The Zeeman splitting of the valence band of a cubic Cr-based diluted magnetic semiconductor is studied within an effective Hamiltonian for the hybridization-induced hole-ion interaction that includes orbital coupling terms. The static Jahn-Teller distortion tends to quench the orbital contribution. The subband ordering is the same as in the Kondo-like spin-exchange model, but the overall splitting is reduced. We also compute the magnetization. Comparison with recently published magnetoreflectance and magnetization data in ${\mathrm{Zn}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Cr}}_{\mathit{x}}$Se shows excellent agreement. The anomalous sign (ferromagnetic) of the effective p-d exchange is explained.

We investigate theoretically the effect of the warped and nonparabolic valence-band structure on the total scattering rates for holes in cubic semiconductors with diamond lattices using the multiband effective-mass theory. All numerical calculations are done for silicon and include ionized-impurity scattering, optical-, and acoustical-phonon scattering. We find that the anisotropy and nonparabolicity of the valence bands result in a considerable dependence of the total scattering rates on the incident direction of the hole wave vector.

Time-resolved local voltage profiling in semi-insulating GaAs by electro-optics shows spontaneous current oscillations being caused both by contact domains and propagating domains in the bulk. In particular, we prove that the critical electric fields in the bulk are much higher than the average field inferred from geometry and exceed the threshold field for the Gunn effect. The dynamics of domain propagation are governed by the interaction between two different oscillatory systems, namely the contact region and bulk GaAs.

When the interlayer separation is not large, the ground state of a double layer of two-dimensional electron fluids in a large magnetic field is determined by correlations arising from the interlayer Coulomb repulsion. We suggest that, as a consequence, the independent translational invariance of the electrons in each layer is lost, independent of the filling fraction of the Landau levels. The gap measured recently in tunneling across the bilayer is explained and experiments are proposed to test our description.

The bonding at O (N) atom-terminated dangling bonds at steps in the 112¯ direction is investigated by ab initio cluster calculations. We find that one Si atom and three O (N) atoms, i.e., a ${\mathrm{SiO}}_3$ (${\mathrm{SiN}}_3$) group, can bridge three dangling bonds such that the strain induced at the step by these bonding groups is negligible. The results help to explain the significant changes in the interface trap density ${\mathit{D}}_{\mathrm{it}}$ and the relative phase of the onefold and threefold contributions to the second-harmonic generation from oxide-terminated vicinal Si surfaces formed by thermal oxidation at 850 °C following annealing at temperatures ∼1000 °C, where Si-O atom arrangements can readily occur.

We derive a relationship between the nonequilibrium particle distribution function and the scattering distribution function with nonlocal self-energy due to random impurity scattering. Using this relationship, we obtain a transport equation for mesoscopic devices that contains both known and random elastic scatterers. We show that for arbitrary applied bias, our equation resembles Büttiker’s equation for coherent transport with continuous voltage probes.

Spin-orbit coupling of electron motion in a one-dimensional conducting ring is examined with a confining potential to keep the electron path exactly in a circle. It is found that a non-symmetrical potential is essential for the onset of spin-orbit coupling. This result may be useful for understanding some mesoscopic phenomena, e.g., persistent currents.

The Hall potential distribution and the current distribution in long Hall-bar samples are calculated by considering explicitly the presence of sample edges. We distinguish edge currents from bulk currents to determine the fraction of edge currents.

The transition from two peaks of unit height to a single peak, with height less than one, in the transmission coefficient T of symmetrical triple-barrier resonant structures, as the width of the central barrier is increased, is analyzed in terms of a resonance formalism in a Breit-Wigner fashion to show that the above siutation is due to strong overlap between the two resonance states of the corresponding miniband, the condition for this being (${\mathrm{\epsilon }}_2$-${\mathrm{\epsilon }}_1$)≤[${\mathrm{\Gamma }}_1$${\mathrm{\Gamma }}_2$${]}^{1/2}$. We also discuss the implications of strong overlap on the current-voltage characteristics of these triple-barrier structures.

The optical properties of (113)-oriented GaAs/AlAs superlattices grown by atomic-layer molecular-beam epitaxy at low substrate temperature have been studied by means of piezoreflectance techniques. Several transitions have been detected which exhibit heavy-hole and light-hole character. The heavy-hole transitions are more polarized along the [33¯2] direction whereas the light-hole transitions are more polarized along the [1¯10] direction. We have also performed calculations for these superlattices by using an empirical tight-binding Hamiltonian. According to the results thus obtained the observed optical anisotropy is related to the different components of the valence-band wave functions of the superlattices.

An asymptotic solution for light-induced exciton density oscillations in a semiconductor is calculated from the semiconductor Bloch equations in the low density limit (weak optical excitation). The analytic approximation is compared with a numerical solution of the full equations. It is shown that even for low area fields (≪2π) density oscillations are caused by Coulomb exchange effects coupling the generated excitons and that the oscillation frequency and amplitude depend nonlinearly on the Rabi frequency of the incident field.

