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- Hubbard Model (4)
- Ground State (3)
- Trans-polyacetylene (3)
- Optical Properties (2)
- Peierls Mechanism (2)
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- Alternative Feynman-Diagram Method (1)
- Antiferromagnets (1)
- Auger Spectra (1)
- Auxiliary Particle Methods (1)
- Band Structure (1)
- Band-Structure Method (1)
- Current-Driven Domain Wall Motion (1)
- Current-Spin Coupling (1)
- Density Functionals (1)
- Electromagnetic Pulses (1)
- Electron Paramagnetic Resonance (1)
- Electronic-Structure Analysis (1)
- Errata (1)
- Ferromagnetic Domain Walls (1)
- Fine Wires (1)
- Flux Flow Spectroscopy (1)
- Flux States (1)
- Fumi’s Theorem (1)
- GGA (1)
- General-Spin Kondo Problem (1)
- Generalized-Gradient-Approximation (1)
- Infinite-U Limit (1)
- Infinite-U Mean-Field Theory (1)
- Intermediate Spin (1)
- Kondo Effect (1)
Articles 1 - 24 of 24
Full-Text Articles in Atomic, Molecular and Optical Physics
Color Changes In Stochastic Light Fields Propagating In Non-Kolmogorov Turbulence, Olga Korotkova, Elena Shchepakina
Color Changes In Stochastic Light Fields Propagating In Non-Kolmogorov Turbulence, Olga Korotkova, Elena Shchepakina
Physics Articles and Papers
The dependence of spectral shifts and switches in optical stochastic beams propagating through nonclassic turbulent medium on the slope of the power spectrum of fluctuations in the refractive index is revealed.
Spatio-Temporal Coupling Of Random Electromagnetic Pulses Interacting With Reflecting Gratings, Min Yao, Yangjian Cai, Olga Korotkova, Qiang Lin, Zhaoying Wang
Spatio-Temporal Coupling Of Random Electromagnetic Pulses Interacting With Reflecting Gratings, Min Yao, Yangjian Cai, Olga Korotkova, Qiang Lin, Zhaoying Wang
Physics Articles and Papers
Matrix optics is applied to a class of random, in time and space, electromagnetic pulsed beam-like (REMPB) radiation interacting with linear optical elements. A 66 order matrix describing transformation of a six-dimensional state vector including four spatial and two temporal positions within the field is used to derive conditions for spatio-temporal coupling. An example is included which deals with a spatio-temporal coupling in a typical REMPB on reflection from a reflecting grating. Electromagnetic nature of such interaction is explored via considering dependence of the degree of polarization of the reflected REMPB on its source and on the structure of the …
Comment On “Theory Of Current-Driven Domain Wall Motion: Spin Transfer Versus Momentum Transfer”, S. E. Barnes
Comment On “Theory Of Current-Driven Domain Wall Motion: Spin Transfer Versus Momentum Transfer”, S. E. Barnes
Physics Articles and Papers
A Comment on the Letter by Gen Tatara and Hiroshi Kohno, Phys. Rev. Lett. 92 086601 (2004). The authors of the Letter offer a Reply.
Current-Spin Coupling For Ferromagnetic Domain Walls In Fine Wires, S. E. Barnes, S. Maekawa
Current-Spin Coupling For Ferromagnetic Domain Walls In Fine Wires, S. E. Barnes, S. Maekawa
Physics Articles and Papers
The coupling between a current and a domain wall is examined. In the presence of a finite current and in the absence of a potential which breaks the translational symmetry, there is a perfect transfer of angular momentum from the conduction electrons to the wall. As a result, the ground state is in uniform motion and this remains the case even when relaxation is included. This is described by, appropriately modified, Landau-Lifshitz-Gilbert equations. The results for a simple pinning model are compared with experiment.
Intermediate Spin, Schrödinger Cat States, And Nanomagnets, S. E. Barnes
Intermediate Spin, Schrödinger Cat States, And Nanomagnets, S. E. Barnes
Physics Articles and Papers
Quantum tunneling in nanomagnets finds a natural description in terms of intermediate spin. Periodic magnetic effects correspond to a change of flux by the flux quantum Φ0. Schrödinger cat states with different superpositions of the applied magnetic field occur. The molecular magnet Fe8 is discussed and new effects are predicted for Mn12.
