Conductivity of a coupled two-channel dirty Tomonaga-Luttinger model is calculated from the Mori formalism. We find that the conductivity becomes enhanced as the interchannel interaction is turned on even when the interaction is repulsive. This effect is opposite to those from the 2${\mathit{K}}_{\mathit{F}}$ charge-fluctuation coupling in systems with the channel separation <1/${\mathit{k}}_{\mathit{F}}$, and is considered to come from the suppressed charge-density-wave fluctuations.

A form of the exchange potential for the jellium metal surface is derived through functional differentiation of the exchange-energy functional by considering variations restricted to a particular class of densities. The potential satisfies the virial-theorem sum rule, possesses the correct scaling property, and satisfies the second-derivative condition. It is the sum of two parts: the first being explicitly written in terms of the Slater potential created by the Fermi hole, the electronic density, and their gradients. This contribution is shown to contain already the exact asymptotic properties of the full exchange potential, viz., the image potential structure in the vacuum and the Gasper-Kohn-Sham value in the metal bulk. As a consequence of the restricted variations, the second contribution is not explicitly known. Nevertheless, it is short ranged, satisfies itself an important sum rule, and has the required scaling property. For slowly varying densities, it depends upon terms of O(∇ρ,${\mathrm{\nabla }}^2$ρ). The known component itself also satisfies the virial theorem and the scaling condition. Furthermore, within an approximation for the functional derivative of the Slater potential, this component satisfies the second functional derivative condition as well as the sum rule relating the exchange potential to its functional derivative.

We discuss a generalization of the conventional bosonization procedure to the case of current-current interactions which have a natural representation in terms of current instead of fermion-number-density operators. A consistent bosonization procedure requires a geometrical quantization of the Hamiltonian action of ${\mathit{W}}_{\mathrm{\infty }}$ on its coadjoint orbits. An integrable example of a nontrivial realization of this symmetry is presented by the Calogero-Sutherland model. For an illustrative nonintegrable example we consider transverse gauge interactions and calculate the fermion Green function.

Using scanning tunneling microscopy (STM), we studied 1T-${\mathrm{TaS}}_2$ in all four of its charge-density-wave (CDW) supporting phases over the temperature range 360–143 K. Special attention was given to the search for discommensurate structures and the distinguishing of true CDW discommensurations and domains from apparent discommensurations and domains formed by interference between the CDW and the atomic lattice. In the lowest-temperature commensurate (C) phase, we find that the CDW is in the commensurate configuration as expected. We use the C phase to investigate the effects of multiple tips and find that shifts in the apparent registration of the CDW relative to the atomic lattice result. In the nearly commensurate (NC) phase, the CDW is in a true domain structure as evidenced by satellite spots in the Fourier transforms of the STM images. In the triclinic (T) phase, the STM data indicate that the CDW is in a striped domain phase, which is significantly different from the domain model previously proposed. Finally, in the high-temperature incommensurate (I) phase, we find unexpected satellite spots in the STM Fourier transforms, suggesting that a CDW modulation is also present in this phase.

The ${}_{}{}^5{}_{}{}^{}$${\mathit{D}}_{0\mathrm{-}}^7$${\mathit{F}}_0$ transition mechanism has been investigated for the ${\mathrm{Eu}}^{3+}$ ion in two kinds of oxide glasses, polyvinyl alcohol film, and ${\mathrm{Y}}_2$${\mathrm{O}}_2$S crystal powder, from the analysis of the laser-induced fluorescence spectra. In the case of ${\mathrm{Eu}}^{3+}$ in sodium silicate glass and sodium germanate glass, it has been found that the ${}_{}{}^5{}_{}{}^{}$${\mathit{D}}_{0\mathrm{-}}^7$${\mathit{F}}_0$ transition probability of the ions site-selected by the laser-light excitation is approximately proportional to the square of the axial second-order crystal-field parameter ${\mathit{B}}_{20}$. The interpretation of this result is that the dominant mechanism of this transition in these two glasses is due to the borrowing of intensity from the ${}_{}{}^5{}_{}{}^{}$${\mathit{D}}_{0\mathrm{-}}^7$${\mathit{F}}_2$ (${\mathit{M}}_{\mathit{J}}$=0) transition by the J-mixing effect. In the case of polyvinyl alcohol:${\mathrm{Eu}}^{3+}$ and ${\mathrm{Y}}_2$${\mathrm{O}}_2$S:${\mathrm{Eu}}^{3+}$, on the other hand, the contribution of this mechanism has been found to be negligible, from the analysis of the intensity ratio between the ${}_{}{}^5{}_{}{}^{}$${\mathit{D}}_{0\mathrm{-}}^7$${\mathit{F}}_0$ and ${}_{}{}^5{}_{}{}^{}$${\mathit{D}}_{0\mathrm{-}}^7$${\mathit{F}}_2$ transitions. Furthermore, in the above two kinds of glass samples, the site-to-site variations in the energy of the ${}_{}{}^7{}_{}{}^{}$${\mathit{F}}_0$ state and the mean energy of the three ${}_{}{}^7{}_{}{}^{}$${\mathit{F}}_1$ Stark levels are explained well by the mixing of the ${}_{}{}^7{}_{}{}^{}$${\mathit{F}}_2$ state due to the second-order crystal-field potential. To explain the above energy variations in polyvinyl alcohol:${\mathrm{Eu}}^{3+}$, however, it is necessary, in addition to this effect, to take into account the mixing of the charge-transfer state and/or the J mixing due to the other components of the crystal-field potential.

