Showing papers on "Electronic band structure published in 1988"

Diluted magnetic semiconductors

Abstract: We review the physical properties of diluted magnetic semiconductors (DMS) of the type AII1−xMnxBVI (e.g., Cd1−xMnxSe, Hg1−xMnxTe). Crystallographic properties are discussed first, with emphasis on the common structural features which these materials have as a result of tetrahedral bonding. We then describe the band structure of the AII1−xMnxBVI alloys in the absence of an external magnetic field, stressing the close relationship of the sp electron bands in these materials to the band structure of the nonmagnetic AIIBVI ‘‘parent’’ semiconductors. In addition, the characteristics of the narrow (nearly localized) band arising from the half‐filled Mn 3d5 shells are described, along with their profound effect on the optical properties of DMS. We then describe our present understanding of the magnetic properties of the AII1−xMnxBVI alloys. In particular, we discuss the mechanism of the Mn++‐Mn++ exchange, which underlies the magnetism of these materials; we present an analytic formulation for the magnetic susc...

Monte carlo analysis of electron transport in small semiconductor devices including band-structure and space-charge effects

Abstract: The physics of electron transport in Si and GaAs is investigated with use of a Monte Carlo technique which improves the "state-of-the-art" treatment of high-energy carrier dynamics. (1) The semiconductor is modeled beyond the effective-mass approximation by using the band structure obtained from empirical-pseudopotential calculations. (2) The electron-phonon, electron-impurity, and electron-electron scattering rates are computed in a way consistent with the full band structure of the solid, thus accounting for density-of-states and matrix-element effects more accurately than previous transport formulations. (3) The long-range carrier-carrier interaction and space-charge effects are included by coupling the Monte Carlo simulation to a self-consistent two-dimensional Poisson solution updated at a frequency large enough to resolve the plasma oscillations in highly doped regions. The technique is employed to study experimental submicrometer Si field-effect transistors with channel lengths as small as 60 nm operating at 77 and 300 K. Velocity overshoot and highly nonlocal, off-equilibrium phenomena are investigated together with the role of electron-electron interaction in these ultrasmall structures. In the systems considered, the inclusion of the full band structure has the effect of reducing the amount of velocity overshoot via electron transfer to upper conduction valleys, particularly at large biases and low temperatures. The reasonableness of the physical picture is supported by the close agreement of the results of the simulation to available experimental data.

Observation of interface band structure by ballistic-electron-emission microscopy.

Abstract: The paper reports an advanced ballistic electron spectroscopy technique that was used to directly measure semiconductor band structure properties at a subsurface interface. Two interface systems having contrasting band structures were investigated by this method: Au-Si and Au-GaAs. It is concluded that the proposed method, based on scanning tunneling microscopy, enables the spatially resolved carrier-transport spectroscopy of interfaces.

Band structure engineering of semiconductor lasers for optical communications

Abstract: Recent advances in epitaxial growth have led to the prospect of artificial modification of the electronic structure or band structure of semiconductor materials. The combination of strain and quantum confinement in the valence band can lead to substantially more favorable energy dispersion relations for laser action than those existing in the natural semiconductor crystal. Numerical results are presented for a series of alloy compositions with a bandgap near the 1.55- mu m optimum wavelength for optical communications. The laser threshold current and the intervalence band absorption can be significantly diminished in properly engineered band structures. >

Electronic structure and properties of Bi2Sr2CaCu2O8, the third high-Tc superconductor

Abstract: Results of a highly precise local density determination of the electronic structure (energy bands, densities of states, Fermi surface and charge densities) of the new high-Tc superconductor Bi2Sr2CaCu2O8 are presented. The calculations employed the full-potential linearized augmented plane wave (FLAPW) method and the subcell structure parameters given by the work of Hazen et al. and Sunshine et al. As in the case of the other Cu-O superconductors, we find a relatively simple band structure at EF and strongly anisotropic highly 2D properties. The Sr and Ca atoms are highly ionic, with the Ca2+ ions serving to insulate the Cu-O planes. The Bi-O planes contribute substantially to N(EF), the density of states at EF, and to the transport properties whereas neither the Sr or Ca do. The N(EF) contribution from the Cu-O planes (∼1.0 states/eV-Cu atom) is lower (per Cu atom) than that found previously for the La-Sr-Cu-O and Y-Ba-Cu-O superconductors. The highly 2D Fermi surface shows regions of strong Cu-O and Bi-O hybridization from which highly anisotropic superconducting energy gaps are predicted. Here, too, an electron-phonon calculation of Tc (using the crude rigid ion approximation) is found to be inadequate. As in the case of YBa2Cu3O7-δ, strongly localized states at EF (arising from Bi-O and Cu-O) may be responsible for charge transfer excitations (excitons) which cause the high Tc.

