9,356 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
Finite-time singularities in f(R, T) gravity and the effect of conformal anomaly
We investigate gravity models ( is the curvature scalar and
is the trace of the stress-energy tensor of ordinary matter) that are able to
reproduce the four known types of future finite-time singularities. We choose a
suitable expression for the Hubble parameter in order to realise the cosmic
acceleration and we introduce two parameters, and , which
characterise each type of singularity. We address conformal anomaly and we
observe that it cannot remove the sudden singularity or the type IV one, but,
for some values of , the big rip and the type III singularity may be
avoided. We also find that, even without taking into account conformal anomaly,
the big rip and the type III singularity may be removed thanks to the presence
of the contribution of the theory.Comment: 18 pages; Accepted for publication in Canadian Journal of Physics
(CJP
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
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