I outline a modern theory of the macroscopic polarization P in crystalline dielectrics. While P itself is not an observable, the polarization difference ΔP between any two crystal states can be measured, defined and calculated as a bulk material property: the root of this fact lies in a geometric quantum phase. In general, ΔP cannot be recovered from periodic charge densities, where any phase information is deleted: dielectric polarization is in fact a quantum phenomenon, governed by a gauge-invariant phase feature of the crystal wave functions.

https://iopscience.iop.org/article/10.1209/0295-5075/22/2/010/pdf

Macroscopic electric polarization as a geometric quantum phase

The temperature dependence of the long-wavelength optical phonons of $3C$-type SiC has been measured for temperatures up to 750 K. The LO-TO splitting diminishes with increasing temperature. From these data a weak decrease of the transverse effective charge with increasing temperature is also derived. The "explicit" temperature contribution to the variation of the transverse effective charge is determined experimentally and calculated in terms of a pseudopotential expression for the charge. Good agreement between theory and experiment is achieved.

Temperature dependence of the optical phonons and transverse effective charge in 3 C -SiC

Theoretical investigations of the electronic, optical and elastic properties of cadmium and zinc chalcogenides in the zinc-blende structure are performed using a pseudopotential formalism. Our results are in reasonable agreement with the available experimental data. Polynomial expressions are obtained for the electron effective mass and the static dielectric constant as a function of the fundamental energy band-gap. Relations of elastic constants ratio to the ionicity are also examined and discussed.

Band parameters for cadmium and zinc chalcogenide compounds

The angular dependence of flux, mean energy and speed ratio for D2 molecules desorbing from a Ni(111) surface

We report on Raman spectroscopy study of hexagonal InN thin films grown by metal-organic vapor-phase epitaxy, with the emphasis on frequencies and linewidths of E2(high) and A1(LO) modes in the temperature range from 93to443K The present InN exhibits a fundamental band gap of ∼12eV from photoluminescence and optical transmission spectra, which is in good agreement with the recent suggested parameter for intrinsic InN The temperature dependence of the E2(high) and A1(LO) phonons can be described well by a model which has taken into account the contributions of the thermal expansion of the crystal lattice, the strain between InN thin films and sapphire substrates, as well as three- and four-phonon coupling Micro-Raman mapping results also demonstrate the high uniformity of the studied InN

Temperature dependence of Raman scattering in hexagonal indium nitride films

A method for an ab-initio calculation of transverse dynamical effective charges Z* in partially covalent semiconductors within the framework of pseudopotential theory is presented. It is based on previously established expressions for Z* in terms of the inverse microscopic dielectric function of the crystal but circumvents the direct inversion of the latter. In contrast to earlier calculations the results are definitely boundary insensitive. Moreover, the acoustic sum rule expressing charge neutrality is inherently guaranteed. Within the local empirical pseudopotential method a simple analytical model calculation, which is compared with the bond orbital model, as well as a full numerical computation is performed. For III-V compounds the resulting Z* underestimate the experimental effective charges by approximately 30% while good agreement for II-VI materials is obtained. Reasons for these findings are discussed and the effects of several refinements are estimated.

https://iopscience.iop.org/article/10.1088/0022-3719/11/2/011/pdf

P Vogl

Papers

Dynamical effective charges in semiconductors: A pseudopotential approach