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Showing papers on "Effective mass (solid-state physics) published in 1987"


Journal ArticleDOI
TL;DR: In this article, it was shown that superlattices made of InAs−Ga1−xInxSb x∼0.4 have favorable optical properties for infrared detection.
Abstract: We show that strained type II superlattices made of InAs‐Ga1−xInxSb x∼0.4 have favorable optical properties for infrared detection. By adjusting the layer thicknesses and the alloy composition, a wide range of wavelengths can be reached. Optical absorption calculations for a case where λc∼10 μm show that near threshold the absorption is as good as for the HgCdTe alloy with the same band gap. The electron effective mass is nearly isotropic and equal to 0.04 m. This effective mass should give favorable electrical properties, such as small diode tunneling currents and good mobilities and diffusion lengths.

680 citations


Journal ArticleDOI
TL;DR: High-resolution angle-resolved photoemission studies of the surfaces of copper, silver, and gold are reported which investigate in detail the properties of the intrinsic surface states located in the projected sp-band gaps at the center of the surface Brillouin zones.
Abstract: High-resolution angle-resolved photoemission studies of the (111) surfaces of copper, silver, and gold are reported which investigate in detail the properties of the intrinsic surface states located in the projected sp-band gaps at the center of the surface Brillouin zones. Accurate two-dimensional energy dispersion relations are reported for each surface state and are quantified in terms of effective masses at the surface Brillouin-zone center. The masses for the three metals are found to be remarkably similar when normalized to the effective mass of the lower edge of the bulk continuum. The decay length of the surface state wave function into the surface was determined for all three surfaces. These results are expressed in terms of an effective mass of the complex dispersion relation within the projected band gap. In accord with our previous results on the copper state, these effective masses are found to be anomalously large by approximately a factor of 2 relative to expectations based on effective mass theory coupled to first-principles bulk band calculations. An explanation of this anomaly involving the nonorthogonality of effective-mass-theory-derived states is explored. All experimental results are compared to the predictions of recent self-consistent surface electronic structure calculations for these surfaces.

275 citations


Journal ArticleDOI
TL;DR: Valence subbands of uniaxially stressed GaAs-Ga1-xAlxAs quantum wells are found by solving exactly the multiband effective-mass equation for the envelope function and Resonances are shown to arise and are due to the degeneracy of discrete levels with states of the continuum at different values of k?
Abstract: Valence subbands of uniaxially stressed GaAs-Ga1-xAlxAs quantum wells are found by solving exactly the multiband effective-mass equation for the envelope function; as in the particle in a box problem, we first solve the effective-mass equation in each bulk material, and then we impose boundary conditions on the linear combinations of bulk solutions Discrete symmetries of the effective-mass Hamiltonian are used to decouple the spin-degenerate subbands; the energy levels are obtained as the zeros of an 8A—8 determinant The functional form of the wave functions is given analytically, and is used in order to discuss the heavy-hole light-hole mixing at finite values of the in-plane vector k?; the mixing greatly increases when the applied stress reduces the energy separation at k?=0 Resonances are shown to arise and are due to the degeneracy of discrete levels with states of the continuum at different values of k? © 1987 The American Physical Society

147 citations


Journal ArticleDOI
TL;DR: The characteristics of a stiff equation of state can be obtained with a much softer compressibility in 400 MeV/nucleon heavy ion collisions.
Abstract: We examine the influence of momentum-dependent interactions on the momentum flow in 400 MeV/nucleon heavy ion collisions. Choosing the strength of the momentum dependence to produce an effective mass ${m}^{\mathrm{*}}$=0.7m at the Fermi surface, we find that the characteristics of a stiff equation of state can be obtained with a much softer compressibility.

144 citations


Journal ArticleDOI
TL;DR: In this paper, a double-barrier resonant tunneling structure is proposed to describe the experimental currentvoltage curves and the space-charge formation, both in the electrodes and in the well.
Abstract: The standard model of double-barrier resonant tunneling structures inadequately describes the experimental current-voltage curves. When applied to experiments on resonant tunneling in quantizing magnetic fields, it leads to incorrect values of the electron effective mass in the well. We show that the space-charge formation, both in the electrodes and in the well, not considered previously, is, in fact, very important. We present a model which takes into account these effects. The calculations, based on our model, are in good agreement with the experimental results.

141 citations



Journal ArticleDOI
TL;DR: In this article, the functional integral of the polaron is defined as the inverse of the effective diffusion coefficient of the random walk, and an upper bound on the effective stiffness is derived.

100 citations


Journal ArticleDOI
TL;DR: In this paper, zero and finite temperature contributions of ground state correlations to the nuclear mean field are studied in nuclear matter at normal density, where the framework is the nonrelativistic hole line expansion with the Paris potential as the bare NN interaction.

98 citations


Journal ArticleDOI
TL;DR: In this paper, low-temperature, high-field deHaas-van Alphen measurements are presented which show that the conduction-electron mass in the Kondo lattice decreases strongly with field.
Abstract: Low-temperature, high-field deHaas--van Alphen measurements are presented which show that the conduction-electron mass in the Kondo lattice ${\mathrm{CeB}}_{6}$ decreases strongly with field. This field dependence is consistent with recent specific-heat results. The geometry of the Fermi surface does not depend on field. Thus we observe a reduction in the many-body enhancement of the electronic density of states at the Fermi energy which is described by a change of the itinerant-electron mass alone; the number of particles and the occupation of states in k space remain unchanged. We argue that ${\mathrm{CeB}}_{6}$ represents a different limit of heavy-fermion behavior as compared to ${\mathrm{UPt}}_{3}$.

84 citations


Journal ArticleDOI
TL;DR: In this article, a new resonant tunneling process is discussed theoretically, which relies on elastic intervalley transfers between different band minima, e.g., between Γ and X minima in a GaAs•AlAs system.
Abstract: A new resonant tunneling process is discussed theoretically. The process relies on elastic intervalley transfers between different band minima, e.g., between Γ and X minima in a GaAs‐AlAs system. Single layer GaAs‐AlAs‐GaAs heterostructures are analyzed. An effective mass envelope function approach is used, and a delta‐function transfer potential at heterointerfaces is employed. A resonance in the transmission coefficient is clearly seen, which gives rise to a negative differential resistance region in the current‐voltage characteristic.

79 citations


Journal ArticleDOI
TL;DR: The electrical resistivity and the Seebeck coefficient of thermally evaporated thin bismuth films of thicknesses from 300 to 1900 A\r{} have been measured and the latter is negative and its magnitude is found to increase initially with increasing temperature, reach a maximum, and then decrease with a further rise in temperature.
Abstract: The electrical resistivity and the Seebeck coefficient of thermally evaporated thin bismuth films of thicknesses from 300 to 1900 A\r{} have been measured in the temperature range 300--470 K. The latter is negative and its magnitude is found to increase initially with increasing temperature, reach a maximum, and then decrease with a further rise in temperature. The temperature at which the Seebeck coefficient is maximum is found to be thickness dependent, decreasing with increasing thickness. The observed dependence is explained by considering that the Fermi energy is temperature dependent. Bismuth films show a negative temperature coefficient of resistivity. The thickness dependence of the electrical resistivity and the Seebeck coefficient of simultaneously prepared films are analyzed using the newer effective mean-free-path model. From the analysis, important material constants like the mean free path, the electron concentration, and the effective mass of electrons have been evaluated.

Journal ArticleDOI
TL;DR: In this paper, the spectral properties of AlxGa1−xAs/GaAs coupled quantum well structures were investigated under the Stark perturbation, and it was shown that positive energy shifts and high sensitivity to electric fields have been interpreted as evidence of well coupling.
Abstract: Optical spectra near the band edges of AlxGa1−xAs/GaAs coupled quantum well structures are found to exhibit rich structure. Under the Stark perturbation, these transitions have behavior remarkably different from those associated with single quantum wells. Positive energy shifts and high sensitivity to electric fields have been observed and interpreted as evidence of well coupling. Results of a simple numerical calculation support this interpretation.

