The effect of the Coulomb charging energy on the time evolution of the electron wave packet in a coupled-quantum-dot structure is investigated by use of coupled equations derived from the Schrödinger equation. As long as the Coulomb charging energy does not exceed a certain threshold energy (four times as much as the coupling energy between the dots), the electron wave packet, which was initially localized in one of the dots, is completely transferred to the other dot and oscillates back and forth between the two dots. If the Coulomb charging energy exceeds the threshold, the transfer rate of the wave packet becomes abruptly incomplete and is reduced to less than one-half. This effect may be called the Coulomb blockade of the resonant electron tunneling in coupled quantum dots. It should be stressed that the transfer period of the wave packet is remarkably increased at and near the threshold charging energy. The analysis presented here should provide a useful basis for the design and evaluation of mesoscopic devices operating with coupled quantum structures.

The 7×7 surface has been studied with Si 2p core-level spectroscopy using an experimental resolution better than 70 meV at a temperature of 120 K. The spectra are much more well resolved than earlier reports and provide considerably more information. They consist of a bulk component and five surface components, three of which appear as peaks or shoulders in the spectra. We find that the component that is shifted 0.70 eV to lower binding energies (${\mathit{S}}_2$) is due to the rest atoms. The contribution from the adatoms is revealed by a component, twice as large as ${\mathit{S}}_2$, shifted 0.53 eV to higher binding energies.

We study how fractal roughness on inert electrode surface affects the ac impedance of electrochemical cells. Using Koch curves to represent the electrode surface in two dimensions, we analyze the diffusion and migration of ions in an ac field from first principles. We find that, although fractal roughness leads to a constant-phase-angle (CPA) impedance, it is both outside the experimental frequency range and masked by the bulk relaxation of the electrolyte. This result rules out previous attempts to explain the CPA impedance in terms of transport processes. We suggest that ion adsorption and/or desorption on the surface is the most likely explanation.

Time-resolved (TR) four-wave mixing (FWM) experiments are performed on a high-quality GaAs quantum-well sample where biexcitons make the dominant contribution under certain experimental conditions. TR-FWM peaks well after both beams passed through, regardless of relative contributions of biexcitons to FWM. Our experiments show that the diffraction of the interaction-induced field dominates FWM from biexcitons, as well as from excitons.

The frequency-domain four-wave-mixing response of excitons in GaAs in a magnetic field is theoretically and experimentally studied. For linearly cross-polarized excitation beams, the application of a magnetic field induces a resonance that leads to the observation of a narrow dip in the primary resonance. The primary resonance has a width given by the exciton spin-flip rate while the narrow dip has a width determined by the recombination rate. The results reflect the dynamics of two observables defined in terms of the appropriate Fourier components of the net population and the net population transfer between the two oppositely spin-oriented excitonic states, similar to the normal decay modes of the system. The relative amplitude of these observables is determined by the relative polarization of the incident fields and the strength of the applied magnetic field.

Femtosecond photoexcitation near, but above, the band gap in GaAs epitaxial layers and doped heterostructures in magnetic fields is shown to produce transient coherent cyclotron emission, lasting for several picoseconds at low temperatures. This emission reflects the relatively long phase relaxation of coherent electronic excitations associated with free electron inter-Landau-level transitions. In a doped, wide parabolic quantum well, the photoexcited carriers drive the magnetoplasmon mode of the equilibrium carriers, producing a dramatic resonance as the cyclotron frequency crosses the magnetoplasmon frequency.

Gain and absorption spectra in ZnSe-based blue-green diode lasers have been measured to show the role of pairwise Coulomb correlation between electrons and holes in ${\mathrm{Zn}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Cd}}_{\mathit{x}}$Se/${\mathrm{Zn}}_{1\mathrm{-}\mathit{x}}$${\mathrm{S}}_{\mathit{x}}$Se quantum wells (QW’s) under lasing conditions at room temperature. In addition, the radiative decay rates of electron-hole pairs have been obtained from time-resolved photoluminescence measurements over a wide temperature range. These experiments also point out the importance of the Coulomb interactions on the QW optical properties near its fundamental absorption edge under device operating conditions.

We investigate the intersubband relaxation in GaAs quantum wells at room temperature using differential transmission spectroscopy with subpicosecond time resolution. The dynamics of the subband populations are derived from the experimentally observed reduction of oscillator strength of the corresponding exciton transitions. The obtained electron intersubband scattering times are 160 fs for relaxation from the second to the first subband in a 15-nm quantum well and 170 fs for relaxation from the third to the first subband in a 20-nm structure. These times are significantly shorter than those deduced from previous experiments and from some theoretical studies.

