Showing papers on "Effective mass (solid-state physics) published in 1988"
TL;DR: The CuO/sub 2/ planes in the high-temperature superconductors are described by a two-dimensional Hubbard model and a pair of holes, which naively should be quite mobile, are found to be extremely heavy due to a previously unappreciated frustration effect that impedes their motion.
Abstract: The ${\mathrm{CuO}}_{2}$ planes in the high-temperature superconductors are described by a two-dimensional Hubbard model. The model is investigated for an infinite system with one and two electrons less than half filling. The method used is to diagonalize the Hamiltonian exactly within a retained portion of the Hilbert space. A single hole is found not to be localized by a string potential that increases linearly with distance, although it does have a large effective mass. A pair of holes, which naively should be quite mobile, is found instead to be extremely heavy due to a previously unappreciated frustration effect that impedes their motion. This lack of mobility increases the energy of the pair so that they do not bind, contrary to some recently published results using mean field theory or intuitive arguments. The energy of one- and two-hole states is calculated as a function of wavevector k. The comparative energy of different angular momentum channels and magnetic polaron effects are discussed.
259 citations
TL;DR: A spin-orbital splitting of the 2D spectrum of electrons and also of heavy and light holes in the GaAs quantum well caused by k 3 -terms in the bulk dispersion law is calculated in this paper.
122 citations
TL;DR: In this article, the authors describe fabrication and photoluminescence excitation of InGaAs/InP quantum wires with a lateral dimension of ∼350 A. The exciton energies agree with the theoretical predictions based on a new method of solving the two-dimensional effective mass Schrodinger equation.
Abstract: We describe fabrication and photoluminescence excitation of InGaAs/InP quantum wires with a lateral dimension of ∼350 A. Transverse confinement results in the splitting of the n=1 heavy hole‐electron transition. Three of these levels are observed in the excitation spectrum. The exciton energies agree with the theoretical predictions based on a new method of solving the two‐dimensional effective mass Schrodinger equation.
116 citations
TL;DR: In this article, the temperature dependence of the intrinsic carrier concentration n i in InSb is determined between 200 K and the melting point of the compound (798 K), and an empirical formula describing the temperature variation of n i is proposed.
114 citations
TL;DR: In this paper, the authors analyzed the excitonic properties in quantum-wire structures (QWS) by taking into account the band-mixing effects in the valence band of the structure and found that the effective mass value in the wire direction at the zone center of the lowest heavy-hole-like subband is as small as 0.027 m/sub 0/ for GaAs/AlGaAs QWS.
Abstract: The excitonic properties in quantum-wire structures (QWS) are analyzed by taking into account the band-mixing effects in the valence band of the structure. The effective mass value in the wire direction at the zone center of the lowest heavy-hole-like subband is found to be as small as 0.027 m/sub 0/ for GaAs/AlGaAs QWS. This reduced effective mass and the related nonparabolicity of the subband structure play a significant role in determining the exciton properties. Using these results, the maximum excitonic contribution to the refractive index value is estimated to be 0.59, i.e. 17.4% of the bulk value for a GaAs/Al/sub 0.4/Ga/sub 0.6/As QWS with a 50 A*50 AA cross section. This value is six times larger than that in the 50-AA quantum well. With an electric field of 8*10/sup 4/ V/cm perpendicular to the heterointerface, a maximum refractive index change 30% larger than this value is estimated. >
105 citations
TL;DR: In this paper, the Anderson lattice model for six-fold degenerate Ce ions is used to evaluate electrical resistivity, thermoelectric power, Lorenz number and a.c. conductivity.
Abstract: Transport properties including electrical resistivity, thermoelectric power, Lorenz number and a.c. conductivity are evaluated in an approximate fashion for the Anderson lattice model for six-fold degenerate Ce ions. Coherence (Bloch's theorem) is explicitly included while the effects of intersite interactions which may be responsible for magnetic and superconducting instabilities are neglected. The calculations utilize the AverageT-matrix Approximation (ATA) with the self-consistent Non-Crossing Approximation (NCA) perturbation theory employed to give the single siteT-matrix estimate. The resistivity peaks near the characteristic Kondo temperatureT0, with high temperature logarithmic decrease and low temperatureT2 behavior. The thermoelectric power is positive and similar to the impurity result except for low temperatures; sign changes in the thermopower are in principle possible with momentum dependent hybridization. Frequency and temperature dependent optical conductivity calculations are in qualitative agreement with experimental data, although a suitably defined optical effective mass and scattering rate do not agree at least for large orbital degeneracy. The behavior of these latter quantities is qualitatively different for twofold degeneracy. Unanswered questions arising from the experimental literature are summarized.