Quantum Coherence In Small Antiferromagnets, S. E. Barnes, R. Ballou, B. Barbara, J. Strelen
Quantum Coherence In Small Antiferromagnets, S. E. Barnes, R. Ballou, B. Barbara, J. Strelen
Physics Articles and Papers
An antiferromagnetic particle with an excess spin j⃗ has 2 degrees of freedom. The one associated with j⃗ is ferromagnetic, while the antiferromagnetic behavior involves Néel vector n⃗. It is shown that the spin-parity effect described by Loss et al. has to do with the ferromagnetic degree of freedom and does not imply the localization of n⃗ for small enough particles for half-integer spin. It is also shown that the tunnel splitting associated with n⃗ is insensitive to applied fields.
The Possibility Of Flux Flow Spectroscopy, S. E. Barnes, J. L. Cohn, F. Zuo
The Possibility Of Flux Flow Spectroscopy, S. E. Barnes, J. L. Cohn, F. Zuo
Physics Articles and Papers
A novel spectroscopic technique applicable to the study of spin excitations in magnetic materials is described. The probe frequency and wave vector are determined by the moving Abrikosov flux lattice of a type II superconductor in the mixed state. The feasibility of employing oxide superconductors and relevant material parameters are discussed.
Implications Of Fumi’S Theorem For Auxiliary Particle Methods, S. E. Barnes
Implications Of Fumi’S Theorem For Auxiliary Particle Methods, S. E. Barnes
Physics Articles and Papers
Fumi’s theorem in conjunction with some general theorems associated with auxiliary particle methods dictates the functional form of the on-shell auxiliary particle self-energy Σ for a certain class of impurity scattering problems. An explicit calculation which confirms the result is described and the implications for various approaches to the Kondo effect discussed.
Auger Spectra And Band Structure Of La1.85Sr0.15Cuo4 And La1.85Ba0.15Cuo4, R. Bar-Deroma, J. Felsteiner, R. Brener, J. Ashkenazi, D. Van Der Marel
Auger Spectra And Band Structure Of La1.85Sr0.15Cuo4 And La1.85Ba0.15Cuo4, R. Bar-Deroma, J. Felsteiner, R. Brener, J. Ashkenazi, D. Van Der Marel
Physics Articles and Papers
High-resolution Auger electron spectra of La1.85Sr0.15CuO4 and La1.85Ba0.15CuO4 have been measured. The experimental Auger line shapes of the oxygen KLL and copper L2,3VV transitions are compared with those generated from local-density-approximation linear-muffin-tin-orbital band-structure calculations. An analysis based on this comparison is used to determine the Coulomb parameters Up and Ud of the oxygen and copper atoms, respectively. For this purpose, an extended version of Cini and Sawatzky’s expression for the theoretical Auger line shape is used, taking into account the multiplet structure of the Auger final …
Magnetism With Generalized-Gradient-Approximation Density Functionals, D.J. Singh, J. Ashkenazi
Magnetism With Generalized-Gradient-Approximation Density Functionals, D.J. Singh, J. Ashkenazi
Physics Articles and Papers
We report generalized-gradient-approximation (GGA) density-functional studies of Cr, V, and Pd, using an all-electron, general-potential linearized-augmented-plane-wave technique. These calculations were undertaken in order to assess the utility of the GGA as an improvement over the local-density approximation in describing transition-metal magnetism. It is found that although the tendency towards magnetism is enhanced, both V and Pd are correctly predicted to be nonmagnetic with the recent GGA functional of Perdew (PW GGA-II) as with the Langreth-Mehl-Hu (LM) functional. Calculations for commensurate antiferromagnetic Cr show that the PW GGA-II predicts an overly large moment of 1.4μB while the LM functional yields …
Nonuniversality In The Kondo Effect, M. Naghashpour, S. E. Barnes
Nonuniversality In The Kondo Effect, M. Naghashpour, S. E. Barnes
Physics Articles and Papers
We have analytically evaluated, up to fourth order, all logarithmic terms in the perturbation expansion of the magnetization scrM for the Kondo model. All nonlogarithmic terms have been evaluated up to third order. When these results are compared with the claimed universal function scrM(H/TH) calculated with the Bethe ansatz, we find that the two cannot be made to agree whatever the form of TH. We conclude that such universal functions do not exist.
Resistivity And Thermoelectric-Power Measurements Of PrXY1-XBa2Cu3O7-Δ Up To 1200 K And An Electronic-Structure Analysis, B. Fisher, J. Genossar, L. Patlagan, J. Ashkenazi
Resistivity And Thermoelectric-Power Measurements Of PrXY1-XBa2Cu3O7-Δ Up To 1200 K And An Electronic-Structure Analysis, B. Fisher, J. Genossar, L. Patlagan, J. Ashkenazi
Physics Articles and Papers
We report measurements of absolute thermoelectric power and resistivity in PrxY1-xBa2Cu3O7-δ, as function of x and δ, over a wide temperature range. At high temperature, the substitution of Pr for Y does not affect the thermopower and resistivity; Pr behaves then as a trivalent ion: Pr3+. For small x and δ the effects of substitution of Y by Pr and of oxygen deficiency on the low-temperature resistivity are additive. A simple electronic-structure model is proposed to account for thermopower as function of temperature, x, and δ.