We present measurements of the magnetic field dependence of the insulator transition in a gated ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs heterostructure. The resulting phase diagram shows reentrant behavior as the magnetic length decreases below the zero-field electron mean free path. By fitting our data to a predicted phase diagram, we obtain a value for the localization length exponent governing the quantum-Hall-liquid–insulator transition. As has been recently suggested, this value is in agreement with that determined for the critical exponent between quantum Hall plateaus.

Using a finite-frequency recursive Green’s-function technique, we calculate the dynamic magnetoconductance fluctuations and oscillations in disordered mesoscopic normal-metal systems, incorporating interparticle Coulomb interactions within a self-consistent potential method. In a disorderd metal wire, we observe ergodic behavior in the dynamic conductance fluctuations. At low ω, the real part of the conductance fluctuations is essentially given by the dc universal conductance fluctuations while the imaginary part increases linearly from zero, but for ω greater than the Thouless energy and temperature, the fluctuations decrease as ${\mathrm{\omega }}^{\mathrm{-}1/2}$. Similar frequency-dependent behavior is found for the Aharonov-Bohm oscillations in a metal ring. However, the Al’tshuler-Aronov-Spivak oscillations, which predominate at high temperatures or in rings with many channels, are strongly suppressed at high frequencies, leading to interesting crossover effects in the ω dependence of the magnetoconductance oscillations.

A negative electron affinity (NEA) was found both experimentally by photoemission spectroscopy and theoretically by ab initio calculations for the 2×1 reconstructed diamond (100) surface. This surface is the dominant growth surface for thin diamond films and can be obtained by chemical-vapor deposition. Various surface-preparation methods which result in a NEA are described. Theoretical results indicate that the observed NEA is associated with a monohydride-terminated surface, while the hydrogen-free surface exhibits a positive electron affinity.

Nearly coherent overlayers of ${\mathrm{CoSi}}_2$ were grown on Si(111) by molecular-beam epitaxy and examined by an in situ scanning-tunneling microscope at 77 K. The quantum-size effect in ${\mathrm{CoSi}}_2$ overlayers was demonstrated using scanning-tunneling microscopy. Subbands in the ${\mathrm{\Lambda }}_1$ and ${\mathrm{\Lambda }}_3$ energy bands along the ΓL symmetry line were observed, and the observed subband spacings agree well with independent band-structure computations.

Using a scanning tunneling microscope, the growth of ${\mathrm{C}}_{60}$ on Ag(110) is explored. The substrate influences the natural tendency of the fullerene molecules to pack closely and an overlayer system with twofold rotational symmetry is formed: Ag(110)c(4×4)${\mathrm{C}}_{60}$. This represents a distorted close-packed configuration for the ${\mathrm{C}}_{60}$ molecules, where the nearest-neighbor distance observed in bulk ${\mathrm{C}}_{60}$ is maintained. Initial island growth occurs on terrace sites away from substrate step edges, which bunch with increasing fullerene coverage. Above monolayer coverage, ${\mathrm{C}}_{60}$ grows epitaxially, maintaining twofold rotational symmetry. Tunneling spectroscopy is used to explore differences between the electronic structure in the monolayer and multilayer regimes.

Ultrahigh-pressure transformations in the ${\mathrm{Ce}}_{0.43}$${\mathrm{Th}}_{0.57}$ alloy were investigated up to 253 GPa (volume compression V/${\mathit{V}}_0$=0.402) in a diamond anvil cell utilizing synchrotron x-ray diffraction. Unlike Ce, a first-order isostructural–fcc-to-fcc transition under pressure was not observed in this alloy. At the initiation of f-electron bonding, the fcc-to-bct transition was observed at 17 GPa. This pressure is close to the corresponding transition pressure in Ce metal (12 GPa) and is considerably lower than that in Th metal (60 GPa). The present experiments suggest that there are strong nonlinearities in transition pressure as a function of alloying content for f-electron alloys.

An optical study of ${\mathrm{LiKSO}}_4$ crystals under uniaxial pressure is presented. The evolution of the birefringence Δ${\mathit{n}}_{\mathit{a}\mathit{b}}$ and Δ${\mathit{n}}_{\mathit{b}\mathit{c}}$ has been measured in the temperature range 100–300 K. A ferroelastic monodomain has been induced in the biaxial low-temperature phase by means of uniaxial pressure applied perpendicular to the c axis. The dependence of the birefringence Δ${\mathit{n}}_{\mathit{a}\mathit{b}}$ with respect to the applied uniaxial pressure ${\mathrm{\sigma }}_{\mathit{y}\mathit{y}}$ has been measured and related to the piezo-optic coefficients ${\mathrm{\pi }}_{\mathit{i}\mathit{j}}$. Our conclusions seem to conciliate the discrepancies presented in previous optical studies of ${\mathrm{LiKSO}}_4$ crystals.

