2,427 research outputs found

    Non-local composite spin-lattice polarons in high temperature superconductors

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    The non-local nature of the polaron formation in t-t'-t"-J model is studied in large lattices up to 64 sites by developing a new numerical method. We show that the effect of longer-range hoppings t' and t" is a large anisotropy of the electron-phonon interaction (EPI) leading to a completely different influence of EPI on the nodal and antinodal points in agreement with the experiments. Furthermore, nonlocal EPI preserves polaron's quantum motion, which destroys the antiferromagnetic order effectively, even at strong coupling regime, although the quasi-particle weight in angle-resolved-photoemission spectroscopy is strongly suppressed.Comment: 5 pages, 4 figure

    Quantum Dynamics of the Hubbard-Holstein Model in Equilibrium and Non-Equilibrium: Application to Pump-Probe Phenomena

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    The spectral response and physical features of the 2D Hubbard-Holstein model are calculated both in equilibrium at zero and low chemical dopings, and after an ultra short powerful light pulse, in undoped systems. At equilibrium and at strong charge-lattice couplings, the optical conductivity reveals a 3-peak structure in agreement with experimental observations. After an ultra short pulse and at nonzero electron-phonon interaction, phonon and spin subsystems oscillate with the phonon period Tph≈80T_{ph} \approx 80 fs. The decay time of the phonon oscillations is about 150-200 fs, similar to the relaxation time of the charge system. We propose a criterion for observing these oscillations in high TcT_c compounds: the time span of the pump light pulse τpump\tau_{pump} has to be shorter than the phonon oscillation period TphT_{ph}.Comment: 4 pages, 4 figure

    Polaron features for long-range electron-phonon interaction

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    The polaron features for long-range electron-phonon interaction are investigated by extending a variational approach previously proposed for the study of systems with local coupling. The ground-state spectral weight, the average kinetic energy, the mean number of phonons, and the electron-lattice correlation function are discussed for a wide range of model parameters focusing on the adiabatic regime and comparing the results with the short-range case (Holstein model). A strong mixing of electronic and phononic degrees of freedom for small values of the electron-phonon coupling constant is found in the adiabatic case due to the long-range interaction. Finally a polaron "phase diagram" is proposed.Comment: 4 figs., to appear in J. Phys.:Condens. Matte

    Evolution of magnetic phases and orbital occupation in (SrMnO3)n/(LaMnO3)2n superlattices

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    The magnetic and electronic modifications induced at the interfaces in (SrMnO3_{3})n_{n}/(LaMnO3_{3})2n_{2n} superlattices have been investigated by linear and circular magnetic dichroism in the Mn L2,3_{2,3} x-ray absorption spectra. Together with theoretical calculations, our data demonstrate that the charge redistribution across interfaces favors in-plane ferromagnetic (FM) order and eg(x2−y2)e_{g}(x^{2}-y^{2}) orbital occupation, in agreement with the average strain. Far from interfaces, inside LaMnO3_3, electron localization and local strain favor antiferromagnetism (AFM) and eg(3z2−r2)e_{g}(3z^{2}-r^{2}) orbital occupation. For n=1n=1 the high density of interfacial planes ultimately leads to dominant FM order forcing the residual AFM phase to be in-plane too, while for n≥5n \geq 5 the FM layers are separated by AFM regions having out-of-plane spin orientation.Comment: accepted for publication as a Rapid Communication in Physical Review

    The CMS Monte Carlo Production System: Development and Design

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    The CMS production system has undergone a major architectural upgrade from its predecessor, with the goal of reducing the operational manpower needed and preparing for the large scale production required by the CMS physics plan. The new production system is a tiered architecture that facilitates robust and distributed production request processing and takes advantage of the multiple Grid and farm resources available to the CMS experiment
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