Chromium is deposited epitaxially onto Au(100), Ag(100), and Cu(100), and the effect of the substrate lattice constant on the Cr 3d states is determined with inverse photoemission. A 1×1, 1×1, and 3×1 registry is found, respectively. For a monolayer of Cr on Au(100) and Ag(100) we find peaks at 1.8 and 1.6 eV above the Fermi level, respectively, which is assigned to a ${\mathrm{\Delta }}_5$(${\mathit{d}}_{\mathit{x}\mathit{z},}$yz) state. Together with photoemission results this implies a magnetic splitting of 2.5–2.6 eV and 2.7 eV, respectively, which is consistent with theoretical predictions of enhanced monolayer magnetism. For a Cr monolayer on Cu(100) we observe a peak at 1.0 eV that lies between the two magnetically split states on Au(100) and Ag(100). This is consistent with a collapse of the magnetic splitting caused by the lateral compression of the Cr film on Cu(100) relative to Ag(100) and Au(100).

In the recent experimental paper on ultrathin Pd overlayers on Pt(111), Han, Mrozek, and Wieckowski [Phys. Rev. B 48, 8329 (1993)] present the coverage dependence of Pd core-level shifts (CLS’s). They conclude that the results obtained can be explained as originating from initial-state effects and they give a broad discussion of CLS’s in related systems. We attempt to show here that the initial-state picture is consistent with most of the effects mentioned. Particularly, we employ a self-consistent tight-binding model to calculate the chemical shifts for the epitaxial Pd overlayer and small Pd clusters on Pt(111). The calculated values (-0.2 eV for overlayer and -0.6 eV for cluster atoms) are in reasonable agreement with the experiment and corroborate the initial-state interpretation. This does not mean inevitably, however, that the final-state picture can be ruled out.

Using a simple model, it is demonstrated that l=3 partial waves contribute significantly to the description of the exponentially decaying charge distribution at metal surfaces calculated within the atomic-sphere approximation. Despite a partially compensating error in the calculated Fermi level, truncating at l=2 overestimates calculated work functions by up to 0.7 eV or 15%, while trends are well established. The better converged results improve agreement with experiment for the late-row metals, but generally result in poorer agreement for the bcc transition metals.

Measurements down to 0.06 K indicate that the Hall coefficient of Si:P diverges as the metal-insulator transition is approached, in contrast with an earlier report by Koon and Castner for Si:As, and in disagreement with their claim for Si:P. We show that zero-temperature extrapolations deduced from data above 0.5 K, the range used in the earlier experiments, can yield a Hall coefficient that appears to remain finite.

A phenomenological Ginzburg-Landau theory is applied to the normal phase of one-dimensional charge-density-wave systems with a finite concentration of impurities. It is found that the interaction between the impurities and the highly polarizable electron gas leads to a strong and oscillatory impurity-impurity interaction, which in turn leads to ordered impurity arrangements and to sizable periodic lattice distortions. The effect is very strongly dependent on the charge of the impurities, their concentration, and their (interstitial) location in the lattice unit cell. All these factors modify drastically the periodicity associated with the lattice distortion. The theory explains satisfactorily the changing modulation recently observed by atomic-force microscopy in the normal (room-temperature) phase of ${\mathrm{NbSe}}_3$ with a variety of impurities.

We study the properties of a quarter-filled system of electrons on a square lattice interacting through a local repulsion U and a nearest-neighbor repulsion V in the limit V=+∞. We identify the ground state for U large enough and show that domain walls appear below a critical value ${\mathit{U}}_{\mathit{c}}$=4t/π. We argue that this corresponds to a metal-insulator transition due to Mott localization.

The results of electronic-structure calculations for ${\mathrm{GeCuO}}_3$ feature a pair of narrow (∼1 eV) half-filled, one-dimensional ${\mathrm{\sigma }}^{\mathrm{*}}$ conduction bands that originate from two edge-sharing ${\mathrm{CuO}}_2$ linear chains in the orthorhombic cell. Unusual transport properties are predicted since the confined carrier motion along the chains (at any band filling) requires tunneling through nodal charge-density regions. At the spin-Peierls transition, the dimerization of the ${\mathrm{CuO}}_2$ chains can open a band gap at ${\mathit{E}}_{\mathit{F}}$, provided that the Cu displacements in neighboring chains are staggered.

We report photoluminescence measurements on low-disorder, dilute (p≃6×${10}^{10}$ ${\mathrm{cm}}^{\mathrm{-}1}$), two-dimensional (2D) hole systems in GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As quantum wells at low Landau-level filling factors (ν). Near and below ν=1/3 we observe two additional lines in the spectra. One of these, appearing ≊0.8 meV below the main line, is similar to a line observed in 2D electron systems at very low ν (≲1/5), which has been attributed to the condensation of 2D electrons into a Wigner solid. The other, observed ≊4 meV below the main line, has no apparent counterpart in 2D electron systems. We interpret the data as consistent with the magnetic-field-induced localization of 2D holes, possibly into a pinned Wigner solid state.

We study the critical field for the formation of Wannier-Stark ladders and Bloch oscillations in $\frac{\mathrm{GaAs}}{{\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}}$ superlattices at low temperatures. From the results of photocurrent and transient four-wave mixing experiments, we conclude that the critical field is higher for superlattices with wide minibands than for superlattices, with narrow minibands. The explanation for this dependence is that intraminiband scattering due to LO-phonon emission is excluded in minibands narrower than the LO-phonon energy.