276 results on '"L. M. Falicov"'
Search Results
2. Electron scattering at interfaces: A tight-binding approach
- Author
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L. M. Falicov and Leonor Chico
- Subjects
Materials science ,Reflection (mathematics) ,Tight binding ,Magnetoresistance ,Condensed matter physics ,Scattering ,Superlattice ,Giant magnetoresistance ,Electronic structure ,Reflection coefficient - Abstract
We examine, within the tight-binding approximation, the transmission and reflection coefficients at a bimetallic interface as a function of the interface atomic structure. This is a crucial issue in the study of electronic transport in multilayered systems in general, and the so-called giant magnetoresistance in magnetic multilayers in particular. We have investigated the effect of an additional thin layer of a different material at the interface (analogous to delta doping in semiconductors). We find that, depending on the electronic structure of the materials, the reflection coefficient may be either enhanced or suppressed, and that the presence of interface electronic states causes dramatic increases in the reflection coefficient.
- Published
- 1995
- Full Text
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3. Many-body calculation of the magnetic, optical, and charge-transfer spectra of solid oxygen in the α and β phases
- Author
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Antônio J. R. da Silva and L. M. Falicov
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Physics ,Solid oxygen ,Charge (physics) ,Electron ,Atomic physics ,Ground state ,Spin (physics) ,Energy (signal processing) ,Spectral line ,Basis set - Abstract
The electronic spectra of \ensuremath{\alpha} and \ensuremath{\beta} solid ${\mathrm{O}}_{2}$ were calculated in a full many-body approach for a cluster consisting of four ${\mathrm{O}}_{2}$ molecules with periodic-boundary conditions. By including only the partially occupied \ensuremath{\pi} orbitals (16 spin orbitals, 8 electrons) the basis set consists of 12 870 many-electron states. The resulting spectra contains three basic types of excitations at very different energy ranges: (a) 81 states corresponding to the ground state and magnetic excitations (magnons) within 100 meV; (b) 1215 states of neutral molecular excitations (excitons) with energies from about 1 to 8 eV; and (c) 11 574 charge-transfer states with excitation energies up to 60 eV. Analysis of the properties of the ground states in both \ensuremath{\alpha} and \ensuremath{\beta} solid ${\mathrm{O}}_{2}$ has been carried out. The lowest many-body states, those that correspond to neutral, unexcited molecules, describe accurately the magnetic excitations of both solids. The two phases have very different spectra resulting, even at very low temperatures, in a sizeable difference in the (magnetic) entropy. The calculated entropy difference at the observed \ensuremath{\alpha}-\ensuremath{\beta} phase transition temperature agrees surprisingly well with the experimentally measured heat of transformation.
- Published
- 1995
- Full Text
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4. Theory of the negative magnetoresistance of ferromagnetic‐normal metallic multilayers (invited)
- Author
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Randolph Q. Hood and L. M. Falicov
- Subjects
Magnetization ,Materials science ,Condensed matter physics ,Magnetoresistance ,Solid-state physics ,Ferromagnetism ,Scattering ,Relaxation (NMR) ,General Physics and Astronomy ,Electron ,Magnetic field - Abstract
Transport properties for a system consisting of a ferromagnetic‐normal metallic multilayer are theoretically examined. The in‐plane conductance of the film is calculated for two configurations; the ferromagnetic layers aligned (i) parallel and (ii) antiparallel to each other. The results explain the giant negative magnetoresistance encountered in these systems when an initial antiparallel arrangement is changed into a parallel configuration by application of an external magnetic field. The calculation depends on (a) geometric parameters (the thicknesses of the layers); (b) intrinsic metal parameters (number of conduction electrons, magnetization and effective masses in the layers); (c) bulk sample properties (conductivity relaxation times); and (d) interface scattering properties (diffuse scattering versus potential scattering at the interfaces). It is found that a large negative magnetoresistance requires, in general, considerable asymmetry in the interface scattering for the two spin orientations. All qualitative features of the experiments are reproduced. Quantitative agreement can be achieved with sensible values of the parameters. The effect can be conceptually explained based on considerations of phase‐space availability for an electron of a given spin orientation as it travels through the multilayer sample in the various configurations.
- Published
- 1994
- Full Text
- View/download PDF
5. Orientational disorder and the band gap of solid molecular hydrogen under pressure
- Author
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Belita Koiller, Helio Chacham, and L. M. Falicov
- Subjects
Phase transition ,Molecular solid ,Materials science ,Condensed matter physics ,Hydrogen ,chemistry ,Band gap ,Solid hydrogen ,Periodic boundary conditions ,chemistry.chemical_element ,Electronic structure ,Dielectric - Abstract
The influence of librational motion (orientational disorder) on the electronic structure of molecular solid hydrogen is investigated by means of a microcrystal formalism. A cluster consisting of 64 molecules in the hexagonal close-packed structure with periodic boundary conditions is diagonalized exactly in a parametrized tight-binding approximation. The influence of pressure and libration are examined for a variety of orientational structures. It is found that the stable orientational structure varies with pressure, and that orientational phase transitions occur just before the insulator-to-metal transition (closing of the gap). The theoretical results seem to explain satisfactorily the anomalies observed in dielectric measurements of solid hydrogen at high pressure.
- Published
- 1994
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6. Magnetism and the αβ phase transition in solid oxygen
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L. M. Falicov and Antônio J. R. da Silva
- Subjects
Phase transition ,Atomic orbital ,Condensed matter physics ,Spin wave ,Chemistry ,Magnetism ,Solid oxygen ,General Physics and Astronomy ,Electronic structure ,Electron ,Physical and Theoretical Chemistry ,Molecular physics ,Spectral line - Abstract
The electronic condition of α and β solid O2 were calculated in a full many-body approach for a cluster consisting of four O2 molecules with periodic boundary conditions. Only the partially occupied π orbitals (sixteen spin-orbitals, eight electrons) were included. The lowest 81 many-body states, which correspond to neutral, unexcited molecules, describe accurately the magnetic excitations of the solids. The two phases have very different spectra resulting, even at very low temperatures, in a large difference in the (magnetic) entropy. The calculated entropy difference at 23.9 K (the αβ phase transition temperature) agrees surprisingly well with the experimentally measured heat of transfomation.