Journal ArticleDOI
TL;DR: The results of the Gutzwiller approach to a Hubbard lattice-gas model with a variable density of particles is used to describe the pressure dependence of thermodynamic properties of the ground state of normal liquid $^{3}\mathrm{He}$.
Abstract: The results of the Gutzwiller approach to a Hubbard lattice-gas model with a variable density of particles is used to describe the pressure dependence of thermodynamic properties of the ground state of normal liquid $^{3}\mathrm{He}$. The molar volume of the liquid is given by that of the underlying lattice and the filling factor n=1-\ensuremath{\delta} of the band, where \ensuremath{\delta} describes the deviation from half-filling. If the lattice is taken as incompressible, one finds that there exists a critical pressure at which a transition to a localized state occurs. The transition is accompanied by a disappearance of \ensuremath{\delta}, i.e., the transition only takes place at exactly half-filling. As the transition is approached, \ensuremath{\delta} and the density of doubly occupied sites are found to scale. The pressure dependence of the effective mass, the spin susceptibility and the compressibility is calculated. In a second model, the lattice is assumed to be compressible, shifting the critical pressure to much higher values. The on-site repulsion U is related to the microscopic soft-core potential ${f}_{0}^{s}$(r), which allows one to calculate the pressure dependence of the effective mass and the spin susceptibility. The absence of a localization transition for pressures of the order of the melting pressure of $^{3}\mathrm{He}$ leads to a smooth pressure dependence of the calculated quantities which are qualitatively borne out by experiment.

Journal ArticleDOI
TL;DR: In this paper, the authors used the optical matrix elements and the band structure computed by the k-cdot p method within the envelope function approximation to study gain in a quantum well.
Abstract: Gain in a quantum well is studied by using the optical matrix elements and the band structure computed by the k \cdot p method within the envelope function approximation. Due to band mixing, the k \cdot p method gives nonparabolic bands which affect both the minimum confinement energies and the density of states functions. The density of states functions are found to differ considerably from the simple step-like shape computed from the band edge effective masses. The band mixing also results in large differences in the momentum vector dependence of the matrix elements, and moreover, some of the transitions which were previously assumed to be forbidden become partially allowed. The quantum well gain spectra calculated by the k \cdot p method and the k -selection rules clearly show the effects of band mixing both in shape and in peak magnitude. These results are considerably different than those obtained from the conventional methods which consider an effective mass electron (or hole) in a finite one-dimensional potential well with parabolic bands and with matrix elements which have constant total magnitude. A practical conclusion which is reached from these comparisons is that the threshold excitation in a quantum well laser is found to be strongly underestimated if band mixing effects are ignored.

Journal ArticleDOI
TL;DR: In this article, the conduction bands in GaAs and In have been studied very accurately through the cyclotron resonance over a wide range of energies using the photoconductive detection technique.
Abstract: The conduction bands in GaAs and In have been studied very accurately through the cyclotron resonance over a wide range of energies using the photoconductive detection technique. Pronounced band non-parabolicity has been measured in GaAs. Values for the band-edge masses of 0.0660 m0 and 0.07927 m0 respectively have been determined. A five-level k.p model of the band structure in the presence of a magnetic field has been used to describe the data where resonant and non-resonant polaron contributions to electron energies are included in the theory. The non-parabolicity and spin-doublet splitting of the cyclotron resonance are well described by the employed formalism in both materials and the theory also gives a reasonable account of the anisotropy of the band in GaAs. The fit to experimental data allowed the authors to determine the matrix element of momentum Q between the higher conduction and valence bands in both materials.

Journal ArticleDOI
TL;DR: In this article, the ground-state heavy-hole exciton states in AlxGa1−xAs graded-gap quantum well structures with an electric field perpendicular to the layer have been calculated.
Abstract: Exciton states in AlxGa1−xAs graded‐gap quantum well structures with an electric field perpendicular to the layer have been calculated. The calculations show that, for the ground‐state heavy‐hole exciton in this quantum well structure, the dependence of Stark shift and the oscillator strengths on the external electric field is quite different from the case of the usual square‐shaped quantum well structure, whereas for the ground‐state light‐hole exciton there is no significant difference between these two quantum well structures. These results can be interpreted in terms of the difference between the heavy‐hole effective mass and the light‐hole one.

Journal ArticleDOI
TL;DR: In this article, the resonant tunneling condition and transmission coefficient for a symmetrical one-dimensional rectangular double-barrier structure under the assumption of the tunneling effective mass were derived theoretically.
Abstract: The resonant tunneling condition and transmission coefficient are derived theoretically for a symmetrical one-dimensional rectangular double-barrier structure under the assumption of the tunneling effective mass. They are given in analytical form, which has been overlooked. The energy variation of the transmission coefficient of electrons is shown for an ABABA-type and an ABCBA-type potential cases.

