8,343 research outputs found
Evidence of quantum criticality in the doped Haldane system Y2BaNiO5
Experimental bulk susceptibility X(T) and magnetization M(H,T) of the
S=1-Haldane chain system doped with nonmagnetic impurities, Y2BaNi1-xZnxO5
(x=0.04,0.06,0.08), are analyzed. A numerical calculation for the low-energy
spectrum of non-interacting open segments describes very well experimental data
above 4 K. Below 4 K, we observe power-law behaviors, X(T)=T^-alpha and
M(H,T)/T^(1-alpha)=f(alpha,(H/T)), with alpha (<1) depending on the doping
concentration x.This observation suggests the appearance of a gapless quantum
phase due to a broad distribution of effective couplings between the
dilution-induced moments.Comment: 4 pages, 3 figure
Topological Confinement and Superconductivity
We derive a Kondo Lattice model with a correlated conduction band from a
two-band Hubbard Hamiltonian. This mapping allows us to describe the emergence
of a robust pairing mechanism in a model that only contains repulsive
interactions. The mechanism is due to topological confinement and results from
the interplay between antiferromagnetism and delocalization. By using
Density-Matrix-Renormalization-Group (DMRG), we demonstrate that this mechanism
leads to dominant superconducting correlations in a 1D-system.Comment: 4 pages, 4 figure
Effective Low-Energy Model for f-Electron Delocalization
We consider a Periodic Anderson Model (PAM) with a momentum-dependent
inter-band hybridization that is strongly suppressed near the Fermi level.
Under these conditions, we reduce the PAM to an effective low-energy
Hamiltonian, , by expanding in the small parameter (
is the maximum inter-band hybridization amplitude and is the hopping
integral of the broad band). The resulting model consists of a t-J f-band
coupled via the Kondo exchange to the electrons in the broad band. allows for studying the f-electron delocalization transition. The result
is a doping-induced Mott transition for the f-electron delocalization, which we
demonstrate by density-matrix renormalization group (DMRG) calculations
Orbital disorder induced by charge fluctuations in vanadium spinels
Motivated by recent experiments on vanadium spinels, VO, that show
an increasing degree of electronic delocalization for smaller cation sizes, we
study the evolution of orbital ordering (OO) between the strong and
intermediate-coupling regimes of a multi-orbital Hubbard Hamiltonian. The
underlying magnetic ordering of the Mott insulating state leads to a rapid
suppression of OO due to enhanced charge fluctuations along ferromagnetic
bonds. Orbital double-occupancy is rather low at the transition point
indicating that the system is in the crossover region between strong and
intermediate-coupling regimes when the orbital degrees of freedom become
disordered
Matéria seca e macronutrientes em mudas de melancia afetados pelo substrato.
Neste trabalho avaliaram-se a matéria seca, os teores e coeficientes de utilização biológica (CUB) de macronutrientes em mudas de melancia sob diferentes substratos
Complementary action of chemical and electrical synapses to perception
Acknowledgements This study was possible by partial financial support from the following agencies: Fundação Araucária, EPSRC-EP/I032606/1, CNPq No. 441553/2014-1, CAPES No. 17656-12-5 and Science Without Borders Program— Process Nos. 17656125, 99999.010583/2013-00 and 245377/2012-3.Peer reviewedPostprin
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