Koichi Shindo

Electronic Structure of Black Phosphorus in Self-Consistent Pseudopotential Approach

The energy band structure of black phosphorus is calculated by using self-consistent pseudopotential method. The resulting band structure has the direct minimum gap at the point Z in the Brillouin zone in agreement with the result of the tight-binding approach. Effective electron and hole masses and the level shift of the band edge by pressure are calculated from the bands obtained. The pressure dependence of the energy gap is in good agreement with experiment, but the anisotropy of the effective masses contradicts that of the electrical conductivity measured for the single crystal. The nature of the optical absorption edge is discussed in terms of the calculated band structure.

Spin-Orbit Coupling in Ionic Crystals with Zincblende and Wurtzite Structures

The spin-orbit couplings in the valence bands of the zincblende and wurtzite structures such as cuprous halides and ZnO are investivigated in the tight-binding approximation. It is shown that the d-orbital of the cation contributes a negative term to the spin-orbit coupling in the valence band at k =0 in these compounds and, as a result of it, the spin-orbit splittings in the valence bands of CuCl and ZnO are inverted.

Effective Electron-Hole Interaction in Shallow Excitons

The Greens function method developed by Mahan for excitons is extended to the case that the interaction is not instantaneous. Energy corrections to the exciton due to recoil effects, retardation effects, renormalization constants and vertex parts arising from the interactions of an electron and a hole forming an exciton with longitudinal optical (LO) phonons, which were treated by Haken in another simplified manner, are explicitly calculated by using the extended method to first order in electron-phonon coupling constant α and in (\(E/\hbar\omega_{l}\)), where E is the binding energy of the exciton and ω l is the LO phonon frequency. It is shown that in these corrections, the recoil effect and the retardation effect cancel out each other and the renormalization effect and the vertex effect cancel out each other, and a resultant effective interaction between the electron and hole is reduced to Hakens result for large electron-hole separations.

The Effective Mass Equation for the Multi-Valley Semiconductors

The validity of the multivalley effective mass equation which has been conventionally used by many authors is examined. It is shown that the equation will not describe the intervalley mixing properly. An alternative equation which replaces the conventional equation is derived and discussed. Essential features of the new equation are: the lack of the intervalley mixing via kinetic energy, and the modification of impurity potential by the product of the periodic parts of the Bloch functions at the conduction band minima. Importance of the effect of anisotropy of the effective mass is discussed.

Exciton-L0 Phonon Scattering in Cu2O

Reliable absorption line shape of the several higher members of the yellow exciton series in Cu 2 O has been measured by the photoelectric method using a monochromator with a large dispersion at 1.8 K, and has been analyzed on the basis of Toyozawas formula. The origin of the half width is considered to come from the interband scattering of the exciton from the p state to the 1 s state by the two modes of L0 phonons. The estimated ratio in the line width of the n -th member to the second member of the exciton series is in agreement with the experimental one.

The band structure of solid iodine under pressure and the mechanism of the pressure-induced insulator-to-metal transition

The band structures of solid iodine under ambient pressure and 15.3 GPa were calculated with the ab initio pseudopotential method. The apparently complicated band structures have been resolved by a detailed analysis, revealing the mechanism of the band overlap which causes the pressure-induced insulator-to-metal transition: The interlayer interaction as well as the interaction between the third-nearest neighbor atoms is responsible for the band overlap. The effect of the spin-orbit interaction on the band overlap is also discussed

Band structure and structural stability of the high-pressure phases of the group VIb elements

Abstract The group VIb elements, such as sulfur, selenium and tellurium, exhibit similar successive structural phase transitions under pressure. The electronic band-structure of the high-pressure phases of these elements is investigated on the basis of first principles calculation. In particular, the structural stability of the β-Po type rhombohedral phase of selenium has been studied, and the result suggests that the rhombohedral structure becomes unstable owing to monoclinic distortion.

Structural stability and band structure of the metallic phase of phosphorus

The total energies of the rhombohedral A7 and the simple cubic (SC) phases of phosphorus are calculated within the local-density-functional formalism by using the norm-conserving pseudopotential. The calculated results successfully explain the phase transition from the A7 phase to the SC one under pressure. The calculated electronic structure of the metallic SC phase reveals that the bonding in this phase has an appreciable amount of covalency. It is also found that the stabilization of the SC structure under high pressure is due to be fact that the contribution of the electrostatic energy to the total energy increases on the compression. Moreover, it is shown that the absence of the core d -orbitals of a phosphorus atom is very important in explaining the difference between phosphorus and other VB-elements in the phase transition under pressure.

A Pseudopotential Approach to the Crystal Energy of Si

The pseudopotential of Si crystal is determined self-consistently from the Topp-Hopfield type model potential of Si atom by using the Slater approximation. The crystal energy and compressibility are calculated on the basis of the resultant band structure and the charge density. A good agreement between the calculated values and the experimental ones is obtained with no adjustment such as the zero pressure condition nor fitting to the band structure near the fundamental band gap as done in the usual empirical pseudopotential methods.

Structural phase transitions and equations of state of Se and Te under high pressure

Selenium and tellurium are known to undergo several structural phase transitions under pressure. We have investigated the band-structures and the total energies of β-P 0 type (rhombohedral) structure and body-centered cubic structure of Se and Te within the local density-functional formalism using the norm-conserving pseudopotential method. The calculated equations of state are in good agreement with the experimental ones. We also discuss the structural stability of the high pressure phases