Extremely wide modulation bandwidth in a low threshold current strained quantum well laser

Abstract: Lasing characteristics of strained quantum well (QW) structures such as InGaAs/AlGaAs on GaAs and InGaAs/InAlAs on InP were analyzed by taking into account the band mixing effect in the valence band. A relaxation oscillation frequency fr, which gives a measure of the upper modulation frequency limit, was found increased three times in a 50 A In0.9Ga0.1As/In0.52Al0.48As QW structure compared with that in a 50 A GaAs/Al0.4Ga0.6As QW structure for the undoped case. One of the main factors for this improved frequency bandwidth is attributed to the reduced subband nonparabolicity as well as the reduced valence‐band density of state in the strained QW structure. The corresponding lasing threshold current is one order of magnitude smaller than that of the GaAs/AlGaAs QW structure. With a p doping in the QW the fr value increases, and the 3 dB cutoff frequency of about 90 GHz will be expected with an acceptor concentration of 5×1018 cm−3 in the In0.9Ga0.1As/In0.52Al0.48As QW.

Effect of bismuth on high-Tc cuprate superconductors: Electronic structure of Bi2Sr

Abstract: The electronic structure of the new Bi-based high-temperature superconductor, with ${T}_{c}$ onsets above 110 K, is shown to be altered considerably from that of the other cuprate superconductors by the presence of Bi. There are Bi-O bands which cross the Fermi level, and the two-dimensional character of the bands is even greater than that of previous cuprates. Like the other cuprates, band critical points occur at the Fermi level.

Heavy-fermion quasiparticles in UPt3.

Abstract: The quasiparticle band structure of the heavy-fermion superconductor ${\mathrm{UPt}}_{3}$ has been investigated by means of angle-resolved measurements of the de Haas\char21{}van Alphen effect. Most of the results are consistent with a model of five quasiparticle bands at the Fermi level corresponding to Fermi surfaces similar to those calculated by band theory. However, as inferred from the extremely high cyclotron masses, the quasiparticle bands are much flatter than the calculated ones. The nature of the observed quasiparticles and their relationship to thermodynamic properties are briefly considered.

Free carrier and many-body effects in absorption spectra of modulation-doped quantum wells

Abstract: The temperature-dependent optical absorption and luminescence spectra of GaAs/AlGaAs and InGaAs/InAlAs n-doped modulation-doped quantum wells is discussed with emphasis on the peak seen at the edge of the absorption spectra of these samples A many-body calculation of the electron-hole correlation enhancement is presented, which identifies this peak with the Mahan exciton-the result of the Coulomb interaction between the photoexcited hole in the valence band and the sea of electrons in the conduction band This calculation accounts for the strong dependence of the absorption edge peak on both the temperature and carrier concentration, in good qualitative agreement with experimental data and with previously published results The changes induced by the carriers on the subband structure through self-consistent calculations are also analyzed, and it is concluded that in these symmetric structures, the changes are small for achievable carrier densities >

The effect of heteroatomic substitutions on the band gap of polyacetylene and polyparaphenylene derivatives

Abstract: The electronic structures of polyparaphenylene (PPP), polyacetylene (PA), and their derivatives with small energy gaps have been studied by the Huckel and MNDO crystal orbital methods. The effect of nuclear relaxation and heteroatomic substitution on the energy gaps (Eg) have been taken into account by compelete geometry optimization using periodic boundary conditions as opposed to earlier cluster based calculations. Calculations were done on the following polyacetylene derivatives: polypyrrole (PPy), polythiophene (PT), polyisothianaphthene (PITN), poly (5,5’‐bithiophene methenyl) (PBTM, 11, X=S, R=H, m1=m2=1), and poly (5,5’‐bipyrrole methenyl) (PBPM, 11, X=NH, R=H, m1=m2=1). Energetics and band gaps for the two isomeric forms, the quinoid and aromatic structures of PPy and PT, are discussed and critically compared with previous calculations. Perturbational molecular orbital theory is invoked to explain the narrower Eg for PITN, PBTM, and PBPM, relative to that of PA. Calculations for PPP derivatives {m...