The electronic and vibrational properties of a gold-related center in silicon have been studied by Fourier-transform spectroscopy using uniaxial stress and Zeeman spectroscopy. Thirteen different characteristic line series have been identified, of which 11 consist of a relatively intense zero-phonon line followed by several phonon replicas. The line series are assigned to internal transitions at a gold-related center in two different charge states, i.e., the neutral and negatively charged states for which the phonon energy is about 119.8 and 105.7 ${\mathrm{cm}}^{\mathrm{-}1}$, respectively. A Huang-Rhys factor of 1.4±0.1 was determined for the ħω=119.8 ${\mathrm{cm}}^{\mathrm{-}1}$ series. The center has trigonal symmetry deduced from uniaxial stress and Zeeman experiments. A dissociation energy of about 1.7 eV was determined from an isothermal annealing study. The trigonal symmetry and the high dissociation energy strongly suggest that the center consists of two nearest-neighbor substitutional gold atoms. A divacancy model is employed that makes a qualitative understanding of the electronic properties of the center possible.

Rigorous dipole selection rules are derived for an interacting electron-hole system in a multiband semiconductor. The electronic system is described by the Coulomb many-body Hamiltonian and the valence-band structure is modeled using the Luttinger Hamiltonian in the axial approximation. For the example of a third-order analysis of polarization dependent two- and three-beam four-wave-mixing experiments the polarizations of the mixing signals are computed. Besides situations with well-defined four-wave-mixing polarizations configurations are identified where the polarization state of the outgoing signal depends on the dynamic and coherent properties of the semiconductor.

Molecular-dynamics calculations of simple defect production in bulk Si are reported. The Tersoff three-body potential-energy function is used to provide a realistic lattice-atom interaction potential. The displacement-threshold energy ${\mathit{E}}_{\mathit{d}}$ is calculated as a function of the initial primary knock-on momentum direction, and the formation energies for resulting defect structures are obtained. In addition, we determine the effect of the vacancy-interstitial separation on the anisotropy in ${\mathit{E}}_{\mathit{d}}$, where the criterion for stable Frenkel-pair defect formation is assumed to require a certain minimum separation. The resultant angular dependent ${\mathit{E}}_{\mathit{d}}$ versus (θ,φ) is compared with that proposed by Hemment and Stevens (HS) to account for the magnitude and anisotropy of the observed energetic electron-induced radiation damage in Si. The anisotropy of our ${\mathit{E}}_{\mathit{d}}$ surface is consistent with that of HS provided a lower limit of 4 Å is placed on the initial Frenkel-pair separation for the production of long-lived damage. The relatively large formation energy of 8.4 eV which we obtain for such widely separated vacancy-interstitial pairs indicates that the individual point defects are essentially isolated (i.e., noninteracting). More closely spaced vacancy-interstitial complexes are also identified, which have lower formation energies. While it is argued that these complexes are relatively short lived, they may be relevant to dynamical processes such as beam-enhanced molecular-beam epitaxy, atomic mixing at interfaces, and ‘‘subthreshold’’ damage production.

We have observed cyclotron resonance and impurity cyclotron resonance (1s-2${\mathit{p}}^{+}$ transition) in a wide far-infrared wavelength range between 9.27 and 70.5 μm under pulsed high magnetic fields up to 180 T. A very large resonant polaron effect reflecting a large electron-phonon coupling constant was observed in both resonances, as well as a large nonparabolicity. The experimental results of cyclotron resonance were found to be in good agreement with a theoretical calculation based on the Wigner-Brillouin second-order perturbation theory taking account of the nonparabolicity. The impurity cyclotron-resonance data can also be well explained by a variational calculation. The donor ionization energy was found to increase by a factor of 2.39 at 180 T due to the magnetic freeze-out effect.