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- 1994
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7. Effects of interfacial roughness on the magnetoresistance of magnetic metallic multilayers
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L. M. Falicov, Randolph Q. Hood, and David R. Penn
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Condensed Matter::Materials Science ,Materials science ,Magnetoresistance ,Condensed matter physics ,Scattering ,Electrical resistivity and conductivity ,Superlattice ,Condensed Matter::Strongly Correlated Electrons ,Electron ,Surface finish ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Thermal conduction ,Boltzmann equation - Abstract
The Boltzmann equation is solved for a system consisting of a ferromagnetic--normal-metallic multilayer. The in-plane magnetoresistance of Fe/Cr and Fe/Cu superlattices is calculated for (1) varying interfacial geometric random roughness with no lateral coherence, (2) correlated (quasiperiodic) roughness, and (3) varying chemical composition of the interfaces. The interplay between these three aspects of the interfaces may enhance or suppress the magnetoresistance, depending on whether it increases or decreases the asymmetry in the spin-dependent scattering of the conduction electrons. Properties of the interfaces relevant to the giant negative magnetoresistance are discussed.
- Published
- 1994
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8. Modulation of the crystal structure in quasi-one-dimensional solids induced by impurities: An atomic-force microscope study
- Author
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Zhenxi Dai, Q. Xue, L. M. Falicov, C. G. Slough, Y. Gong, and R. V. Coleman
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Wavelength ,Amplitude ,Materials science ,Microscope ,Condensed matter physics ,Impurity ,law ,Electric susceptibility ,Microscopy ,General Physics and Astronomy ,Crystal structure ,Microstructure ,law.invention - Abstract
An atomic-force microscope study of interstitial impurities in the quasi-one-dimensional charge-density-wave system NbSe[sub 3] at room temperature (in the normal phase) exhibits long-range periodic lattice modulations. The amplitudes and wavelengths are strong functions of the impurity concentration, and in the case of vanadium successive wavelengths of 6[ital b][sub 0], 4[ital b][sub 0], and 3[ital b][sub 0] are observed. The drastic changes in the long-range structure of the system caused by small changes in the impurity concentration are an indication of the complex electric susceptibility of a system on the verge of becoming unstable against charge-density-wave formation.
- Published
- 1993
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9. Spin‐density wave, charge density wave, and polarizabilities of C60 in the Pariser–Parr–Pople model
- Author
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F. Willaime and L. M. Falicov
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Condensed matter physics ,Pariser–Parr–Pople method ,Chemistry ,Hartree–Fock method ,General Physics and Astronomy ,Hyperpolarizability ,Charge density ,Polarizability ,Physics::Atomic and Molecular Clusters ,Spin density wave ,Physics::Atomic Physics ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Atomic physics ,Ground state ,Charge density wave - Abstract
The Pariser–Parr–Pople Hamiltonian is investigated on a single C60 molecule in the Hartree–Fock approximation. The effect of on‐site and two‐site electron–electron interactions on the stability of states other than the normal paramagnetic state is studied. In particular (i) a spin‐density wave state, with a structure similar to that of the classical ground state of the antiferromagnetic Heisenberg Hamiltonian; and (ii) a charge density wave state which occurs for weakly screened two‐site interactions. Linear and nonlinear optical properties are also calculated. With the finite field method and the Mo/ller–Plesset correction in second order, a linear polarizability of 325.5 a.u. and a second hyperpolarizability of 5.87×10−36 esu are found.
- Published
- 1993
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10. Non-perturbative theory of spin-polarized electron-capture spectroscopy in ferromagnetic nickel
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L. M. Falicov and W. Hübner
- Subjects
Physics ,Ferromagnetism ,Spin polarization ,Electronic correlation ,Electron capture ,Atom ,Materials Chemistry ,General Chemistry ,Electron ,Atomic physics ,Condensed Matter Physics ,Spin (physics) ,Ion - Abstract
With the purpose of understanding the interaction of nuclear projectiles with ferromagnetic metallic surfaces, Schrodinger's equation is solved along the classical trajectory for head-on collisions of H + ions with a Ni atom on the femtosecond time scale. Many-body effects are treated exactly within single configurations. Probabilities of (21%) and (0.35%) for one-and two-electron capture and a spin polarization of (−82%) are found, in good agreement with experiment. The predominant capture of minority electrons, caused by angular-momentum conservation, is strongly enhanced by electron correlation. Electron capture probes magnetism as a phenomenon of correlated electrons on a significantly longer time scale than single-electron properties such as charge transfer.
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- 1993
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11. THEORY FOR SPIN–POLARIZED ELECTRON CAPTURE SPECTROSCOPY IN FERROMAGNETIC NICKEL
- Author
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L. M. Falicov and W. Hübner
- Subjects
Physics ,Magnetism ,Scattering ,Electron capture ,Statistical and Nonlinear Physics ,Electron ,Condensed Matter Physics ,Quantum number ,Schrödinger equation ,symbols.namesake ,symbols ,Atomic physics ,Spectroscopy ,Hamiltonian (quantum mechanics) - Abstract
A time-dependent many-body theory is developed for the study of spin-polarized electron capture spectroscopy. As a model system we choose the head-on collision of protons with a nickel atom. For the electronic part of the Hamiltonian we use the most general on-site interaction terms allowed by atomic symmetry. The total electronic many-body states are group-theoretically classified with respect to the conserved quantum numbers L, L z and S z. The time-dependent Schrödinger equation for this system is solved exactly. The zero-, one- and two- electron capture probabilities which are treated on the same footing are monitored along the trajectories of the scattering species on the femtosecond time scale. In good agreement with experiments on surfaces we find probabilities of 22% and 0.33% for one- and two-electron capture respectively and spin polarizations between -60% and -100%. The predominant capture of minority electrons is enhanced due to electronic correlations. This implies that the probing of magnetism occurs on a significantly longer time scale than the probing of single electron properties.
- Published
- 1993
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12. ChemInform Abstract: Surface, Interface and Thin-Film Magnetism: An Overview
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L. M. Falicov
- Subjects
Surface (mathematics) ,Field (physics) ,Chemistry ,Magnetism ,Interface (Java) ,Measure (physics) ,General Medicine ,Thin film ,Engineering physics ,Characterization (materials science) - Abstract
A general view is presented of the state of the art in the field of surface, interface and thin film magnetism. The following items are discussed: (1) new growth techniques which produce atomically engineered novel materials; (2) characterization techniques to measure magnetic properties of these systems; and (3) computational advances which allow large complex calculations. Issues of fundamental and technological interest for possible future research are highlighted.
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- 2010
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13. Metallic Magnetic Superlattices
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L. M. Falicov
- Subjects
Materials science ,Information storage ,Magnet ,Superlattice ,Pillar ,General Physics and Astronomy ,Nanotechnology ,Material system - Abstract
Artificially made, ordered material systems are a pillar of late‐20th‐century advanced technology. In principle, metallic magnetic superlattices—also called magnetic multilayers—should exhibit more new and interesting physical effects than any other artificially made material system. This gives them the potential for many technological advances in information storage and retrieval and in the synthesis of new magnets for a variety of applications.
- Published
- 1992
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14. Boltzmann-equation approach to the negative magnetoresistance of ferromagnetic–normal-metal multilayers
- Author
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Randolph Q. Hood and L. M. Falicov
- Subjects
Condensed Matter::Materials Science ,Magnetization ,Materials science ,Effective mass (solid-state physics) ,Condensed matter physics ,Magnetoresistance ,Phonon scattering ,Scattering ,Superlattice ,Diffuse reflection ,Boltzmann equation - Abstract
The Boltzmann equation is solved for a system consisting of a ferromagnetic--normal-metal--ferromagnetic metallic trilayer. The in-plane conductance of the film is calculated for two configurations: the ferromagnetic layers aligned (i) parallel and (ii) antiparallel to each other. The results explain the giant negative magnetoresistance encountered in these systems when an initial antiparallel arrangement is changed into a parallel configuration by application of an external magnetic field. The calculation depends on (a) geometric parameters (the thicknesses of the layers), (b) intrinsic metal parameters (number of conduction electrons, magnetization, and effective masses in the layers), (c) bulk sample properties (conductivity relaxation times), (d) interface scattering properties (diffuse scattering versus potential scattering at the interfaces), and (e) outer surface scattering properties (specular versus diffuse surface scattering). For perfect specular scattering at the surfaces the problem becomes identical to an infinite multilayer, periodic system. It is found that a large negative magnetoresistance requires, in general, considerable asymmetry in the interface scattering for the two spin orientations. All qualitative features of the experiments are reproduced. Quantitative agreement can be achieved with sensible values of the parameters. The effect can be conceptually explained based on considerations of phase-space availability for an electron of a given spinmore » orientation as it travels through the multilayer sample in the various configurations.« less
- Published
- 1992
- Full Text
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15. Surface, interface and thin film magnetism: an overview
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L. M. Falicov
- Subjects
Surface (mathematics) ,Materials science ,Field (physics) ,Magnetism ,Interface (Java) ,Superlattice ,Metals and Alloys ,Measure (physics) ,Mineralogy ,Surfaces and Interfaces ,Engineering physics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Characterization (materials science) ,Materials Chemistry ,Thin film - Abstract
A general view is presented of the state of the art in the field of surface, interface and thin film magnetism. The following items are discussed: (1) new growth techniques which produce atomically engineered novel materials; (2) characterization techniques to measure magnetic properties of these systems; and (3) computational advances which allow large complex calculations. Issues of fundamental and technological interest for possible future research are highlighted.
- Published
- 1992
- Full Text
- View/download PDF
16. Heavy-fermion systems in magnetic fields: The metamagnetic transition
- Author
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L. M. Falicov and James Freericks
- Subjects
Physics ,Magnetization ,Condensed matter physics ,Magnetism ,Superexchange ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,Fermion ,Ground state ,Metamagnetism ,Magnetic field - Abstract
Heavy fermions have a large number of low-lying excitations. Antiferromagnetic superexchange typically favors low-spin arrangements for the ground state. A magnetic field favors high-spin arrangements over low-spin arrangements. The transition from a low-spin ground state to a high-spin ground state, as a function of magnetic field, passes through a range where there is a peak in the many-body density of states. This range qualitatively describes the metamagnetic transition.
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- 1992
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17. Calculation of optical transitions inNiI2andCoI2under pressure
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L. M. Falicov and Antônio J. R. da Silva
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chemistry.chemical_classification ,chemistry ,Condensed matter physics ,Nickel compounds ,Electronic structure ,Atomic physics ,Ground state ,Inorganic compound ,Néel temperature ,Charged particle ,Spectral line ,Iodine compounds - Abstract
A calculation of the electronic spectra of ${\mathrm{Co}}^{2+}$ in insulating ${\mathrm{CoI}}_{2}$ and ${\mathrm{Ni}}^{2+}$ in insulating ${\mathrm{NiI}}_{2}$ as a function of pressure is presented. The results depend crucially on the variation with pressure of the crystallographic (c/a) and u parameters. Level crossings are expected as a function of increasing pressure, including a possible change in the symmetry of the ground state for ${\mathrm{NiI}}_{2}$.
- Published
- 1992
- Full Text
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18. Phase diagram for sodium clusters
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L. M. Falicov and Amitesh Maiti
- Subjects
Pseudopotential ,Physics ,Condensed matter physics ,chemistry ,Phase (matter) ,Diffusionless transformation ,Sodium ,Jellium ,Thermodynamics ,chemistry.chemical_element ,Melting line ,Atomic and Molecular Physics, and Optics ,Phase diagram - Abstract
A temperature-size (T-N) phase diagram is derived for Na clusters of up to N\ensuremath{\sim}1000 atoms. It is based on first-order pseudopotential calculations and the Lindemann criterion for melting. It contains three regions of stability: (1) a liquid (jellium) phase at temperatures above the melting line ${\mathit{T}}_{\mathit{M}}$(N); (2) a phase related to the body-centered-cubic structure at temperatures below the melting line; and (3) a close-packed structure at very low temperatures and sufficiently large N. The melting line drops to ${\mathit{T}}_{\mathit{M}}$(N)=0 for N65. The phase diagram reduces asymptotically to the known phases of Na as N\ensuremath{\rightarrow}\ensuremath{\infty}, including the known martensitic transformation at T\ensuremath{\approxeq}5 K.
- Published
- 1992
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19. Thermodynamic model of the insulator-metal transition in nickel iodide
- Author
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L. M. Falicov and James Freericks
- Subjects
Condensed Matter::Quantum Gases ,Phase transition ,Materials science ,Condensed matter physics ,chemistry.chemical_element ,Nickel ,Mean field theory ,chemistry ,Superexchange ,Critical point (thermodynamics) ,Condensed Matter::Strongly Correlated Electrons ,Ising model ,Metal–insulator transition ,Phase diagram - Abstract
A model calculation of the phase diagram for the isostructural insulator-metal phase transition of nickel iodide is presented. The system is modeled by the Falicov-Kimball Hamiltonian with the calculated band structure of ${\mathrm{NiI}}_{2}$ and (Ising) spin-spin interactions, but neglects all hybridization effects between nickel 3d and iodine 5p bands. Many-body interactions and spin superexchange are both treated in mean-field theory. The results include second-order antiferromagnetic-paramagnetic insulator transitions, first-order insulator-metal transitions, and a (as yet unobserved and probably unobservable) classical critical point. The calculated phase diagram and transport properties agree well with the recent experimental results.
- Published
- 1992
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20. Quantum tunneling phenomena, John Bardeen, and the tunneling hamiltonian
- Author
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L. M. Falicov
- Subjects
Superconductivity ,Physics ,symbols.namesake ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Quantum mechanics ,symbols ,BCS theory ,Condensed Matter Physics ,Hamiltonian (quantum mechanics) ,Quantum tunnelling ,Electronic, Optical and Magnetic Materials - Published
- 1991
- Full Text
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21. Metastable charge-density-wave states inNbSe3studied by magnetotransport
- Author
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C. G. Slough, L. M. Falicov, R. V. Coleman, Hao-An Lu, and Amitesh Maiti
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Physics ,Condensed matter physics ,Magnetoresistance ,Hall effect ,Electrical resistivity and conductivity ,Condensed Matter::Superconductivity ,Electric field ,Excited state ,Metastability ,Condensed Matter::Strongly Correlated Electrons ,Quantum Hall effect ,Charge density wave - Abstract
Magnetoquantum oscillations in NbSe{sub 3} have been used to study metastable electronic states produced by impurity pinning of charge-density waves (CDW's). Simultaneous measurements of the oscillations in separate sections of the crystal have provided information on the distribution of the metastable domain configurations. A model calculation of the magnetic-breakdown network responsible for the magnetoresistance oscillations was used to generate the various observed frequency distributions. The effects of domain boundaries on the oscillatory components of the magnetoresistance and Hall resistance were evaluated from a simple model. Metastable CDW states are shown to be directly related to the volume impurity pinning of the CDW; they also determine the threshold electric fields required for CDW collective motion.
- Published
- 1991
- Full Text
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22. Hidden symmetries of finite-size clusters with periodic boundary conditions
- Author
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L. M. Falicov and James Freericks
- Subjects
Physics ,Quantum mechanics ,Homogeneous space ,Cluster (physics) ,Periodic boundary conditions ,Hexagonal lattice ,Symmetry group ,Square lattice ,Group theory ,Symmetry number ,Mathematical physics - Abstract
Finite-size clusters with periodic boundary conditions resemble isolated clusters for a small number of sites, and infinite lattices for a large number of sites. The transition from a self-contained system to an infinite lattice passes through an intermediate region with increased (hidden) symmetry. In this high-symmetry region irreducible representations of the space group may stick together to form higher-dimensional representations of the complete symmetry group. This transition is examined for a class of simple-, body-centered-, and face-centered-cubic lattice clusters and the two-dimensional square lattice cluster. The implications of an enlarged symmetry group are also studied for a model of strongly correlated electrons interacting on eight-site clusters.
- Published
- 1991
- Full Text
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23. Enlarged symmetry groups of finite-size clusters with periodic noundary conditions
- Author
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L. M. Falicov and James Freericks
- Subjects
Condensed matter physics ,High Energy Physics::Lattice ,Rotational symmetry ,Statistical and Nonlinear Physics ,Global symmetry ,Symmetry group ,Renormalization group ,Periodic boundary conditions ,Hexagonal lattice ,Gauge theory ,Mathematical Physics ,Mathematics ,Mathematical physics ,Symmetry number - Abstract
Any system that approximates an infinite lattice by a family of finite clusters (with periodic boundary conditions) passes through an intermediate region with enlarged (hidden) symmetry as the system size is increased. The hidden symmetry allows for extra degeneracies and level crossings and has application to exact-diagonalization studies, Monte Carlo simulations, lattice gauge theories, and renormalization group calculations.
- Published
- 1991
- Full Text
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24. Exact solutions of frustrated ordinary and chiral eight-site Hubbard models
- Author
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James Freericks, Daniel S. Rokhsar, and L. M. Falicov
- Subjects
Physics ,Hubbard model ,Heisenberg model ,media_common.quotation_subject ,Frustration ,symbols.namesake ,Tight binding ,Mean field theory ,Quantum mechanics ,t-J model ,symbols ,Condensed Matter::Strongly Correlated Electrons ,Ground state ,Hamiltonian (quantum mechanics) ,media_common - Abstract
This contribution addresses the question of whether or not the ground state of a frustrated spin-1/2 Heisenberg model can be smoothly related to the ground state of a simple tight-binding model at half-filling in an appropriately chosen magnetic field. This continuity is considered explicitly for an eight-site square-lattice Hubbard model with nearest- and next-nearest-neighbor hopping, which approaches a frustrated Heisenberg model with nearest- and next-nearest-neighbor antiferromagnetic exchange coupling in the limit of large Hubbard U. In addition, a counterexample to the widely held belief that the half-filled band of the ordinary Hubbard model is nonmagnetic has been found in the regime where the hopping parameters and Hubbard interaction are all the same order of magnitude.
- Published
- 1991
- Full Text
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25. Electronic and magnetic structure of {111} stacking faults in nickel
- Author
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X.-G. Zhang, L. M. Falicov, Antonios Gonis, J. M. MacLaren, and Daryl C. Chrzan
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geography ,Materials science ,geography.geographical_feature_category ,Spin polarization ,Condensed matter physics ,Magnetic structure ,Stacking ,Electronic structure ,Fault (geology) ,Computer Science::Hardware Architecture ,Density of states ,Electronic band structure ,Computer Science::Operating Systems ,Computer Science::Distributed, Parallel, and Cluster Computing ,Stacking fault - Abstract
The electronic and magnetic structure of {l brace}111{r brace} stacking faults in nickel is investigated utilizing a fully self-consistent, layered multiple-scattering approach which does not require full three-dimensional symmetry or the use of finite-size slabs. The electronic and magnetic structures of a twin boundary, an intrinsic fault, an extrinsic fault, and two other stacking sequences are calculated. In addition, total energies of the faults are calculated and found to be in good agreement with the available experimental results. Localized states appear in all the studied stacking faults; the state's energies and exchange splittings are tabulated. The presence of a stacking fault results in a decrease in the spin polarization near the faults. This decrease arises from subtle changes in the electronic structure arising from the fault. For all the faults, the spin polarization is found to be insensitive to the orientation of the nearest-neighbor atoms, but instead can be related to the distance to the nearest atom in the direction perpendicular to the fault plane. Very simple empirical expressions for calculating the total energy and spin polarization of {ital any} stacking configuration are presented.
- Published
- 1991
- Full Text
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26. Order and disorder in metallic alloys
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Beniamino Ginatempo, H. Rafii-Tabar, V. Kumar, John B. Pendry, H Winter, N. W. Ashcroft, L. M. Falicov, Don M. Nicholson, Julie B. Staunton, Duane D. Johnson, Balazs L. Gyorffy, F. J. Pinski, and G. M. Stocks
- Subjects
Electronegativity ,Physics ,Theoretical physics ,Mean field theory ,State of matter ,Order and disorder ,First principle ,Coherent potential approximation ,Density functional theory ,Local-density approximation - Abstract
Self-consistent ‘band theory’, based on density functional theory, is a useful approach to describing the electron glue which holds solids together. However, its powerful group theoretic and numerical techniques cannot be deployed for disordered states of matter. The self-consistent KKR-CPA is an analogous method which is able to deal with some of these interesting cases. In particular, we show how it describes random metallic alloys, treating all the classic Hume-Rothery factors: size-effect, electronegativity and electrons per atom ratio ( e:a ) on more or less equal footing and from first principles. Moreover, we use the KKR-CPA framework to analyse the instability of the disorder state to compositional ordering processes and hence provide a first principle description of the forces which drive order-disorder transformations.
- Published
- 1991
- Full Text
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27. Gap properties ofAlnGa8−nAs8ordered compounds
- Author
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Roberto Osório, Belita Koiller, and L. M. Falicov
- Subjects
Physics ,chemistry.chemical_classification ,chemistry ,Condensed matter physics ,Band gap ,Oscillator strength ,Cluster (physics) ,Electronic structure ,Composition (combinatorics) ,Electronic band structure ,Inorganic compound ,Energy (signal processing) - Abstract
The small-crystal approach with a 16-site basic cluster is used to determine the electronic structure of 16 inequivalent ordered structures of Al{sub {ital n}}Ga{sub 8{minus}{ital n}}As{sub 8} compounds. The energy gaps and oscillator strengths for the main gap transitions are calculated, and different results are obtained for different structures of the same composition {ital n}, which illustrates the role of compositional ordering in the electronic properties of alloys. Average values of these quantities are used as an attempt to describe Al{sub {ital x}}Ga{sub 1{minus}{ital x}}As alloys. Important features of our results are (a) a positive curvature in the averaged gap versus {ital x} dependence for small {ital x} and (b) a smooth featureless decrease of the averaged oscillator strength with {ital x}. This last feature implies that the direct-indirect gap crossover in the alloy system cannot be genuinely obtained by any sort of averaging among Al{sub {ital n}}Ga{sub 8{minus}{ital n}}As{sub 8} ordered compounds.
- Published
- 1991
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28. Local-chemical-potential approach to small-cluster many-body systems
- Author
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L. M. Falicov and Amitesh Maiti
- Subjects
Physics ,Grand canonical ensemble ,Hubbard model ,Statistical physics ,Many body ,Mathematical physics - Abstract
Etude des moyennes thermodynamiques des occupations locales et des fluctuations d'occupation du nombre local, dans les systemes a plusieurs corps de petits amas en introduisant un potentiel chimique a un site, sur un site particulier. Cette procedure permet l'etude des proprietes differentielles des fonctions thermodynamiques du fait qu'elle fournit une variation continue des occupations locales. Cette methode qui releve de l'ensemble grand canonique de la mecanique quantique, donne un critere pour distinguer les aspects particuliers du petit amas qui survivent dans la limite thermodynamique, de ceux discontinus qui sont caracteristiques de la nature finie du cluster et de l'etat discret du spectre d'energie
- Published
- 1991
- Full Text
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29. Exact many-body solution of the periodic-clustert-t’-Jmodel for cubic systems: Ground-state properties
- Author
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James Freericks and L. M. Falicov
- Subjects
Physics ,Condensed matter physics ,Hubbard model ,Computer Science::Information Retrieval ,t-J model ,Exchange interaction ,Many-body theory ,Periodic boundary conditions ,Parameter space ,Ground state ,Square lattice - Abstract
The {ital t}-{ital t}{prime}-{ital J} model (strongly interacting limit of a particular Hubbard model) is solved exactly on small clusters of eight sites with periodic boundary conditions for the simple-, body-centered-, and face-centered-cubic lattices and for the two-dimensional square lattice. The symmetry, {ital k} vector, and spin of the ground state are studied as functions of crystalline environment, interaction strength, and electron concentration. Phase diagrams are presented for stable solutions, and regions of parameter space that exhibit ferromagnetism and heavy-fermionic behavior are identified.
- Published
- 1990
- Full Text
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30. Surface, interface, and thin-film magnetism
- Author
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S. D. Bader, R. H. Victora, L. M. Falicov, Stuart S. P. Parkin, M. B. Salamon, Ivan K. Schuller, Herbert Hopster, Ronald Gronsky, Daniel T. Pierce, G. A. Prinz, Kristl B. Hathaway, and David N. Lambeth
- Subjects
Surface (mathematics) ,Materials science ,Magnetism ,Interface (Java) ,Mechanical Engineering ,Nanotechnology ,Condensed Matter Physics ,Characterization (materials science) ,Material growth ,Characterization methods ,Mechanics of Materials ,Theoretical methods ,General Materials Science ,Thin film - Abstract
A comprehensive review and state of the art in the field of surface, interface, and thin-film magnetism is presented. New growth techniques which produce atomically engineered novel materials, special characterization techniques to measure magnetic properties of low-dimensional systems, and computational advances which allow large complex calculations have together stimulated the current activity in this field and opened new opportunities for research. The current status and issues in the area of material growth techniques and physical properties, characterization methods, and theoretical methods and ideas are reviewed. A fundamental understanding of surface, interface, and thin-film magnetism is of importance to many applications in magnetics technology, which is also surveyed. Questions of fundamental and technological interest that offer opportunities for exciting future research are identified.
- Published
- 1990
- Full Text
- View/download PDF
31. Fundamentals of the Theory of Metals
- Author
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A. A. Abrikosov and L. M. Falicov
- Subjects
General Physics and Astronomy - Published
- 1990
- Full Text
- View/download PDF
32. Small-crystal approach to ordered semiconductor compounds
- Author
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L. M. Falicov, Maria A. Davidovich, and Belita Koiller
- Subjects
Physics ,Crystallography ,Optics ,business.industry ,Semiconductor materials ,business - Abstract
Calcul des niveaux d'energie electronique de ces composes. La methode fournit le spectre exact d'un hamiltonien de liaison forte pour un amas a 16 sites avec des conditions aux limites periodiques et 5 orbitales par site. Le spectre correspond a la zone fcc de Brillouin a 8 points de symetrie elevee
- Published
- 1990
- Full Text
- View/download PDF
33. Two-state one-dimensional spinless Fermi gas
- Author
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L. M. Falicov and James Freericks
- Subjects
Physics ,Many-body problem ,symbols.namesake ,Fractal ,Quantum electrodynamics ,Numerical analysis ,symbols ,Interaction strength ,Condensed Matter::Strongly Correlated Electrons ,Electronic structure ,Fermi gas ,Hamiltonian (quantum mechanics) ,Phase diagram - Abstract
The two-state, one-dimensional, spinless Fermi gas (Falicov-Kimball model) is studied exactly by numerical calculation and perturbation theory. Rigorous results are presented for small interaction strength and (restricted) coherent and incoherent phase diagrams are calculated for two specific examples. The numerical calculations are extrapolated to provide a qualitative picture of the complete solution. The result includes a fractal structure in which the ground-state changes discontinuously as a function of the parameters.