Band structure of carbonated amorphous silicon studied by optical, photoelectron, and x-ray spectroscopy

Abstract: Hydrogenated silicon-carbon films prepared by glow discharge from silane-methane mixtures at low power density are used as a model system for the analysis of optical properties and band structure of amorphous tetrahedral semiconductors. Between 0 and 20 at. % of carbon in the solid, the optical gap and the static refractive index can be varied over a wide range without changing the chemical structure of the solid and its good semiconducting properties. The optical constants are well described by a simple two-band model of optical transitions, and the information on the band structure in the solid is condensed into one parameter, the average gap ${E}_{M}$, which corresponds to the energy difference between the centers of gravity of the valence and conduction bands. This value is very close to the energy spacing of the maxima in the distributions of the conduction and valence band deduced from soft-x-ray spectra, and exhibits a similar increase with carbon content. Beyond a carbon concentration of about 20 at. %, we observe a change in the nature of the material. The average gap ${E}_{M}$ increases much more rapidly than the optical gap; x-ray photoelectron spectroscopy indicates an incorporation of carbon in the form of Si-C-Si units in a tetrahedral network, whereas for concentrations smaller than 20 at. % the carbon is mainly incorporated as methyl groups ${\mathrm{CH}}_{3}$.

Chain-fragment doping and the phase-diagram of yba2cu3o7-x

Abstract: We show, using a proposed oxygen-defect structure for ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}$ and a tight-binding model based on density-functional calculations, that the distribution of holes between planes and (fragmented) chains causes jumps and plateaus for the hole counts in the planes as a function of the nonstoichiometry, $x$. These features can be correlated with the occurrence of the antiferromagnetic as well as the 60- and 90-K superconducting phases. Our findings are supportive of the view that the hole count is the controlling parameter for the superconductivity.

Spin-dependent photoabsorption at theL-edges of ferromagnetic Gd and Tb metal

Abstract: The spin-dependent absorption of circularly polarized x-rays is studied at theL-edges of ferromagnetic Gd and Tb metal. At theL1-edge a spin-dependent part of the absorption coefficient of 10−3–10−2 is observed. Strong resonance absorption known as “white line” occurs at theL2- andL3-absorption onset. Correlated with it one finds large spin-dependent absorption effects with amplitudes of a few percent. The spin-dependent absorption spectra reflect the profiles of the spin densities of the states populated in the absorption process. Thep-states show spin densities correlated with the first two flat bands above the Fermi level. The spin density of thed-like states is concentrated in the energy range of the white line. In Gd a splitting of ∼(0.5–0.6) eV of the unoccupied 5d spin up and spin down bands is indicated for both spin-orbit partners. In Tb a large dependence of the 5d spin density on the spin-orbit configuration is observed. The experimental results on the spin densities in Gd are compared with band structure calculations for the ferromagnetic ground-state. The theoretical and experimental spin density profiles agree well for thep-states but not for thed-states. The discrepancy concerning thed-states may be attributed to core-hole polarization effects in the absorption process.

Analysis of electronic structure and charge density of the high-temperature superconductor YBa2Cu3O7

Abstract: Self-consistent linearized augmented plane wave (LAPW) method calculations of the band structure, density of states, Fermi surface, Coulomb potential, charge density, core-level shifts, and electron-phonon interaction are presented for Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/. The calculated Sommerfield parameter ..gamma.. is 4.35 mJ(mole Cu)/sup /minus/1/ K/sup /minus/2/, roughly about a factor of 2 smaller than experimentally deduced values of the enhanced value ..gamma.. = (1 + lambda)..gamma../sub 0/, suggesting that the Fermi surface mass enhancement is of the order of unity. The crystal charge density is best represented by overlapping spherical ionic densities when the Cu and O ions are assigned charges of +1.62 and -1.69, respectively, corresponding to about 0.3 holes per oxygen atom. Core-level energies for the inequivalent atoms differ by as much as 0.45 eV for Cu and 0.7 eV for O, amounts which may be detectable by core-level spectroscopies. These results provide important information on the character and magnitude of ionic contributions to bonding in these materials. Within the rigid muffin-tin approximation, calculated McMillan-Hopfield parameters yield estimates for the electron-phonon strength lambda that appear to be too small to account for the observed T/sub c/. We point out an unusual band of oxygen-derived chain states below, butmore » within 0.1 eV of, the Fermi level.« less

Structural and electronic properties of WC.