The paper deals with optical second-harmonic generation in a medium absorbing the second-harmonic radiation, and where phase matching between the fundamental and second-harmonic radiation is not necessarily achieved. We first take the waves to be in the form of traveling waves, and describe the damping of the fundamental beam due to harmonic creation. It is found that both second-harmonic absorption and phase mismatch enhance the depletion length of the pump wave. Before depletion, the second-harmonic output power is independent of the traversed thickness if it exceeds the second-harmonic attenuation length. When depletion occurs, the second-harmonic output power is constant, instead of quadratic, in the input power. Next, second-harmonic generation in a plane-parallel plate of lossy material is envisaged in the case of normal incidence, including the multiple reflections expected in high-reflectance materials. The expressions of the harmonic output intensity, transmitted or reflected, of this paper and from the conventional treatment, are compared. The deviation is noticeable in the case of the transmitted harmonic power, and may be considerable in the case of the reflected power. Last, measurements of the second-harmonic output intensity in GaSe and InSe are reported at a fundamental wavelength of 1.06 μm. The sample dependence is in good agreement with our theory, which in turn is applied to derive new values of the nonlinear optical susceptibilities in the layered-structured III-VI materials. The treatment is fully analytical and may be applied to a wealth of materials.

Structurally metastable iron-boron pairs in silicon have been detected using dark- or photocapacitance transient techniques combined with minority-carrier injection below 200 K. Five levels at ${\mathit{E}}_{\mathit{C}}$-0.43, 0.46, 0.52, and 0.54 eV and ${\mathit{E}}_{\mathit{V}}$+0.53 eV are observed as the metastable defects after the injection. The creation and annihilation behaviors of these defects by the injection are investigated in detail and discussed on the basis of the theory of recombination-enhanced defect reaction. The transmutations for respective defects are confirmed by isochronal anneals and the reaction kinetics are studied by isothermal anneals. These kinetic studies lead to a model for pair configurations responsible for these defect levels. The configuration-coordinate (CC) description for these metastable pairs is shown to account for all electrical and thermal properties. The CC model shows us why the metastability for the iron-boron pair cannot be observed in thermal equilibrium.

The electrical behavior of the ${\mathrm{TlInTe}}_2$ ternary semiconductor is studied in the negative-differential-resistance region of its S-type I-V characteristic. Self-excited voltage oscillations in this region, with an amplitude of about 5 V were monitored at temperatures above 70 K. An analysis of the dynamic behavior of these oscillations by means of the Grassberger and Proccacia method shows the existence of two components in the signal, a quasiperiodic component and a chaotic component. Furthermore, this analysis leads to the estimation of fractal dimensions, minimum embedding dimensions and Kolmogorov entropies that characterize the two components.

The electron-paramagnetic-resonance transitions of isolated neutral interstitial iron (${\mathrm{Fe}}_{\mathit{i}}^0$) in n-type silicon show a satellite structure, which is clearly detectable for donor concentrations (P or As, respectively) above ${10}^{15}$ ${\mathrm{cm}}^{\mathrm{-}3}$. The satellite structure reflects the hyperfine interaction with one shallow-donor nucleus and one iron nucleus in the case of doping with ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$. The spectra are explained by the spin-spin interaction of one ${\mathrm{Fe}}_{\mathit{i}}^0$ (spin ${\mathit{S}}_{\mathrm{Fe}}$=1) and one shallow donor (spin ${\mathit{S}}_{\mathit{D}}$=1/2). Neither line positions nor line shapes depend on the direction of the magnetic field with respect to the crystal axes. A random distribution of distant iron-donor pairs is suggested by the following facts. Both (${\mathit{S}}_{\mathrm{Fe}}$+${\mathit{S}}_{\mathit{D}}$) levels (high-field satellites) and (${\mathit{S}}_{\mathrm{Fe}}$-${\mathit{S}}_{\mathit{D}}$) levels (low-field satellites) are thermally populated. Asymmetric line shapes and dissimilar hyperfine components indicate a continuous distribution of spin-spin interaction parameters.

Relaxation of holes photoexcited to the splitoff valence band by femtosecond pulses in the mid-infrared is directly monitored via the transient inter-valence-band absorption. Two thermalization processes are distinguished. The excited carriers undergo inter-valence-band scattering within 100 fs and thermalize with time constants around 700 fs. In contrast, equilibration of unexcited holes occurs within 100 fs. Theoretical calculations show that the dynamically screened Coulomb interaction among the holes and emission of optical phonons represent the main scattering mechanisms.