This work reports the excitation and luminescence spectra at T=9 K of the ${\mathrm{Mn}}^{2+}$-doped ${\mathrm{RbCdF}}_3$, ${\mathrm{RbCaF}}_3$, and ${\mathrm{CsCaF}}_3$ fluoroperovskites. A ${\mathrm{Mn}}^{2+}$ concentration down to 400 ppm has been detected. The present data together with those available for ${\mathrm{KMgF}}_3$:${\mathrm{Mn}}^{2+}$, ${\mathrm{KZnF}}_3$:${\mathrm{Mn}}^{2+}$, ${\mathrm{KMnF}}_3$, and ${\mathrm{RbMnF}}_3$, allow us to explore the variations of the zero-phonon line (ZPL) and the Stokes shift [associated with the ${\mathrm{Mn}}^{2+}$ luminescent ${}_{}{}^4{}_{}{}^{}$${\mathit{T}}_{1\mathit{g}}$(G)${\to }^6$${\mathit{A}}_{1\mathit{g}}$(S) transition] along the whole series of cubic fluoroperovskites doped with ${\mathrm{Mn}}^{2+}$ in order to investigate their dependence with the Mn-F distance, R. The experimental variation of the ZPL energy measured in the 206–215 pm range is ${\mathit{E}}_{\mathrm{ZPL}}$=-21 305+187R (pm). This strong dependence of ZPL upon R allows one to measure Mn-F distances along the series of fluoroperovskites with accuracies of better than 0.001 Å, thus improving by more than one order of magnitude the extended x-ray-absorption fine structure resolution. Furthermore, this sensitivity is extended down to ${10}^{\mathrm{-}4}$ Å when we analyze the variations δR induced by pressure in a given system. As regards Δ${\mathit{E}}_{\mathit{s}}$, the present results on ${\mathrm{Mn}}^{2+}$-doped fluoroperovskites demonstrate an increase of the Stokes shift when R increases. This behavior is explained to be related to a Grüneisen constant γ(${\mathit{a}}_{1\mathit{g}}$) corresponding to the symmetric mode of the complex. The value of the constant is greater than 1.9, in agreement with calculations on divalent transition-metal complexes like ${\mathrm{MnF}}_6^{4\mathrm{-}}$ and ${\mathrm{VF}}_6^{4\mathrm{-}}$. The importance of the present results for the observation of luminescence through the full series of ${\mathrm{Mn}}^{2+}$-doped fluoroperovskites is also discussed.

By using the high-accuracy universal polarimeter, all the components of optical activity tensor g and birefringence Δn of ${\mathrm{Rb}}_2$${\mathrm{ZnCl}}_4$, which were studied in limited part before, have been reexamined. A unique component, ${\mathit{g}}_{23}$, was definitely found to appear both in the incommensurate and ferroelectric phases, but all the other components vanished in the two phases. The previous report is revised. It manifests a similar temperature dependence to that found in [N(${\mathrm{CH}}_3$${)}_4$${]}_2$${\mathrm{ZnCl}}_4$; it changes the sign within the temperature region of the incommensurate phase. This phenomenon can be interpreted as due to the difference of optical gyration of soliton regions and that of the commensurate domains. It was confirmed that the critical exponent, approximately 0.42, of the temperature dependence of ${\mathit{g}}_{23}$ agrees with nearly constant values shown by other various ${\mathit{A}}_2$${\mathit{BX}}_4$ crystals. However, temperature, where the multisoliton region emerges, was found to differ considerably from that of [N(${\mathrm{CH}}_3$${)}_4$${]}_2$${\mathrm{ZnCl}}_4$.

The energy of vacancy formation ${\mathit{E}}_{\mathit{v}}$ is discussed in the framework of a cluster model. It is shown that this value depends on the vacancies concentration in a metal, ${\mathit{c}}_{\mathit{v}}$, and has a form ${\mathit{E}}_{\mathit{v}}$=${\mathit{E}}_{\mathit{v},\mathrm{c}\mathrm{r}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{l}}$(0) -1/3${\mathit{Ac}}_{\mathit{v}}^{1/3}$ where the second term takes into consideration the surface of the clusters and the first term is concentration independent [${\mathit{E}}_{\mathit{v},\mathrm{c}\mathrm{r}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{l}}$(0) and A are constants]. The additional term makes it possible to explain the curvature of self-diffusion plots in metals. Numerical results are obtained for Cu and β-Ti in the tight-binding model.