Abstract: We present the results of a pseudopotential local-orbital calculation on hexagonal WC. The calculated lattice constants and cohesive energy are in good agreement with experiment, and the calculated bulk modulus lies within the wide range of measured values. The band structure and Fermi surface obtained are also generally consistent with experimental data, and the Fermi level is found to lie in a deep minimum of the density of states. The calculated valence electron charge density indicates that the bonding in WC consists of a metallic component similar to that found in solid W, and strong W-C bonds.

Unoccupied molecular orbitals of aromatic hydrocarbons adsorbed on Ag(111)

Abstract: The unoccupied π* bands of epitaxial overlayers of benzene, naphthalene, anthracene, tetracene, perylene, and coronene on a Ag(111) surface have been studied by angle resolved inverse photoemission spectroscopy. A comparison with HAM/3 MO calculations and electron transmission gas phase measurements enables the assignment of the π* affinity levels of these organic systems. In conjunction with previous angle resolved photoemission, optical absorption, and near edge x‐ray absorption studies a complete picture of their valence band structure and morphology evolves. Optical and x‐ray absorption excitation energies are discussed in the light of the experimentally determined one‐electron correlation diagram. Gas phase–solid relaxation energies of the affinity levels are found to decrease in the series of benzene to tetracene (1.7→0.5 eV) attributed to the increasing size of the involved molecular orbitals. For benzene a low lying σ*‐shape resonance has been identified in the isochromat inverse photoemission spe...

Quasiparticle band structure of Na and simple metals

Abstract: We have made absolute measurement of the quasiparticle band structure of Na(110) using angle-resolved photoemission. These data show that the occupied band is parabolic but with an 18% narrowing in bandwidth compared to self-consistent band calculations. A simple model calculation of the self-energy correction for a homogeneous electron gas produces good agreement with the data, if a dielectric response beyond the random-phase approximation is included. Experiment and theory are compared for other simple metals.

Noise spectroscopy of deep level (DX) centers in GaAs‐AlxGa1−xAs heterostructures

Abstract: We have measured the generation‐recombination noise from the donor‐related DX centers in current biased GaAs/AlxGa1−xAs heterostructures from 1 Hz to 25 kHz and from 77 to 330 K. A significant noise contribution from these traps is observed even at Al mole fractions below 0.2, where the trap level is resonant with the conduction band. The activated behavior of the noise spectrum from this resonant level is very similar to that observed at higher Al mole fractions, when the level lies deep in the fundamental gap. This result can be predicted, based on the recently elucidated relationship of the trap level to the band structure of AlxGa1−xAs. In accordance with other experimental results, the noise spectra demonstrate that the emission and capture kinetics of the level are unperturbed by its resonance with the conduction band. We briefly discuss some implications of these results for heterostructure transistor design.

Mechanisms of Schottky‐barrier formation in metal–semiconductor contacts

Abstract: During the formation of metal–semiconductor contacts two principally different types of electronic states are effective in determining the surface position of the Fermi level within the semiconductor band gap. These are, first, adatom‐related surface states of donor character and, second, the continuum of adsorbate‐induced interface states which result from the tailing of the metal wave functions into the virtual gap states of the semiconductor band structure. The first type of state is observed at submonolayer coverages either after depositions at low temperatures or even at room temperature when a cation exchange occurs. Each metal adatom contributes one of those surface donors and their energy levels are linearly correlated with the first ionization energies of the metal atoms. The second type of state exists at interfaces under metallic islands and continuous metallic films. The charge transferred across the interface by these tails of the metal wave functions is explained by the difference in electro...

Electronic structure of localized Si dangling-bond defects by tunneling spectroscopy.

Abstract: Scanning tunneling microscopy is used to determine the atomic structure, charge state, and electronic energy spectrum of isolated Si dangling-bond defects at the Al/Si(111) surface. Si adatoms substituting for Al in the first atomic layer give rise to a dangling-bond defect state near —0.4 eV which is strongly localized in space. Tunneling spectra and local band-bending measurements are inconsistent with simple one-electron band theory and demonstrate the importance of many-electron effects.