95 citations
TL;DR: From studying the transverse momentum distribution in heavy-ion collisions, it is concluded that the nuclear equation of state at high density is softer than that determined previously using the normal Vlasov-Uehling-Uhlenbeck model and is consistent with that from the analysis with a momentum-dependent potential.
Abstract: The previously derived relativistic Vlasov equation from the Walecka model is generalized to include both a collision term and the self-interaction of the scalar meson. From studying the transverse momentum distribution in heavy-ion collisions, we conclude that the nuclear equation of state at high density is softer than that determined previously using the normal Vlasov-Uehling-Uhlenbeck model and is consistent with that from the analysis with a momentum-dependent potential. We have also found that in relativistic model the magnitude of the transverse momentum from heavy-ion collision is more sensitive to the value of the nucleon effective mass at saturation density than the value of the compressibility at this density.
94 citations
TL;DR: In this article, the authors derived a microscopic model representing a coupled system of spin degrees of freedom on O sites and a low concentration of mobile holes, assuming that the predominant charge carriers in superconducting cooper oxides are holes on the O sites.
94 citations
TL;DR: In this paper, the authors present a general theoretical analysis of the problem of mass transfer during the drying of shrinking multiphase systems, and derive a complete theory for drying of cellular materials in the stage during which the cellular structure prevails.
87 citations
TL;DR: In this paper, it was shown that while the superlattice becomes semimetallic with increasing valence-band offset, it reverts to semiconducting behavior as the offset is increased yet further.
Abstract: The valence-band-offset controversy in HgTe/CdTe superlattices can be simply resolved. It is shown that, while the superlattice becomes semimetallic with increasing valence-band offset, it reverts to semiconducting behavior as the offset is increased yet further. The observed electron-cyclotron mass and the band gap can be better explained for the offset of 350 meV measured by photoemission than for the smaller offset \ensuremath{\sim}40 meV which coincidentally is also in fair agreement with the magneto-optical data.
82 citations
TL;DR: In this article, the effect of various material parameters on the calculated velocity is assessed by varying each parameter independently by ±20% and the combined effects of a greater central valley effective mass and a larger phonon energy in AlGaAs result in a greater threshold field.
Abstract: We present ensemble Monte Carlo calculations of the steady‐state electron drift velocity as a function of applied electric field in Al0.32 Ga0.68 As. The effect of various material parameters on the calculated velocity is assessed by varying each parameter independently by ±20%. It is found that both the optical phonon energy and intervalley separation energy alter the peak electron velocity greatly. Variations in the dielectric constants and central valley effective mass have little effect upon the peak drift velocity, but act to alter the threshold electric field. It is further found that the threshold electric field is greater in Al0.32Ga0.68As than in GaAs even though the central‐to‐satellite valley separation energy is less in AlGaAs. The combined effects of a greater central valley effective mass and a larger phonon energy in AlGaAs result in a greater threshold field. Finally, we present sets of material parameters useful in Monte Carlo models for both GaAs and AlGaAs.
TL;DR: In this article, the authors have grown pseudomorphic InxGa1−xAs/In0.52Al0.48As modulation-doped heterostructures by molecular beam epitaxy under carefully controlled growth conditions.
Abstract: We have grown pseudomorphic InxGa1−xAs/In0.52Al0.48As modulation‐doped heterostructures by molecular‐beam epitaxy under carefully controlled growth conditions. Mobilities as high as 13 900, 74 000, and 134 000 cm2/V s are measured at 300, 77, and 4.2 K in a heterostructure with x=0.65. Shubnikov–de Haas measurements indicate that the change in the effective mass with increasing In is not significant and is not responsible for the enhancement in mobilities. We believe that the improvement results from reduced alloy scattering, reduced intersubband scattering, and reduced impurity scattering, all of which result from a higher conduction‐band offset and increased carrier confinement in the two‐dimensional electron gas. The high‐field electron velocities have been measured in these samples using pulsed current‐voltage and pulsed Hall measurements. A monotonic increase in velocities is observed both at 300 and 77 K with an increase of In content in the channel. Velocities of 1.55×107 and 1.87×107 cm/s are meas...
TL;DR: In this paper, local density approximation (LDA) calculations for the Fermi surface extremal cross-sectional areas of UPt{sub 3} are presented and compared to deHaas-van Alphen experiments of Taillefer et al.
TL;DR: In this article, the electron effective mass in the InxGa1−xAs conduction channel of strained AlGaAs/InGaA/GaAs pseudomorphic structures was measured using far-infrared cyclotron resonance techniques at 4.2 K.
