The Experts below are selected from a list of 8865 Experts worldwide ranked by ideXlab platform
K.h. Bennemann - One of the best experts on this subject based on the ideXlab platform.
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Calculation of the Elementary Excitations and of the magnetic Excitations in cuprates and Sr2RuO4
Journal of Physics and Chemistry of Solids, 2006Co-Authors: K.h. BennemannAbstract:We assume for simplicity that electrons and holes interact dominantly with spin-fluctuations. Thus, we calculate the Elementary Excitations in hole doped cuprates and within R.P.A. the dynamical susceptibility, in particular the resonance peak resulting as feedback from superconductivity.
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analysis of the Elementary Excitations in high tc cuprates explanation of the new energy scale observed by angle resolved photoemission spectroscopy
Physical Review Letters, 2001Co-Authors: Dirk Manske, I Eremin, K.h. BennemannAbstract:We analyze the energy and momentum dependence of the Elementary Excitations in high- T(c) superconductors resulting from the coupling to spin fluctuations. As a result of the energy dependence of the self-energy Sigma(k,omega), characteristic features occur in the spectral density explaining the "kink" in recent angle-resolved photoemission spectroscopy experiments. We present results for the spectral density A(k,omega) for the feedback of superconductivity on the Excitations, and for the superconducting order parameter Delta(k,omega). These results relate also to inelastic neutron scattering and tunneling experiments and shed important light on the essential ingredients a theory of the Elementary Excitations in the cuprates must contain.
Patrik Ohberg - One of the best experts on this subject based on the ideXlab platform.
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Elementary Excitations of a bose einstein condensate in an effective magnetic field
Physical Review A, 2007Co-Authors: D R Murray, Patrik Ohberg, Stephen M Barnett, Damia GomilaAbstract:We calculate the low-energy Elementary Excitations of a Bose-Einstein condensate in an effective magnetic field. The field is created by the interplay between light beams carrying orbital angular momentum and the trapped atoms [G. Juzelinas et al., Phys. Rev. A 71, 053614 (2005)]. We examine the role of the homogeneous magnetic field, familiar from studies of rotating condensates, and also investigate spectra for vector potentials with a more general radial dependence. We discuss the instabilities which arise and how these may be manifested.
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theory of Elementary Excitations in unstable bose einstein condensates
Physical Review A, 2003Co-Authors: Ulf Leonhardt, Tamas Kiss, Patrik OhbergAbstract:Like classical fluids, quantum gases may suffer from hydrodynamic instabilities. Our paper develops a quantum version of the classical stability analysis in fluids, the Bogoliubov theory of Elementary Excitations in unstable Bose-Einstein condensates. In unstable condensates the excitation modes have complex frequencies. We derive the normalization conditions for unstable modes such that they can serve in a mode decomposition of the noncondensed component. Furthermore, we develop approximative techniques to determine the spectrum and the mode functions. Finally, we apply our theory to sonic horizons - sonic black and white holes. For sonic white holes the spectrum of unstable modes turns out to be intrinsically discrete, whereas black holes may be stable.
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theory of Elementary Excitations in unstable bose einstein condensates
arXiv: Soft Condensed Matter, 2002Co-Authors: Ulf Leonhardt, Tamas Kiss, Patrik OhbergAbstract:Like classical fluids, quantum gases may suffer from hydrodynamic instabilities. Our paper develops a quantum version of the classical stability analysis in fluids, the Bogoliubov theory of Elementary Excitations in unstable Bose-Einstein condensates. In unstable condensates the excitation modes have complex frequencies. We derive the normalization conditions for unstable modes such that they can serve in a mode decomposition of the non-condensed component. Furthermore, we develop approximative techniques to determine the spectrum and the mode functions. Finally, we apply our theory to a sonic white hole and find that the spectrum of unstable modes is intrinsically discrete.
