摘要:

AbstractThe influence of electron correlations on the temperature dependent electronic structure of ferromagnetic f.c.c. cobalt is investigated by a many‐body evaluation of a generalized model of magnetism. The single‐particle part of the model‐Hamiltonian is taken from an LDA band structure calculation. The interaction part contains two parameters, an intraband Coulomb interactionUand an interband exchangeJ. WithU= 3.5 eV andJ= 0.3 eV the self‐consistent model solution yields a magneticT= 0 moment of about 1.75μBand a Curie temperature of 1375 K. The magnetic behaviour finds a conclusive microscopic explanation by the temperature and density dependent quasiparticle density of states. Typical differences as well as common features in the electronic structures of Fe, Co, and Ni are worked out. Contrary to Ni, no satellite appears in F

ISSN:0370-1972    

DOI:10.1002/pssb.2221930120

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe contribution of pairs and triads of nearest‐neighbor spins to the spin‐lattice relaxation of magnetization is evaluated in Mn‐based diluted magnetic semiconductors. Modulation of the exchange interaction by lattice vibrations allows transitions in the cluster which change the total magnetization when the Dzyaloshinski‐Moriya interaction is taken into account. Spin‐lattice relaxation rates are calculated for pairs and open triads due to a two‐phonon Orbach process. In Cd1−xMnxTe it is found that the main contribution to relaxation of magnetization comes from triads. For temperatures ranging from 10 to 35 K and for x between 0.002 and 0.02 relaxation of triads can account very well for the observed relaxation rates, if one assumes rapid spin diffusion. Fitting of the experimental data yields an approximate value of a = J/(dJ/dr) ∼ 0.35 A, where J is the nearest‐neighbors exchange constant and r the Mn‐anion bond length, in good agreement with the expected value for a supere

ISSN:0370-1972    

DOI:10.1002/pssb.2221930121

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe linear optical absorption of dopyballs C60−nXn(X = B or N;n= 1, 2) is studied using the extended Su‐Schrieffer‐Heeger model and the sum‐over‐states approach. Comparing the calculated results C60−nXnwith those of C60, it is shown that the substitutional doping of impurity atoms (B or N) can greatly change the optical properties of the c60system. Many absorption peaks due to substitutional doping appear in the low frequency region. In particular, a remarkable peak is found at the low frequency end in C58X2(1,

ISSN:0370-1972    

DOI:10.1002/pssb.2221930122

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe optical properties of spontaneously ordered GaInP2grown by MOVPE are studied by means of photoluminescence, time‐resolved photoluminescence, and polarization dependent photoluminescence excitation spectroscopy. Ordered samples grown on a substrate which is misoriented 6° toward [111]Bshow clear excitonic features both in luminescence and absorption. In excitation spectra both valence band edges are clearly resolved and are shown to be polarization dependent as predicted by band structure calculations. In these samples an additional non‐excitonic low‐energy photoluminescence emission is observed the peak energy of which depends strongly on excitation density and temperature and which shows extremely long luminescence lifetimes. A density of states model for ordered GaInP2is proposed which allows to explain the results obtained in the last few years. The density of states model is discussed with respect to the microstructure of the ordered alloy as known from TEM investig

ISSN:0370-1972    

DOI:10.1002/pssb.2221930123

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe microscopic dielectric function of silver is investigated in the framework of the time‐dependent density‐functional theory underlying a spline augmented plane‐wave band calculation. A reasonable overall agreement is found when comparing our results with experimental data. Small systematic errors in the position of the peaks can be ascribed to the local density approximation. It is shown that in the long‐wave limit a zero of the diagonal element corresponds to a plasmon excitation. The frequency of the q = 0 plasmon excitation agrees quite well with its experimental value. No plasmon excitation can be found even for small values of the propagation

ISSN:0370-1972    

DOI:10.1002/pssb.2221930124

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe spectroscopic and dynamic studies of the Tm3+doped cadmium fluoride show the existence of a 450 nm emission (1D2→3F4transition), excited around 650 nm (3H4→1D2transition) by a tunable laser. The presence of a power threshold for the density of excitation allows to establish that the upconversion mechanism is the photon‐avalanche pr

ISSN:0370-1972    

DOI:10.1002/pssb.2221930125

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractPulsed electron beam excitation of 0.45 to 0.7% CsF doped in rare gas matrices at 5 K leads to emission bands at 196.5 nm (FWHM 9.6 nm) and 227 nm (FWHM 15 nm) in Ne and at 211.2 nm in Ar. The short‐wavelength bands are assigned to B2→ X2− transitions in the ionic Cs2+F−excimer on the basis of transition energies, lineshapes, and the efficiency of Cs2+F−ionization by energy transfer from the host. The long‐wavelength band in Ne corresponds to a C2II‐A2II transition. The 196.5 nm band provides a large cross section for stimulated emission of 2.5 × 10−16cm2. The red shifts of 0.4 and 0.8 eV of the B → X emission in Ne and Ar, respectively, are discussed in terms of solvation of the Cs2+F−ion and of its dipole moment. Optimal concentrations are similar to those obtain

ISSN:0370-1972    

DOI:10.1002/pssb.2221930126

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe photoluminescence (PL) properties of ZnSe epitaxial layers grown by metal‐organic vapor phase epitaxy are investigated. A correlation between the electron‐hole plasma (EHP) band position and the PL intensity is found and on this basis the nonequilibrium carrier lifetime τ and the PL efficiency η are estimated in the ZnSe layers: τ = 10−9to 10−11s, η = 0.1 to 0.001%. It is shown that these parameters decrease with decreasing layer thickness and with increasing concentration of contaminations and native defects. The influence of the excitation level and temperature on the intensity and peak position of the band at 472 nm in ZnSe: N and the band at 620 nm in undoped ZnSe epilayers at 78 K grown at temperatures ofTD>500 °C are studied. It is supposed that these bands are due to recombinations described in the configurational coor

ISSN:0370-1972    

DOI:10.1002/pssb.2221930127

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractA theory of cyclotron resonance (CR) for type‐II (InAs/GaSb) superlattices based on the 8 × 8k · pmatrix Hamiltonian (Bodnar model), which includes the effect of electron‐hole interactions is developed. In this model, the effect of nonparabolicity and anisotropy is included. Using linear response theory, an expression for the cyclotron absorption coefficient is obtained. It is predicted for the first time that due to the anisotropy of the band structure, the CR transitions are sensitive to the orientation of the sample relative to the growth direction. This prediction agrees with the experiments on a qualitative basis. In addition it is predicted that as the strength of the magnetic field increases the square of the matrix elements of the CR transitions also increases. The present theory can also be applied to study the interband magneto‐optical transitions along with the intraband tran

ISSN:0370-1972    

DOI:10.1002/pssb.2221930128

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

ISSN:0370-1972    

DOI:10.1002/pssb.2221930101

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY