlier for CdSe particles of the same size and with published calculations of other authors. The calculated gap values in the range of 2.84 eV ~ 3.78 eV are typical for CdS particles of studied sizes in accordance with results of published data. The CdSe/CdS nanosystems were considered as layered ones and as quantum dots. The layered CdSe/CdS systems with twolayer CdS coverings can be interpreted in terms of combinations of two semiconductors with different energy band gaps (2.6 eV and 3.3 eV), while analogous systems with single-layer CdS coverings do not demonstrate a two-gap electron structure. Simulation of a CdSe/CdS quantum dot shows that the single-layer CdS shell demonstrates a tendency for the formation of the electronic structure with two energy gaps: approximately of 2.5 eV and 3.0 eV

Specific heat of MgB2_2 in a one- and a two-band model from first-principles calculations

The heat capacity anomaly at the transition to superconductivity of the layered superconductor MgB$_2$ is compared to first-principles calculations with the Coulomb repulsion, $\mu^\ast$, as the only parameter which is fixed to give the measured $T_c$. We solve the Eliashberg equations for both an isotropic one-band and a two-band model with different superconducting gaps on the $\pi$ and $\sigma$ Fermi surfaces. The agreement with experiments is considerably better for the two-band model than for the one-band model.Comment: final published versio

Infrared and optical spectroscopy of alpha and gamma-phase Ce

We determined the optical properties of alpha- and gamma-phase Ce in the photon energy range from 60 meV to 2.5 eV using ellipsometry and grazing incidence reflectometry. We observe significant changes of the optical conductivity, the dynamical scattering rate, and the effective mass between alpha- and gamma-cerium. The alpha-phase is characterized by Fermi-liquid frequency dependent scattering rate, and an effective mass of about 20 m_e on an energy scale of about 0.2 eV. In gamma-Ce the charge carriers have a large scattering rate in the far infrared, and a carrier mass characteristic of 5d band electrons. In addition we observe a prominent absorption feature in alpha-Ce, which is absent in gamma-Ce, indicating significant differences of the electronic structure between the two phases.Comment: 5 pages, REVTeX, 2 eps-figures, Phys.Rev.Lett., in pres