Abstract: Electron effective mass in the InxGa1−xAs conduction channel of strained AlGaAs/InGaAs/GaAs pseudomorphic structures is measured using far‐infrared cyclotron resonance techniques at 4.2 K. The measured cyclotron mass is heavier than the conduction‐band‐edge mass in bulk InxGa1−xAs. This result is explained by the large two‐dimensional electron density realized in the structure, and the lattice strain that exists in the InxGa1−xAs layer.
TL;DR: In this article, the effective mass Hamiltonian H = 1/2malpha pmbeta pmalpha +Vc+ upsilon for non-homogeneous semiconductors is studied.
Abstract: The effective-mass Hamiltonian H=1/2malpha pmbeta pmalpha +Vc+ upsilon for non-homogeneous semiconductors is studied. Here m is the position-dependent effective mass, 2 alpha + beta =-1. Vc is the position-dependent conduction band edge and upsilon is a localised potential. Through an exact model calculation the authors show that when effective-mass theory is applicable, alpha =0 and beta =-1,.
TL;DR: In this paper, the stability of uniform nuclear matter in the relativistic Hartree approximation to the Walecka model is investigated by calculating the meson propagators in the one-loop approximation.
TL;DR: In this article, the energy levels of the GaAsn(AlAs)n [001] superlattices (n=1,2) with those of the disordered Ga0.5Al 0.5As alloy were compared.
Abstract: Using self‐consistent electronic structure calculations we contrast the energy levels of the ultrathin (GaAs)n(AlAs)n [001] superlattices (n=1,2) with those of the disordered Ga0.5Al0.5As alloy and a long period (n→∞) superlattice. Conventional Kronig–Penney and effective mass models suggest that, because of the relatively light electron effective masses and small barrier heights, only delocalized superlattice conduction states would exist in the n=1 limit. We find a number of such conventional ‘‘averaging states’’ (delocalized on both sublattices). In addition, we also find states localized on a single sublattice. For small n’s, the latter are divided into two classes: (i) ‘‘repelling states’’ (distinct alloy states which fold in the superlattice into states of identical symmetry, which, in turn, repel each other and tend to localize), and (ii) ‘‘segregating states’’ (a pair of localized states Ψα and Ψβ, where symmetry compels Ψα to have a vanishing angular momentum component l on a subset α of unit cel...
TL;DR: In this paper, a canonical transformation of the Hamiltonian of a neutral system of charged particles in a homogeneous magnetic field is transformed into the sum of an internal Hamiltonian, a CM kinetic energy operator and a term coupling the internal and CM motions.
Abstract: With a canonical transformation, the Hamiltonian of a neutral system of charged particles in a homogeneous magnetic field is transformed into the sum of an internal Hamiltonian, a CM kinetic energy operator and a term coupling the internal and CM motions. When the magnetic quantum number m of a hydrogen atom state differs from zero, its binding energy is qualitatively affected by the existence of a transverse motion, even a very small one. The number of bound states with a given m not=0 becomes finite and vanishes beyond a critical magnetic field. For any m, the binding energies are reduced by a transverse collective energy which is conveniently expressed as a function of an effective mass. Several effective masses are calculated with a second-order perturbation method in the strong-field region.
TL;DR: In this paper, the energy and the effective mass of an electron in a quantum-well wire of GaAs surrounded by Ga 1− x Al x As was calculated using a variational approach.
TL;DR: In this paper, the authors calculated the valence-subband structures of GaAs−Ga1−xAlxAs quantum wells based on the bond-orbital model and found that the Al composition has a strong effect on the hole effective mass.
Abstract: Valence‐subband structures of GaAs‐Ga1−xAlxAs quantum wells growth in the [001], [111], and [110] directions are calculated based on the bond‐orbital model. The effective mass for the first subband in (111)‐oriented quantum wells is found to be substantially smaller than that in (001)‐oriented quantum wells for well widths narrower than 70 A. The subband structures of (110)‐oriented quantum wells display large anisotropy, with effective masses along two different in‐plane directions ([001] and [110]) differing by almost one order of magnitude. It is also found that the Al composition has a strong effect on the hole effective mass. Implications of our results in device applications are also discussed.
TL;DR: In this paper, a Drude-like spectrum was found for the first time in metallic BEDT-TTF 2 I 3, an organic superconductor, at temperatures over 16-295 K.