Electronic structure and properties of the high-Tc superconductors: Tl2Ba2CaCu2O8 and Tl2Ba2Ca2Cu3O10

Abstract: We present results of highly precise local density calculations of the electronic structure of the two high- T c superconductors Tl 2 Ba 2 CaCuO 8 ( T c ≅112 K) and Tl 2 Ba 2 Ca 2 Cu 3 O 10 ( T c ≅125 K), as obtained with the full potential linearized augmented plane wave (FLAPW) method. A relatively simple band structure is found near E F and strong 2D properties are predicted. Again as in the case of the other high- T c materials, Ba and Ca are highly ionic, with the Ca 2+ ions insulating the Cu-O planes. The Tl-O complexes, which are decoupled from the Cu-O planes, produce small electron pockets at E F with predominant O character that contribute to the transport properties. Each Cu-O plane is found to contribute ≃ 1 state/(eV-Cu atom) to the density of states (DOS) at E F , similar to the Bi 2 Sr 2 CaCu 2 O 8 case. Remarkable strong fermi surface nesting is found along the (100) and (010) directions for the 2D Cu-O dpσ bands. Significantly, we show that the usual simple nearest-neighbors only tight-binding model cannot properly describe these states. Crude rigid ion calculations show that a purely electron-phonon mechanism is inadequate to explain the observed high T c . As in the case of the other high- T c superconductors, a charge transfer excitation (excitonic) mechanism appears likely. Interestingly, the partial DOS structure shows that both systems can be viewed as a metal-semiconductor (or metal-semimetal) superlattice indicating a possible relation to the Allender, Bray, and Bardeen model of excitonic superconductivity.

Modern Aspects of Solid State Chemistry

Abstract: 1. Lattice Dynamics.- Theory of Small Oscillations.- Effect of Lattice Symmetry.- Density of Vibrational States.- Vibrational Thermodynamic Properties of Crystals.- X-ray and Neutron Scattering.- 2. Cohesive Energies of Ionic Solids.- Born-Haber Cycle.- Born Treatment of Ionic Solids.- Some Related Aspects.- 3. Defect Chemistry and Non-Stoichiometric Compounds.- Point Defect Equilibria in Crystals.- The Systematica of Non-Stoichiometric Compounds.- Grossly Non-Stoichiometric Compounds.- Ferrous Oxide: A Case History.- Strong Defect Ordering: Intermediate Superstructure Phases.- Elimination of Defects: Crystallo graphic Shear.- Imperfections of Ordered Structures (Lattice Imaging).- Conclusions and Outstanding Problems.- 4. Theory of Point Defects in Ionic Crystals.- to Point Defects in Ionic Crystals.- Experimental Studies of Point Defects.- Theoretical Calculations of the Formation Energies of Schottky Defects.- Defect Interaction Energies.- Migration Energies.- Interstitial Defects.- Concluding Remarks.- 5. Dielectric Properties.- Definitions and Units.- Mechanisms of Polarization.- Alternating Current Phenomena.- Ferroelectrics.- 6. Magnetism.- Non-Interacting Atoms.- Magnetic Interactions.- Long-Range Order.- Spiral Configurations.- Magnetic Atoms in a Crystal.- Superexchange Interactions.- Collective d-Electron Model.- 7. Neutron Diffraction and Solid State Properties.- Thermal Neutrons.- Elastic Scattering.- Inelastic Scattering.- Conclusions.- 8. Magnetic Resonance.- Nuclear Moments end Nuclear Magnetic Resonance.- Spin-Lattice Relaxation.- Bloch Equations and Transverse Relaxation.- Experimental Arrangements.- NMR in Non-metallic Solids.- Quadrupolar Splittings in NMR.- NMR in Metals.- Chemical Shift and Spin Coupling in Solids.- Pure Quadrupole Resonance in Solids.- Electron Paramagnetic Resonance.- Concluding Remarks.- 9. Nuclear Magnetic Resonance in Superconductors and Dilute Alloys.- NMR in Superconductors.- NMR in Dilute Alloys.- 10. Magnetostriction in Materials.- Behaviour of Common Materials.- Conclusions.- 11. Mossbauer Effect and Dynamics of Atomic Motion in Solids.- Resonance Fluorescence.- Mossbauer's Experiment.- Resonance Absorption of Gamma Rays and Dynamics of Atomic Motion.- Experimental Results.- Concluding Remarks.- 12. Positron Annihilation in Solids.- Methods and Results.- 13. Elements of Order-Disorder Theory and Diverse Applications.- Statement of the Problem.- The Zero Order Approximation (Langmuir Isotherm).- The Fermi-Dirac Distribution Function.- Decomposition of the Lattice into Subfigures.- The Fowler-Guggenheim Adsorption Isotherm.- Thermodynamic Properties of Binary Mixtures in the Bragg-Williams Approximation.- 14. Diffusion in Solids.- The Diffusion Coefficient.- Intrinsic Diffusion Coefficients.- Self-Diffusion Coefficients.- Experimental Procedures.- 15. Ionic Conductivity.- Conduction Mechanisms in Ionic Crystals.- Anisotropy of Conduction in Ionic Crystals.- 16. Inorganic Glasses.- Constitution of Glass.- Glass formation.- Inorganic Glass Forming Systems.- Transport Properties of Glasses.- 17. Electrical Properties of Solid Catalysts.- Historical Introduction.- Classification of Solid Catalysts based on Electronic Properties.- Inverse Mixed Catalysts.- Conclusions.- 18. Dislocations and Solid State Reactions.- Dislocations, Their Structure and Properties.- The Role of Dislocations in Chemical Reactions.- 19. Solid State Reactions.- Role of Defects in the Reactivity of Solids.- Solid-Gas Reactions: Oxidation of Metals.- Solid-Solid Reactions.- Thermal Decomposition of Solids.- 20. Band and Transport Theories in Solids.- to Band Structure Concepts (Particle-in-the-Box).- Kronig-Penney Model.- Bloch Functions for the Circular Chain.- Band Structure for a Circular Chain in the Tight Binding Approximation.- Pauli Exclusion Principle and Fermi-Dirac Statistics.- Heat Capacity of a Metal.- Classification of Materials.- Elementary Discussion of Yarious Transport Phenomena.- Fermi Levels and Conductivity in Intrinsic and Extrinsic Semiconductors.- Transport Effects in Materials Characterized by 'Hopping' Electrons.- Brief Survey of Experimental Results.- 21. Spectroscopy of Metals and Semiconductors.- Macroscopic Theory and Experimental Methods.- Microscopic Theory of Optical Properties.- Optical Properties of Metals.- Optical Properties of Semiconductors.- Conclusions.- 22. Phase Transformations in Solids.- Thermodynamic Considerations.- Structural Changes in Transformations.- Kinetics of Transformations.- Order-Disorder Transitions.- Martensite Transformations.- Ferroelectric Transformations.- Magnetic Transitions.- Semiconductor-Metal Transitions.- High Pressure Transformations.- Born Treatment of Phase Transformations in Alkali Halides.- Comments on Experimental Techniques.