- Published
- 1990
- Full Text
- View/download PDF
34. Magnetic structure of {111} stacking faults in nickel
- Author
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Xiaoguang Zhang, Daryl C. Chrzan, J. M. MacLaren, Antonios Gonis, and L. M. Falicov
- Subjects
geography ,Materials science ,geography.geographical_feature_category ,Magnetic structure ,Magnetic moment ,Ferromagnetism ,Spin polarization ,Condensed matter physics ,Atom ,Stacking ,General Physics and Astronomy ,Electronic structure ,Fault (geology) - Abstract
The magnetic structure of {111} stacking faults in nickel is investigated utilizing a fully self‐consistent, layered Korringa–Kohn–Rostoker approach which does not require full three‐dimensional symmetry or the use of finite‐sized slabs. Localized electronic states appear at the faults. The spin polarization is calculated for a twin boundary, an intrinsic fault, an extrinsic fault, and several other stacking sequences. In all cases, the magnetic moment is found to be insensitive to the orientation of the nearest‐neighbor atoms, but instead can be related to the distance to the nearest atom in the direction perpendicular to the fault plane. Very simple empirical expressions for calculating the spin polarization and total energy of any stacking configuration are presented.
- Published
- 1990
- Full Text
- View/download PDF
35. Magnetic, Optical and Charge-Transfer Spectra of Antiferromagnetic Solid α-O2 and 'Paramagnetic' Solid β-O2: A Small-Cluster, Many-Electron Calculation
- Author
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L. M. Falicov and Antônio J. R. da Silva
- Subjects
Paramagnetism ,Atomic orbital ,Condensed matter physics ,Chemistry ,Magnon ,Antiferromagnetism ,Electron ,Ground state ,Molecular physics ,Spectral line ,Basis set - Abstract
The electronic spectra of α and β solid O2 were calculated in a full many-body approach for a cluster consisting of four O2 molecules with periodic boundary conditions. By including only the partially occupied π orbitals (16 spin-orbitals, 8 electrons) the basis set consists of 12870 many-electron states. Use of the symmetry properties (group-theoretical analysis) simplifies the problem considerably. Resulting spectra - with phenomenological Hamiltonian parameters obtained from experiment - consist of separate regions: (a) 81 states corresponding to the ground state and low-energy magnetic excitations (magnons); (b) 1215 states of neutral molecular excitations (excitons); and (c) 11574 charge-transfer states (conducting high-energy states). Analysis of the properties of the ground states in both α and β solid O2 has been carried out.
- Published
- 1994
- Full Text
- View/download PDF
36. Theory of spin-polarized electron-capture spectroscopy in ferromagnetic nickel
- Author
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L. M. Falicov and W. Hübner
- Subjects
Elastic scattering ,Physics ,symbols.namesake ,Condensed matter physics ,Spin polarization ,Electron capture ,Scattering ,Many-body theory ,symbols ,Electron ,Atomic physics ,Hamiltonian (quantum mechanics) ,Quantum number - Abstract
A detailed time-dependent many-body theory is developed for the study of spin-polarized electron-capture spectroscopy. The head-on collisions of ${\mathrm{H}}^{+}$, ${\mathrm{D}}^{+}$, and ${\mathrm{He}}^{++}$ ions with a nickel atom are chosen as models. Ionic trajectories are calculated classically taking fully into account the distance-dependent repulsive potential of the nickel 3d electrons. For the electronic part of the Hamiltonian the most general on-site interaction terms allowed by atomic symmetry are used. The total electronic many-body states are classified by group-theoretical methods with respect to the orbital and spin ``good'' quantum numbers, L, ${\mathit{L}}_{\mathit{z}}$, and ${\mathit{S}}_{\mathit{z}}$; the latter two are conserved during the collision process. The nickel configurations 3${\mathit{d}}^{9}$, 3${\mathit{d}}^{8}$, and 3${\mathit{d}}^{7}$ are taken into account. They correspond to the treatment of elastic scattering, one-electron capture, and two-electron capture on the same footing. The time-dependent Schr\"odinger equation for this system is solved exactly. Experimentally accessible quantities such as the occupation numbers of all the states as well as the zero-, one-, and two-electron-capture probabilities are monitored along the trajectories of the scattering species on the femtosecond time scale. Probabilities of 21% and 0.35% for one- and two-electron capture, respectively are found, in good agreement with experiments on surfaces. Similarly, a spin polarization between -60% and -100% is calculated. It turns out that this predominant capture of minority electrons is a consequence of angular-momentum conservation and is strongly enhanced by electron correlations. The result implies that the probing of magnetism by electron capture occurs on a significantly longer time scale than the probing of single-electron properties.
- Published
- 1993
37. Open fermionic quantum systems
- Author
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Emilio Artacho and L. M. Falicov
- Subjects
Physics ,symbols.namesake ,Tight binding ,Condensed matter physics ,Electronic correlation ,Quantum mechanics ,Exchange interaction ,symbols ,Quantum system ,Hamiltonian (quantum mechanics) ,Fermi gas ,Anderson impurity model ,Magnetic impurity - Abstract
A method to treat a quantum system in interaction with a fermionic reservoir is presented. Its most important feature is that the dynamics of the exchange of particles between the system and the reservoir is explicitly included via an effective interaction term in the Hamiltonian. This feature gives rise to fluctuations in the total number of particles in the system. The system is to be considered in its full structure, whereas the reservoir is described only in an effective way, as a source of particles characterized by a small set of parameters. Possible applications include surfaces, molecular clusters, and defects in solids, in particular in highly correlated electronic materials. Four examples are presented: a tight-binding model for an adsorbate on the surface of a one-dimensional lattice, the Anderson model of a magnetic impurity in a metal, a two-orbital impurity with interorbital hybridization (intermediate-valence center), and a two-orbital impurity with interorbital repulsive interactions.
- Published
- 1993
38. Electronic Structure of Highly Correlated Systems
- Author
-
James Freericks and L. M. Falicov
- Subjects
Condensed Matter::Quantum Gases ,Physics ,Valence (chemistry) ,Exact solutions in general relativity ,Magnetism ,Quantum mechanics ,Condensed Matter::Strongly Correlated Electrons ,Electronic structure ,Electron ,Kondo effect ,Fermion ,Anderson impurity model - Abstract
Three different but related problems are discussed in this contribution, all related to the so-called Anderson, Hubbard, and t-J Hamiltonians — the prototype Hamiltonians for systems with highly correlated electrons: (1) The relationship — based on the well known canonical (Schrieffer-Wolff) transformation — between the Anderson model (in the small-hybridization and large-Coulomb-interaction regime) and the local moment, the Kondo, the Hubbard and the t-J models, in particular the phenomena of rare-earth magnetism, intermediate valence, and heavy fermions; (2) The exact solution of these Hamiltonians in the periodic small-cluster approximation and the conditions for the existence of the heavy-fermion phenomenon; (3) The metamagnetic transition in heavy-fermion systems.