Abstract: Polarized reflectance spectra in the region from 720 cm -1 to 25000 cm -1 were measured on the single crystal of θ-(BEDT-TTF) 2 I 3 , an organic superconductor, at temperatures over 16–295 K. A Drude-like spectrum was found for the first time in metallic BEDT-TTF salts. This characteristic spectrum was attributed to the unique structure of the θ-type crystal. The curve-fitting analysis of the spectra gave the plasma frequencies (ω p ) a =1.05 eV and (ω p ) c =0.73 eV at 16 K, from which the anisotropic effective masses were evaluated to be m a * =1.5 m e and m c * =3.0 m e . The transfer integrals and other band parameters of the tight-binding band were directly derived from the analysis of the optical data. The transfer integrals thus obtained are t a =0.080 eV and t c =0.046 eV. These results are to be compared with the calculated band structure.
TL;DR: In this article, the authors calculate exciton binding energies and oscillator strengths in GaAs-GaAlAs quantum wells, starting from the subband structure which contains valence band mixing.
Abstract: The authors calculate exciton binding energies and oscillator strengths in GaAs-GaAlAs quantum wells, starting from the subband structure which contains valence band mixing. The effect of Coulomb coupling between excitons belonging to different subbands is calculated and is shown to be important: the strongest interaction is with the exciton continuum. Calculated binding energies agree within 1 meV with photoluminescence excitation experiments. It is shown that parity forbidden excitons have zero oscillator strength even when valence band mixing is included. Therefore, some transitions reported in the literature cannot be ground-state excitons, and are reinterpreted here as excitons in excited states.
TL;DR: In this paper, the binding energies and dispersions of the n = 1 and n = 2 members of the image potential series of surface state on Cu(111) are measured using the technique of angle-resolved two-photon photoelectron spectroscopy.
TL;DR: In this paper, the Brueckner-Hartree-Fock approximation was extended to include single-particle correlations, and a liquid-vapor phase transition was observed, wtih a critical temperature of about 20 MeV.
TL;DR: In this article, the authors generalize a result of Cohen and de Felice (1984) and show how rotational effects can be taken into account by incorporating the rotational contribution at all.
Abstract: The expressions for the effective mass of rotating spacetimes existing in the literature do not incorporate the rotational contribution at all. The authors generalise a result of Cohen and de Felice (1984) and show how rotational effects can be taken into account.
TL;DR: In this article, the saturation point in the vicinity of the Fermi momentum was studied in the framework of an approximation scheme which includes single-particle correlations, and the Hugenholtz-Van Hove theorem was well satisfied, in contrast with standard Brueckner calculations.
TL;DR: In this paper, the 10-micron intersubband absorption in quantum wells made of the silicon-based system, Si/Si(1-x)Ge(x), has been calculated and the necessary details of the effective mass anisotropy are included in the present analysis.
Abstract: The 10-micron intersubband absorption in quantum wells made of the silicon-based system, Si/Si(1-x)Ge(x), has been calculated. The necessary details of the effective-mass anisotropy are included in the present analysis. It is found that it is readily possible to achieve an absorption constant of order of 10,000/cm in Si quantum wells with current doping technology. For 110-line and 111-line growth directions, a further advantage of Si quantum wells is pointed out, namely, an allowed absorption at normal incidence due to the anisotropic effective mass in Si.
TL;DR: In this paper, a variation of the temperature of the superconducting transition is observed in the upper critical fields Hc2 and proton NMR relaxation measurements at temperatures below TC.
TL;DR: In this article, the authors investigated theoretically the effective electron mass in ternary chalcopyrite semiconductors at low temperatures on the basis of a newly derived dispersion relation of the conduction electrons under cross fields for the more generalized case which occurs from the consideration of various types of anisotropies in the energy spectrum.
Abstract: An attempt is made to investigate theoretically the effective electron mass in ternary chalcopyrite semiconductors at low temperatures on the basis of a newly derived dispersion relation of the conduction electrons under cross fields for the more generalized case which occurs from the consideration of the various types of anisotropies in the energy spectrum. It is found, taking degeneraten-CdGeAs2 as an example, that the effective electron mass at the Fermi level along the direction of magnetic quantization depends on both the Fermi energy and the magnetic quantum number due to the combined influence of the crystal field splitting parameter and the anisotropic spin-orbit splitting parameter respectively, resulting in different effective masses at the Fermi level corresponding to different magnetic sub-bands. It is also observed that the same mass at the Fermi level in the direction normal to both magnetic and electric fields also varies both with Fermi energy and magnetic sub-band index, and the characteristic feature of cross-fields is to introduce the index-dependent oscillatory mass anisotropy. The theoretical results are in good agreement with the experimental observations as reported elsewhere.