K. I. Kugel - One of the best experts on this subject based on the ideXlab platform.
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Elementary Excitations in the symmetric spin-orbital model
Jetp Letters, 2014Co-Authors: M. Yu. Kagan, K. I. Kugel, A. V. Mikheyenkov, A. F. BarabanovAbstract:Possible types of Elementary Excitations in the symmetric spin-orbital model on a square lattice are analyzed using a spherically symmetric self-consistent approach. The excitation spectra are calculated. The behavior of the corresponding correlation functions depending on the temperature and parameters of the model is studied. A schematic phase diagram is plotted. It is shown that the thermodynamics of the system is mainly determined by Elementary Excitations with the entangled spin and orbital degrees of freedom.
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Elementary Excitations in the coupled spin-orbital model
Physical Review B, 1998Co-Authors: J. Van Den Brink, W. Stekelenburg, D. I. Khomskii, G.a Sawatzky, K. I. KugelAbstract:The Elementary Excitations of a model Hamiltonian that captures the low-energy behavior of a simple twofold-degenerate Hubbard Hamiltonian, with Hund’s rule coupling, is studied. The phase diagram in the mean-field limit and in a two-site approach reveals a rich variety of phases where both the orbital and the spin degrees of freedom are ordered. We show that, besides the usual spin waves ~magnons!, there also exist orbital waves ~orbitons! and, most interestingly, in a completely ferromagnetically coupled system, a combined spinorbital excitation which can be visualized as a bound state of magnons and orbitons. For a completely degenerate system the bound states are found to be the lowest-lying Elementary Excitations, both in one and two dimensions. Finally we extend our treatment to almost-degenerate systems. This can serve as an example that Elementary Excitations in orbitally degenerate strongly correlated electron systems in general carry both spin and orbital character. @S0163-1829~98!10839-1#
Matthias Troyer - One of the best experts on this subject based on the ideXlab platform.
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Elementary Excitations of the Symmetric Spin-Orbital Model: The XY Limit
Physical Review Letters, 1999Co-Authors: Frédéric Mila, Beat Frischmuth, Andreas Deppeler, Matthias TroyerAbstract:The Elementary Excitations of the 1D, symmetric, spin-orbital model are investigated by studying two anisotropic versions of the model, the pure XY and the dimerized XXZ case, with analytical and numerical methods. While they preserve the symmetry between spin and orbital degrees of freedom, these models allow for a simple and transparent picture of the low--lying Excitations: In the pure XY case, a phase separation takes place between two phases with free--fermion like, gapless Excitations, while in the dimerized case, the low-energy effective Hamiltonian reduces to the 1D Ising model with gapped Excitations. In both cases, all the Elementary Excitations involve simultaneous flips of the spin and orbital degrees of freedom, a clear indication of the breakdown of the traditional mean-field theory.
Tamas Kiss - One of the best experts on this subject based on the ideXlab platform.
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theory of Elementary Excitations in unstable bose einstein condensates
Physical Review A, 2003Co-Authors: Ulf Leonhardt, Tamas Kiss, Patrik OhbergAbstract:Like classical fluids, quantum gases may suffer from hydrodynamic instabilities. Our paper develops a quantum version of the classical stability analysis in fluids, the Bogoliubov theory of Elementary Excitations in unstable Bose-Einstein condensates. In unstable condensates the excitation modes have complex frequencies. We derive the normalization conditions for unstable modes such that they can serve in a mode decomposition of the noncondensed component. Furthermore, we develop approximative techniques to determine the spectrum and the mode functions. Finally, we apply our theory to sonic horizons - sonic black and white holes. For sonic white holes the spectrum of unstable modes turns out to be intrinsically discrete, whereas black holes may be stable.
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theory of Elementary Excitations in unstable bose einstein condensates
arXiv: Soft Condensed Matter, 2002Co-Authors: Ulf Leonhardt, Tamas Kiss, Patrik OhbergAbstract:Like classical fluids, quantum gases may suffer from hydrodynamic instabilities. Our paper develops a quantum version of the classical stability analysis in fluids, the Bogoliubov theory of Elementary Excitations in unstable Bose-Einstein condensates. In unstable condensates the excitation modes have complex frequencies. We derive the normalization conditions for unstable modes such that they can serve in a mode decomposition of the non-condensed component. Furthermore, we develop approximative techniques to determine the spectrum and the mode functions. Finally, we apply our theory to a sonic white hole and find that the spectrum of unstable modes is intrinsically discrete.