Journal ArticleDOI
TL;DR: In this article, the temperature dependence of the electron mobility in the crystallographic directions a and c has been quantitatively interpreted through Fivaz-Schmid and Brooks-Herring models for homopolar optical phonon and ionized impurities scattering, respectively, yielding the energy of the phonon mode and the electron-phonon coupling constant.
Abstract: Impurity levels and electron scattering mechanisms in bismuth sulfide have been investigated by means of resistivity and Hall-effect measurements in the 30--500-K temperature range. Lattice scattering is predominant in this range and the temperature dependence of the electron mobility, in the crystallographic directions a and c, has been quantitatively interpreted through Fivaz-Schmid and Brooks-Herring models for homopolar optical phonon and ionized impurities scattering, respectively, yielding the energy of the phonon mode (\ensuremath{\Elzxh}\ensuremath{\omega}=14 meV) and the electron-phonon coupling constant (${g}^{2}$\ensuremath{\gtrsim}0.4). The density-of-states effective mass in the conduction band has also been determined from Seebeck-effect measurements at room temperature.

Journal ArticleDOI
TL;DR: In this paper, a chiral field theory for nuclear matter purely based on fermionic degrees of freedom is presented, and the Nambu-Jona-Lasinio symmetry breaking mechanism is applied in order to obtain a nonvanishing density dependent effective mass of the nucleon.

Journal ArticleDOI
TL;DR: In this article, an effective dipole theory is presented to estimate the band lineups at the interface of a lattice matched or nearly matched semiconductor heterojunction, which causes additional shift ΔEv in the difference of the band edges.
Abstract: An effective dipole theory is presented to estimate the band lineups at the interface of a lattice‐matched or nearly matched semiconductor heterojunction. The theory is based on the formation of an effective dipole at the interface which causes additional shift ΔEv in the difference of the band edges. A set of equations are derived from which δEv can be solved iteratively. The calculation requires the values of the top of the valence band and several bulk band‐structure parameters of the constituent semiconductors as input. The dipole effect is evaluated by considering the charge transfer induced by the penetration of the effective mass electrons representing the bulk band states into the quantum barrier of the neighboring semiconductor. The theory is applied to predict the band offset values of more than 100 heterojunctions involving group IV, III‐V, and II‐VI semiconductors. Of the 30 heterojunctions for which the experimental data have been reported, the predicted values differ from the data by only ab...

Journal ArticleDOI
TL;DR: In this article, the experimental dynamic and static longitudinal structure factors of 12 C, 40 Ca and 56 Fe were investigated with a semiclassical RPA theory and the ph interaction was linked at zero momentum to the nuclear compression modulus and symmetry energy.

Journal ArticleDOI
TL;DR: In this article, a method of determining the values of main parameters such as the effective mass, the Fermi energy, and the coherence length for the new high Tc superconductors is developed.

Journal ArticleDOI
TL;DR: In this paper, a detailed analysis of the acoustic phonon emission spectrum of a heated 2DEG in a (0 0 1) n-Si inversion layer, when a quantizing magnetic field B is applied perpendicular to the layer, is given.

Journal ArticleDOI
TL;DR: In this article, a theoretical study of the barrierless electronic relaxation in solution is presented, where the authors show that the long time decay rate is independent of the excitation wavelength although the average rate (so the quantum yield) show a strong dependence.
Abstract: We report a theoretical study of the barrierless electronic relaxation in solution. The existing theoretical models are divided into two classes: (A) Instantaneous death models where the excited state decays with unit probability as soon as it attains certain critical conformations, and (B) finite decay models, where the decay from the critical geometries occur at a finite rate (=k0). All the models belonging to class (A) predict inverse friction (ζ) dependence of the nonradiative decay rate if the radiative relaxation is neglected. These models predict that the long time decay rate is independent of the excitation wavelength although the average rate (so the quantum yield) show a strong dependence. The relaxation behavior of models (B) is controlled by the dimensionless parameter k0(=k0ζ/ω2μ, where ω is the frequency of the excited state surface and μ is the effective mass of the reactive motion). A fractional friction dependence of the long time rate is obtained at low to intermediate values of k0, bu...

Journal ArticleDOI
TL;DR: In this paper, a previously developed dispersion relation approach is used to calculate the shell-model potential in the case of neutrons in 208Pb, in the energy domain (-50 MeV, 0).

