Jian-Qing Wang

A study of the transport properties and the annealing effect in Nd1.86Ce0.14CuO4+δ single crystal

The in-plane resistivity (ρ) and thermopower (S) were measured on Nd1.86Ce0.14CuO4+δ single crystal after different annealing times. Both S and ρ can be described in terms of a two-band model with an electron broad band and a hole-like narrow band. From ρ and S data, we found that the hole component increases with the annealing time before the optimal superconductivity is achieved, while S and ρ reach saturation after further annealing in N2. So the annealing process has the same effect as Ce doping just before the sample is optimally annealed, while after that they are not equal to each other. Furthermore, we also argue that the holes may be responsible for the superconductivity in the electron-doped cuprates.

Intervalley Γ-X Deformation Potentials in III-V Zincblende and Si Semiconductors by Ab Initio Pseudopotential Calculations

Intervalley Γ-X deformation potential constants (IVDPs) have been calculated by first principle pseudopotential method for the III-V zincblende semiconductors A1p, A1As, A1Sb, Gap, GaAs, GaSb, InP, InAs and InSb. As a prototype crystal we have also carried out calculations on Si. When comparing the calculated IVDPs of LA phonon for Gap, InP and InAs and LO phonon for A1As, A1Sb, GaAs, GaSb and InSb with a previous calculation by EPM in rigid approximation, good agreements are found. However, our ab initio pseudopotential results of LA phonon for A1As, A1Sb, GaAs, GaSb and InSb and LO phonon for Gap, InP and ZnAs are about one order of magnitude smaller than those obtained by EPM calculations, which indicate that the electron redistributions upon the phonon deformations may be important in affecting Γ-X intervalley shatterings for these phonon modes when the anions are being displaced. In our calculations the phonon modes of LA and LO at X point have been evaluated in frozen phonon approximation. We have obtained, at the same time, the LAX and LOX phonon frequencies for these materials from total energy calculations. The calculated phonon frequencies agree very well with experimental values for these semiconductors.

First principles pseudopotential calculations of zone boundary phonon frequencies of III-V zincblende semiconductors

Abstract Longitudinal zone boundary X phonon frequencies have been calculated by a first principles pseudopotential method for III-V zincblende semiconductors AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs and InSb. The phonon frequencies have been evaluated from total energy calculations in the frozen phonon approximation. The calculated phonon frequencies agree very well with the experimental values.