- Published
- 1993
- Full Text
- View/download PDF
39. Theory of the Negative Magnetoresistance in Magnetic Metallic Multilayers
- Author
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Randolph Q. Hood and L. M. Falicov
- Subjects
Magnetization ,Materials science ,Magnetoresistance ,Condensed matter physics ,Ferromagnetism ,Scattering ,Electron ,Thermal conduction ,Boltzmann equation ,Magnetic field - Abstract
The Boltzmann equation is solved for a system consisting of alternating ferromagnetic -normal metallic layers. The in-plane conductance of the film is calculated for two configurations: successive ferromagnetic layers aligned (i) parallel and (ii) antiparallel to each other. The results explain the giant negative magnetoresistance encountered in these systems when an initial antiparallel arrangement is changed into a parallel configuration by application of an external magnetic field. The calculation depends on (A) geometric parameters (the thicknesses of the layers); (B) intrinsic metal parameters (number of conduction electrons, Magnetization and effective masses in the layers); (C) bulk sample properties (conductivity relaxation times); and (D) interface scattering properties (diffuse scattering versus potential scattering at the interfaces). It is found that a large negative magnetoresistance requires, in general, considerable asymmetry in the interface scattering for the two spin orientations. All qualitative features of the experiments are reproduced. Quantitative agreement can be achieved with sensible values of the parameters. The effect can be conceptually explained based on considerations of phase-space availability for an electron of a given spin orientation as it travels through the multilayer sample in the various configurations and traverses the interfaces.
- Published
- 1993
- Full Text
- View/download PDF
40. Theory of pressure-induced magnetic and metal-insulator transitions
- Author
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Andreas Giesekus and L. M. Falicov
- Subjects
Physics ,Magnetization ,Condensed matter physics ,Ferromagnetism ,Magnetism ,Hydrostatic pressure ,Condensed Matter::Strongly Correlated Electrons ,Electron ,Symmetry breaking ,Metal–insulator transition ,Phase diagram - Abstract
A theory of pressure-induced simultaneous metal-insulator and magnetic phase transitions is presented. It is based on a model consisting of a periodic lattice with (1) an itinerant-electron band, (2) a narrow dispersionless band (localized states), (3) a hybridization term, (4) a very strong short-ranged repulsion between electrons of opposite spin in the localized states, and (5) a moderately strong short-ranged repulsion between electrons in the itinerant and localized bands. The problem is treated in the Hartree-Fock approximation, allowing spontaneous ferromagnetic broken symmetry. Pressure, which mainly changes the energy separation between the two bands, induces transitions from insulating, (ferro)magnetic states, to metallic states with no localized moments. The transition may be continuous or discontinuous, depending on the values of the interaction parameters. A richly structured phase diagram is obtained. For some values of the parameters the model reproduces in a reasonable fashion and for T\ensuremath{\rightarrow}0 the complex transition recently found in ${\mathrm{NiI}}_{2}$ at pressures of about 19 GPa.
- Published
- 1991
41. Itinerant-electron, one-dimensional magnetic superlattices
- Author
-
L. M. Falicov and Randolph Q. Hood
- Subjects
Physics ,Magnetization ,Paramagnetism ,Ferromagnetism ,Condensed matter physics ,Magnetic moment ,Magnetism ,media_common.quotation_subject ,Antiferromagnetism ,Frustration ,Condensed Matter::Strongly Correlated Electrons ,media_common ,Magnetic field - Abstract
Self-consistent Hartree-Fock calculations are presented for a variety of heterogeneous systems consisting of one-dimensional arrays of itinerant paramagnets, ferromagnets, and antiferromagnets. Several aspects of the multilayers and interfaces are explored: enhancement and reduction of the local magnetic moments, magnetic coupling at the interfaces, magnetic arrangements within each film and among nonneighboring films, the global symmetry of the systems, frustration, orientation of the various moments with respect to an outside applied field, and magnetic-field-induced transitions. The various situations exhibit a rich structure and a wealth of possible magnetic effects.
- Published
- 1991
42. Pseudopotential calculation of the total energy of small sodium clusters: Crossover from electronic closed shells to geometrical-structure stability
- Author
-
L. M. Falicov and Amitesh Maiti
- Subjects
Pseudopotential ,Physics ,chemistry ,Sodium ,Crossover ,Structure (category theory) ,chemistry.chemical_element ,Atomic physics ,Total energy ,Stability (probability) ,Atomic and Molecular Physics, and Optics - Published
- 1991
43. Quasi-parity-conserving octahedral model for (H,Be) and (D,Be) tunneling complexes in silicon
- Author
-
L. M. Falicov and Emilio Artacho
- Subjects
Physics ,Crystallography ,Semiconductor materials ,Matrix element - Abstract
Presentation d'un modele de l'effet tunnel a six sites (octaedrique) pour les complexes accepteurs (H, Be) et (D, Be) dans le silicium. La parite se trouve etre une grandeur conservee, dans l'approximation utilisee pour decrire ces systemes. Avec la conservation de la parite, ce modele donne des spectres qui s'ajustent aux resultats experimentaux avec une precision similaire au modele a quatre sites (tetraedrique) propose anterieurement, mais qui ne presente pas les disparites inexpliquees ― presentes dans le modele tetraedrique ― entre les frequences d'effet tunnel de ces complexes et les frequences rotationnelles des molecules diatomiques correspondantes
- Published
- 1991
44. Surface, Interface and Thin-Film Magnetism: An Overview
- Author
-
L. M. Falicov
- Subjects
Surface (mathematics) ,Materials science ,Field (physics) ,Interface (Java) ,Magnetism ,Thin film ,Engineering physics - Abstract
A brief review of the state of the art in the field of surface, interface and thin-film magnetism is presented.
- Published
- 1991
- Full Text
- View/download PDF
45. Superconducting vortex-line configurations in materials with twin boundaries
- Author
-
Henrik Svensmark and L. M. Falicov
- Subjects
Physics ,Superconductivity ,Condensed matter physics ,Condensed Matter::Superconductivity ,Tourbillon ,Crystal twinning ,Anisotropy ,Type-II superconductor ,Magnetic flux ,Vortex ,Magnetic field - Abstract
We have studied numerically the classical states of equilibrium, stable and metastable, of magnetic-field vortex lines in a type-II superconductor in the presence of twin boundaries which attract the vortex lines. Depending on the value of the magnetic field and the density of the twin boundaries, a variety of situations is found. Among them are Abrikosov lattices, anisotropic structures in which the vortex lines are mostly localized at the twin boundaries, and a consistently large regime of disordered structures. Statistical analyses of the distributions, their energies, and their pair-correlation functions are presented.