PbTe/Pb/sub 1-x/Sn/sub x/Te (x<or=0.18) multiquantum wells: magnetooptics, four-wave mixing, and band structure

Abstract: Theoretical and experimental investigations on a narrow-gap multiquantum well (MQW) system with a many-valley band structure: PbTe/PbSnTe are presented. This system has a number of interesting features, including weak confinement of electrons and strain splitting of equivalent L-states, comparable to the conduction-band discontinuities. The result of empirical tight-binding calculations, namely, a type I band alignment, is confirmed by magnetooptical investigations in both magnetic-field orientations parallel and perpendicular to the layers. An envelope function calculation including quantizing magnetic fields is used for the analysis. >

The fermi surface in YBa2Cu3O7−x BY 2D ACAR

Abstract: Positron-annihilation two-dimensional angular correlation measurements (2D ACAR) have been performed on a YBa2Cu3O7−x single crystal with Tc = 93.6 K. Projections both parallel and perpendicular to the c-axis were obtained. On the basis of these experiments, we propose that the Fermi surface consists of four nearly cylindrical sheets, in substantial accord with band theory predictions. These are first Fermi surfaces measured directly via c-axis projection in a high-Tc superconductor.

Electronic structure of MnO studied by angle-resolved and resonant photoemission

Abstract: Results are reported from angle-integrated, angle-resolved, and resonant photoemission measurements on cleaved MnO single crystals using synchrotron radiation. Normal-emission spectra from a cleaved (100) surface indicate that the relative dispersion of Mn 3d states in the valence band is less than \ifmmode\pm\else\textpm\fi{}0.1 eV along \ensuremath{\Gamma}--\ensuremath{\Delta}--X in the Brillouin zone, which supports the view of highly localized 3d electrons on the ${\mathrm{Mn}}^{2+}$ cations. The results of polarization-dependent and off-normal-emission measurements are also consistent with a localized Mn 3d orbital picture. To explain the presence of satellite photoemission peaks, a hybridization between Mn 3d and O 2p valence states must be invoked. The degree of hybridization is evident from resonant-photoemission measurements at the Mn 3p\ensuremath{\rightarrow}3d absorption threshold. The antiresonant behavior of the 3d-derived states near the top of the valence band in constant-initial-state spectra suggests that MnO is a charge transfer rather than a Mott insulator. The experimental results are discussed in the context of recent cluster and band theories which have been proposed to explain the insulating nature and electronic structure of MnO.