Flux States For The Infinite-U Limit Of The Hubbard Model, S. E. Barnes
Flux States For The Infinite-U Limit Of The Hubbard Model, S. E. Barnes
Physics Articles and Papers
For finite doping, δ, relative to half filling, it is shown, within the confines of a mean-field auxiliary-operator formulation, for the strictly infinite-U, i.e., J=0, limit of the two-dimensional Hubbard model, that the spinons generate a fictitious magnetic flux to which holons are subject and vice versa. For small doping, a flux state is the absolute ground state and has 1-δ=2p/q, where p/q is a rational fraction and the flux per plaquette is Φ=(p/q)Φ0, where Φ0 is the flux quantum. This phenomenon can be viewed upon as an all-electron Peierls instability or as broken statistical symmetry.
All-Electronic Peierls Instability In The Infinite-U Mean-Field Theory For The Hubbard Model, S. E. Barnes
All-Electronic Peierls Instability In The Infinite-U Mean-Field Theory For The Hubbard Model, S. E. Barnes
Physics Articles and Papers
It is shown, for a small hole doping relative to half filling, that the large-U limit of the Hubbard model (or J=0 limit of the t-J model) exhibits an all-electron Peierls instability towards a state with a charge-density wave. The resulting gap in the spinon spectrum renders the model an insulator.
Spin-Disordered Ground State For A Nearly Half-Filled Hubbard Model, S. E. Barnes
Spin-Disordered Ground State For A Nearly Half-Filled Hubbard Model, S. E. Barnes
Physics Articles and Papers
Following Nagaoka, the ground state of the large-U nearly half-filled Hubbard model is ‘‘ferromagnetic.’’ However, because of the anisotropic exchange energy JA, the physical Nagaoka ground state is nondegenerate and comprises a totally disordered spin state, i.e., a linear combination of all possible spin arrangements. For this ground state the susceptibility is Pauli-like but of a magnitude associated with a narrow band of width ∼JA while the holons, i.e., the charge excitations, correspond to spinless fermions with a band of width 2zt. Associated with the spinon sector are very poorly defined spin waves, i.e., bosons, with a …
Application Of The Linear Muffin-Tin-Orbital Band-Structure Method To Calculate Optical Properties Of Solids, R. Zemach, J. Ashkenazi, E. Ehrenfreund
Application Of The Linear Muffin-Tin-Orbital Band-Structure Method To Calculate Optical Properties Of Solids, R. Zemach, J. Ashkenazi, E. Ehrenfreund
Physics Articles and Papers
Optical matrix elements have been derived for crystals by applying the theory of optical transitions within the formalism of the linear muffin-tin-orbital band-structure method and using Racah algebra. A Brillouin-zone integration by the tetrahedron method allows straightforward numerical computation of the optical function ε2(ω) [or σ(ω)]. Other optical functions may be derived by using a Kramers-Kronig analysis.
Calculation Of Optical Properties Of Trans-Polyacetylene By The Linear Muffin-Tin-Orbital Method, R. Zemach, J. Ashkenazi, E. Ehrenfreund
Calculation Of Optical Properties Of Trans-Polyacetylene By The Linear Muffin-Tin-Orbital Method, R. Zemach, J. Ashkenazi, E. Ehrenfreund
Physics Articles and Papers
The basic optical properties of trans-(CH)x in the P21/n and the P21/a space groups are derived from first principles. The relevant optical matrix elements are calculated within the self-consistent linear muffin-tin-orbital band-structure method. The derived optical response functions are compared with the results from a variety of optical as well as electron-energy-loss experimental studies. It is shown that the measured optical constants are consistent with the P21/n structure.
Ground State Of Trans-Polyacetylene And The Peierls Mechanism - Ashkenazi Et Al. Reply, J. Ashkenazi, W. E. Pickett, H. Krakauer, C. S. Wang, B. M. Klein, S. R. Chubb
Ground State Of Trans-Polyacetylene And The Peierls Mechanism - Ashkenazi Et Al. Reply, J. Ashkenazi, W. E. Pickett, H. Krakauer, C. S. Wang, B. M. Klein, S. R. Chubb
Physics Articles and Papers
Ashkenazi et al. reply to Original Article: J. Ashkenazi, W. E. Pickett, H. Krakauer, C. S. Wang, B. M. Klein, and S. R. Chubb, Ground state of trans-polyacetylene and the Peierls mechanism, Physical Review Letters 62, 2016 (1989).