In ZnSe crystals grown by different techniques, titanium ions are incorporated as ${\mathrm{Ti}}^{2+}$(${\mathit{d}}^2$) and ${\mathrm{Ti}}^{3+}$(${\mathit{d}}^1$) centers on Zn sites. A strong Jahn-Teller (JT) effect acts on the doubly degenerate ${}_{}{}^2{}_{}{}^{}$E ground state of ${\mathrm{Ti}}^{3+}$. The electron paramagnetic resonance (EPR) at T=3 K indicates a quasistatic JT effect of the ground state and a quasidynamic one of the first excited state for the strain-split vibronic ${}_{}{}^2{}_{}{}^{}$E${\mathrm{-}}^2$${\mathit{A}}_2$ manifold. These effects are distinguished by their angular variations and the g values. ${\mathrm{Ti}}^{2+}$ causes an isotropic EPR signal. Excitation and sensitization spectra of ${\mathrm{Ti}}^{2+}$ and ${\mathrm{Ti}}^{3+}$ luminescence transitions are explained within a one-electron model connecting internal (d-d) with charge-transfer transitions involving the valence and conduction bands. Both charge states are sensitive to illumination with near-infrared light. The ions can be mutually converted, as shown by photo-EPR and sensitization experiments. The ${\mathrm{Ti}}^{2+}$/${\mathrm{Ti}}^{3+}$ donor level is situated approximately 8500 ${\mathrm{cm}}^{\mathrm{-}1}$ below the edge of the conduction band.

A Fermi-surface study of palladium disilicide is presented. Experimentally, the Fermi surface and the cyclotron effective masses have been studied using the de Haas–van Alphen (dHvA) effect. Theoretically, the band structure of ${\mathrm{Pd}}_2$Si has been calculated using the linear-muffin-tin-orbital method in the atomic-sphere approximation. The Fermi surface consists of three small hole pockets, an open hole surface, and two large electron sheets. The calculated angular dependence of the extremal cross sections of the Fermi surface is in reasonable agreement with dHvA experiments. Some additional dHvA oscillations are predicted.

Far-infrared magnetotransmission of strained epitaxially grown n-type PbTe was investigated using experiments in the Faraday (B∥[111]) and Voigt (B∥[11¯0]) configurations. The analysis of the data is based on a complete frequency-dependent dielectric function for both magnetic-field configurations, taking into account explicitly the effects of the strain splitting of the four L states in the Brillouin zone. The experiments were performed at temperatures ranging from 1.4 K to 20 K and the dependence of the Fermi energy on magnetic field, temperature, as well as the strain splitting were calculated within the Mitchell-Wllis k⋅p scheme. It is shown that this method is capable of determining strain-induced shifts of equivalent L states with an accuracy of about 0.5 meV. These techniques are applicable to other strained many-valley systems such as Si/SiGe.

The neutral vacancy (V) and the {V,${\mathrm{H}}_{\mathit{n}}$} (n=1,...,4) complexes in silicon are studied in various molecular clusters at the approximate ab initio and ab initio Hartree-Fock levels, with post-Hartree-Fock corrections in electron correlation. The quantities calculated are the equilibrium configurations and electronic structures, dissociation energies, diffusion paths, and activation energies. The dissociation energies are compared to those of other traps for H calculated at the same level of theory, such as substitutional C, interstitial Ti, or the {B,H} pair. The calculations predict that the {V,${\mathrm{H}}_1$} pair in Si should be mobile above room temperature. A part of the barrier for diffusion of {V,${\mathrm{H}}_1$} is lower than that of V, due to a mechanism analogous to the H-enhanced diffusion of interstitial O in Si. Another part of this barrier is higher than that for V. The consequences of this process include the possibility of enhanced diffusion of H in polycrystalline versus crystalline Si and leads us to propose a mechanism for the nucleation of platelets in the subsurface region of plasma-exposed Si.

We have studied picosecond two-pulse degenerate four-wave mixing in GaAs/AlAs quantum wells under different polarization configurations of the two pump beams and the analyzed optical polarization. We observe two components, a prompt free polarization decay (FPD) and a delayed photon echo (PE), which show different polarization rules and dephasing times. The observed polarization rules are consistently explained in a theoretical model. Within this model, the two-component behavior is a direct consequence of short-range disorder. The PE dephasing rate is associated with the homogeneous broadening of the excitons while the FPD corresponds to the total dephasing rate, consisting of the homogeneous and inhomogeneous (short-range and long-range) broadenings.