Journal ArticleDOI
TL;DR: A comparison to theoretical models reveals the necessity of taking the nonparabolicity of the conduction band as well as of all the valence subbands into account, and the best theoretical description is given by using a conduction-band offset =500 meV as determined by capacitance-voltage measurements in the literature.
Abstract: The subband structure of ${\mathrm{Ga}}_{0.47}$${\mathrm{In}}_{0.53}$As/${\mathrm{Al}}_{0.48}$${\mathrm{In}}_{0.52}$As multi-quantum-well heterostructures (MQWH's) lattice matched to InP, grown by molecular-beam epitaxy, was determined by absorption and magnetoabsorption experiments for well widths ranging from 2.3 to 13.8 nm. A comparison to theoretical models (parabolic single-band and coupled six-band envelope-function approximations) reveals the necessity of taking the nonparabolicity of the conduction band as well as of all the valence subbands into account. The equal values for the reduced effective mass and the electron effective mass, obtained by Shubnikov\char21{}de Haas and cyclotron-resonance experiments, show that the highest valence-subband mass is much larger than the theoretical assumption from decoupled valence subbands. In view of the complete subband structure the best theoretical description is given by using a conduction-band offset \ensuremath{\Delta}${E}_{c}$=500 meV as determined by capacitance-voltage measurements in the literature. For this value the calculated subband transition energies are about 10% higher than the experimental results.

Journal ArticleDOI
TL;DR: In this paper, an attempt was made to investigate theoretically the effective electron mass in ultrathin films of ternary chalcopyrate semiconductors in the presence of crossed electric and magnetic fields on the basis of a newly derived E-k dispersion relation of the conduction electrons.
Abstract: An attempt is made to investigate theoretically the effective electron mass in ultrathin films of ternary chalcopyrate semiconductors in the presence of crossed electric and magnetic fields on the basis of a newly derivedE-k dispersion relation of the conduction electrons, which includes various types of anisotropies in the energy spectrum. It is found, takingn-CdGeAs2 as an example, that the effective electron mass at the Fermi level depends on the Fermi energy and the magnetic and size quantum numbers, respectively, which is a characteristic feature of cross-fields. It is also observed that the crystal field parameter effectively enhances the numerical magnitude of the effective Fermi level mass. The corresponding results for isotropic parabolic energy bands are also obtained from the expressions derived.


Journal ArticleDOI
TL;DR: The nearly half-filled Hubbard model with strong on-site repulsion is used as a model for the recently discovered copper oxide high-temperature superconductors, and the mechanism is very different from the BCS mechanism.
Abstract: The nearly half-filled Hubbard model with strong on-site repulsion is used as a model for the recently discovered copper oxide high-temperature superconductors. The onset of superconductivity upon doping the half-filled lattice of La$_{2}\mathrm{Cu}$${\mathrm{O}}_{4}$ is explained in terms of the Bose-Einstein condensation of effective mass $O({m}_{e})$. These holes move freely over an antiferromagnetic background. The mechanism is very different from the BCS mechanism. A fit to data is obtained by adjusting the interplane hopping amplitude, which turns out to be extremely small, though necessary.

Journal ArticleDOI
TL;DR: In this paper, an angle-resolved two-photon photoelectron spectroscopy has been used to study the normally unoccupied band structure of Pd(111), where photoemission features are studied as functions of excitation photon energy hν, polarization state, and emission angle.
Abstract: Angle‐resolved two‐photon photoelectron spectroscopy has been used to study the normally unoccupied band structure of Pd(111). Photoemission features are studied as functions of excitation photon energy hν, polarization state, and emission angle. Below hν=4.9 eV, photoemission is dominated by excitation of bulk states near the Fermi level of Λ3 symmetry through Λ1 excited states between the Fermi and vacuum level. The kinetic energy of the corresponding spectral peak is found to increase according to 2 hν−Φ, where Φ is the Pd(111) work function. At hν=4.9 eV, a surface state with 0.65±0.1 eV binding energy is found. The dispersion of this state with k∥ is well‐described by an effective mass m* equal to the free electron mass me. This state is assigned as the n=1 member of the image potential series of states. The relationship between the dispersion of this state and its position in the (111) projected bulk band gap is discussed.