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49

Sep 18, 2013
09/13

by
E. Plekhanov; A. Avella; F. Mancini

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By using Density Matrix Renormalization Group (DMRG) technique we study the 1D extended anisotropic Heisenberg model. We find that starting from the ferromagnetic phase, the system undergoes two quantum phase transitions (QPTs) induced by frustration. By increasing the next-nearest-neighbor (NNN) interaction, the ground state of the system changes smoothly from a completely polarized state to a NNN correlated one. On the contrary, letting the in-plane interaction to be greater than the...

Source: http://arxiv.org/abs/0705.4361v1

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44

Sep 18, 2013
09/13

by
E. Plekhanov; S. Sorella; M. Fabrizio

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We study by Variational Monte Carlo an extended Hubbard model away from half filled band density which contains two competing nearest-neighbor interactions: a superexchange $J$ favoring d-wave superconductivity and a repulsion $V$ opposing against it. We find that the on-site repulsion $U$ effectively enhances the strength of $J$ meanwhile suppressing that of $V$, thus favoring superconductivity. This result shows that attractions which do not involve charge fluctuations are very well equipped...

Source: http://arxiv.org/abs/cond-mat/0210169v2

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65

Sep 18, 2013
09/13

by
E. Plekhanov; A. Avella; F. Mancini

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We present a study of entanglement in the case of the 1D extended anisotropic Heisenberg model. We investigate two quantum phase transitions (QPTs) within the previously found ergodicity phase diagram [E. Plekhanov, A. Avella, and F. Mancini Phys. Rev. B \textbf{74}, 115120 (2006)]. Our calculations are done by means of the numerically exact Lanczos method at T=0, followed by a finite-size scaling. As a measure of entanglement we use the concurrence for two spins out of the system. We conclude...

Source: http://arxiv.org/abs/0705.4413v1

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46

Sep 18, 2013
09/13

by
F. Mancini; E. Plekhanov; G. Sica

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In this paper we present for the first time the exact solution in the narrow-band limit of the 1D extended Hubbard model with nearest-neighbour spin-spin interactions described by an exchange constant J. An external magnetic field h is also taken into account. This result has been obtained in the framework of the Green's functions formalism, using the Composite Operator Method. By means of this theoretical background, we have studied some relevant features such as double occupancy,...

Source: http://arxiv.org/abs/1211.6551v1

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50

Sep 19, 2013
09/13

by
E Plekhanov; A Avella; F Mancini; F P Mancini

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The orbital degrees of freedom are of vital importance in explanation of various phenomena. Among them is the orbital-selective Mott transition (OSMT), which is thought to occur in several materials as Ca$_{2-x}$Sr$_x$RuO$_4$ and La$_{n+1}$Ni${_n}$O$_{3n+1}$. OSMT is usually studied in the infinite-dimension limit, and for the time being, it is not clear if it could survive in one-dimensional (1D) case. There exist two scenarios for the OSMT: upon increasing the interaction in a two-band system...

Source: http://arxiv.org/abs/1009.4448v1