- Published
- 1990
46. Ground-state configuration of double acceptors in silicon and germanium
- Author
-
Andreas Giesekus and L. M. Falicov
- Subjects
Physics ,symbols.namesake ,Condensed matter physics ,Silicon ,chemistry ,Semiconductor materials ,symbols ,chemistry.chemical_element ,Germanium ,Spin–orbit interaction ,Hamiltonian (quantum mechanics) ,Ground state - Abstract
Les etats fondamentaux de ces impuretes presentent de petites decompositions. Interpretation de cette structure fine fondee sur un calcul contenant des fonctions (P) de liaisons fortes au sommet de la bande de valence. Le couplage spin-orbite et l'interaction trou-trou sont pris en compte dans cette approche
- Published
- 1990
47. Erratum: Small-crystal approach to ordered semiconductor compounds
- Author
-
Maria A. Davidovich, Belita Koiller, and L. M. Falicov
- Subjects
Crystal ,Materials science ,Semiconductor ,business.industry ,Optoelectronics ,business - Published
- 1990
48. Effects of high magnetic fields on charge-density waves in NbSe3
- Author
-
R. V. Coleman, Hao-An Lu, M. P. Everson, L. M. Falicov, and A. Johnson
- Subjects
Physics ,Condensed matter physics ,Magnetoresistance ,Fermi level ,Quantum oscillations ,Fermi surface ,Magnetic field ,symbols.namesake ,Hall effect ,Condensed Matter::Superconductivity ,Electric field ,symbols ,Condensed Matter::Strongly Correlated Electrons ,Charge density wave - Abstract
The magnetotransport properties of ${\mathrm{NbSe}}_{3}$ in the temperature range below the second charge-density-wave (CDW) onset of 59 K have been studied in magnetic fields up to 230 kG. At liquid-helium temperatures giant magnetoquantum oscillations caused by magnetic breakdown (MB) between the normal Fermi surface (FS) and open orbits on the nested sheets of the FS dominate the magnetotransport and are extremely sensitive to the pinned CDW configuration. Spatial variations in the phase of the pinned CDW change the local Fermi level and CDW gap, giving rise to a distribution of FS cross-sectional areas. These variations in FS cross section and CDW gap produce frequency shifts, amplitude modulations, and beat structures in the quantum oscillations observed in both the magnetoresistance and Hall effect. A model conductivity tensor has been developed describing the open-orbit network and MB interference as well as the closed-orbit contribution. The adjustable parameters of the model are the frequency of oscillation, the frequency-distribution spread \ensuremath{\Delta}F, and critical MB parameter ${\ensuremath{\omega}}_{0}$\ensuremath{\tau}.The model has been used to study the detailed configurations of the pinned CDW in nominally pure ${\mathrm{NbSe}}_{3}$ crystals and in ${\mathrm{NbSe}}_{3}$ crystals doped with Fe, Ni, and Co. Unique fits to the data can be generated, and the resulting FS distributions provide direct information on the local CDW domain structure produced by pinning and repinning the CDW or by deliberately introducing impurities. At temperatures in the range 10--59 K, the oscillation amplitude decreases rapidly as the scattering time decreases, and a new magnetoresistance enhancement is observed. The dc resistance anomaly associated with the CDW is enhanced by up to a factor of 4 in a magnetic field of 226 kG and, if assigned exclusively to FS obliteration, it would require an increase from 60% obliteration at H=0 to 92% at H=227 kG. Accurate measurements also indicate a small increase in the transition temperature of \ensuremath{\sim}0.5 K in a magnetic field of 226 kG. These results have been analyzed in terms of a theory proposed by Balseiro and Falicov in which a transverse magnetic field induces a more perfect nesting of the FS.Magnetic-field modifications of the electronic spectrum at the Fermi level can become large when the cyclotron energy \ensuremath{\Elzxh}${\ensuremath{\omega}}_{c}$ is on the order of the CDW gap \ensuremath{\Delta}. Both the enhancement of the magnetoresistance and the sign change in the Hall effect can be related to this mechanism. In addition to the magnetic-field-induced changes in the static CDW state, studies of the dynamics of CDW motion have also been carried out in magnetic fields up to 230 kG. The magnetoresistance response to the CDW motion can be modeled with equations similar to those of the Bardeen tunneling model. At high electric fields the enhanced magnetoresistance in the range 10--59 K is quenched; in the quantum-oscillation regime the enhanced dc magnetoresistance is quenched while the oscillation amplitude saturates. The large magnetoresistance in the static CDW state allows measurement of the threshold electric field down to low temperatures. For the nominally pure crystals the temperature dependence of ${E}_{T}$ in high magnetic fields follows a thermal-fluctuation model similar to that observed at H=0, and the magnitude of ${E}_{T}$ is not significantly changed from the values observed at H=0. At very low temperatures a departure from the dynamics of the tunneling model can give rise to a large region of zero dynamic resistance. This behavior is observed in the highest-purity crystals and is rapidly modified by impurities. The magnetic field facilitates the study of a large range of both static and dynamic CDW effects at low temperature: A systematic classification has been accomplished. Adequate theoretical models have been developed for several of the effects, although further refinement of the models and additional experimental confirmation are needed.
- Published
- 1990
49. Incommensurable Surface Spin Structure in MnO-Type Antiferromagnets
- Author
-
L. M. Falicov and D. C. Chrzan
- Published
- 1990
- Full Text
- View/download PDF
50. Rhodium rewrites the rules of magnetism
- Author
-
L M Falicov
- Subjects
inorganic chemicals ,Materials science ,Magnetic moment ,Magnetism ,General Physics and Astronomy ,chemistry.chemical_element ,Terbium ,equipment and supplies ,Subatomic scale ,Rhodium ,Nickel ,Nuclear magnetic resonance ,chemistry ,Chemical physics ,Dysprosium ,Condensed Matter::Strongly Correlated Electrons ,human activities ,Cobalt - Abstract
Magnetism in matter is a quantum-mechanical phenomenon. It is common at the atomic or subatomic scale but rare in macroscopic bodies. The majority of atoms in the periodic table, notably the transition metals and rare-earth elements, exhibit a magnetic moment. In contrast, most molecules do not – the oxygen molecule is the best known exception. Only a few solids are magnetic: examples include the transition metals (iron, cobalt and nickel), the rare earths (gadolinium, terbium and dysprosium), and some compounds (the transition-metal and rare-earth oxides in particular).
- Published
- 1993
- Full Text
- View/download PDF
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