Ground State Of Trans-Polyacetylene And The Peierls Mechanism - Errata, J. Ashkenazi, W. E. Pickett, H. Krakauer, C. S. Wang, B. M. Klein, S. R. Chubb
Ground State Of Trans-Polyacetylene And The Peierls Mechanism - Errata, J. Ashkenazi, W. E. Pickett, H. Krakauer, C. S. Wang, B. M. Klein, S. R. Chubb
Physics Articles and Papers
Errata to Original Article: J. Ashkenazi, W. E. Pickett, H. Krakauer, C. S. Wang, B. M. Klein, and S. R. Chubb, Ground state of trans-polyacetylene and the Peierls mechanism, Physical Review Letters, 62, 2016 (1989).
Ground State Of Trans-Polyacetylene And The Peierls Mechanism, J. Ashkenazi, W. E. Pickett, H. Krakauer, C. S. Wang, B. M. Klein, S. R. Chubb
Ground State Of Trans-Polyacetylene And The Peierls Mechanism, J. Ashkenazi, W. E. Pickett, H. Krakauer, C. S. Wang, B. M. Klein, S. R. Chubb
Physics Articles and Papers
It is shown formally that the Peierls expression is inadequate for studying the instabilities of a physically realizable one-dimensional chain of atoms, due to the long-range nature of the Coulomb interaction. Detailed total-energy studies of trans-polyacetylene, for both suggested crystal structures (P21/n,P21/a) and for the one-dimensional chain, establish that no appreciable total-energy minimum occurs for nonzero dimerization amplitude within the local-density approximation. The measured dimerization is discussed within the context of recent models of electron correlation.
Excitations In A Nearly Half-Filled Hubbard Model With U=∞, S. E. Barnes
Excitations In A Nearly Half-Filled Hubbard Model With U=∞, S. E. Barnes
Physics Articles and Papers
It is shown that, even near half filling, the elementary excitations of the large-U Hubbard model form wide bands of width ∼t, the intersite hopping integral, and that the slave-boson-based mean-field approximation is qualitatively wrong in the relevant limit. This large-U limit has no Kondo-type divergences.
Alternative Feynman-Diagram Method For The General-Spin Kondo Problem, S. E. Barnes
Alternative Feynman-Diagram Method For The General-Spin Kondo Problem, S. E. Barnes
Physics Articles and Papers
We introduce a new method of replacing spin operators with pseudofermions. For a spin value S there are 2S pseudofermions each of which can have spin ‘‘up’’ or ‘‘down’’. In contrast to the standard Abrikosov method which has 2S+1 inequivalent fermions, i.e., one for each Sz value, the present pairs are all equivalent. It follows that the general spin expression is obtained by multiplying the S=(1/2 result by a ceratin combinational factor. This aids in the construction of rotationally invariant solutions for the general-spin Kondo problem for the case when n≤2S, where n is the number of conduction-electron scattering …
Electron Paramagnetic Resonance Of Gd3+ Ions In The Superconductor Gdba2Cu3OX, F. Mehran, S. E. Barnes, C. C. Tsuei, T. R. Mcguire
Electron Paramagnetic Resonance Of Gd3+ Ions In The Superconductor Gdba2Cu3OX, F. Mehran, S. E. Barnes, C. C. Tsuei, T. R. Mcguire
Physics Articles and Papers
EPR from Gd3+ ions in the high-Tc≃90 K superconductor GdBa2Cu3Ox is reported. The temperature dependence of the linewidth and intensity of the Gd3+ ions in the vicinity of Tc are related to the corresponding characteristics of the Cu2+ ions.
Observation Of Al2O3: Cr3+ Magnetic Resonance Via Solitons In Long Josephson Junctions, F. Mehran, S. E. Barnes, C. C. Chi, R. L. Sandstrom, C. P. Umbach
Observation Of Al2O3: Cr3+ Magnetic Resonance Via Solitons In Long Josephson Junctions, F. Mehran, S. E. Barnes, C. C. Chi, R. L. Sandstrom, C. P. Umbach
Physics Articles and Papers
We have detected the zero-field electron-spin resonance signal of Al2O3 with ∼1000 ppm Cr3+ using an edge Josephson junction. The sample comprises the substrate upon which the junction was fabricated and the coupling to the electron-spin resonance is via the solitons which exist in these "long" devices.