23,115 research outputs found
Coherence scale of the two-dimensional Kondo Lattice model
A doped hole in the two-dimensional half-filled Kondo lattice model with
exchange J and hopping t has momentum (pi,pi) irrespective of the coupling J/t.
The quasiparticle residue of the doped hole, Z_{(\pi, \pi)}, tracks the Kondo
scale, T_K, of the corresponding single impurity model. Those results stem from
high precision quantum Monte Carlo simulations on lattices up to 12 X 12.
Accounting for small dopings away from half-filling within a rigid band
approximation, this result implies that the effective mass of the charge
carriers at the Fermi level tracks 1/T_K or equivalently that the coherence
temperature T_{coh} \propto T_K. This results is consistent with the large-N
saddle point of the SU(N) symmetric Kondo lattice model.Comment: 4 pages, 4 figure
Fermi arcs and pseudogap emerging from dimensional crossover at the Fermi surface in LaSrCuO
The doping mechanism and realistic Fermi surface (FS) evolution of
LaSrCuO (LSCO) are modelled within an extensive ab-initio
framework including advanced band-unfolding techniques. We show that ordinary
Kohn-Sham DFT+U can reproduce the observed metal-insulator transition, when not
restricted to the paramagnetic solution space. Arcs are self-doped by orbital
charge transfer within the Cu-O planes, while the introduced Sr charge is
strongly localized. Arc protection and the inadequacy of the rigid-band picture
are consequences of a rapid change in orbital symmetry at the Fermi energy: the
material undergoes a dimensional crossover along the Fermi surface, between the
nodal (2D) and antinodal (3D) regions. In LSCO, this crossover accounts for FS
arcs, the antinodal pseudogap, and insulating behavior in -axis
conductivity, all ubiquitous phenomena in high-T cuprates. Ligand Coulomb
integrals involving out-of-plane sites are principally responsible for the most
striking effects observed by ARPES in LSCO.Comment: Final slightly expanded version, as accepted in EP
Optimizing the speed of a Josephson junction
We review the application of dynamical mean-field theory to Josephson
junctions and study how to maximize the characteristic voltage IcRn which
determines the width of a rapid single flux quantum pulse, and thereby the
operating speed in digital electronics. We study a wide class of junctions
ranging from SNS, SCmS (where Cm stands for correlated metal), SINIS (where the
insulating layer is formed from a screened dipole layer), and SNSNS structures.
Our review is focused on a survey of the physical results; the formalism has
been developed elsewhere.Comment: (36 pages, 15 figures, to appear in Int. J. Mod. Phys. B
Noise control by sonic crystal barriers made of recycled materials
A systematic study of noise barriers based on sonic crystals made of
cylinders that use recycled materials like absorbing component is here
reported. The barriers consist of only three rows of perforated metal shells
filled with rubber crumb. Measurements of reflectance and transmittance by
these barriers are reported. Their attenuation properties result from a
combination of sound absorption by the rubber crumb and reflection by the
periodic distribution of scatterers. It is concluded that porous cylinders can
be used as building blocks whose physical parameters can be optimized in order
to design efficient barriers adapted to different noisy environments
From the Fermi Liquid Towards the Wigner Solid in Two Dimensions
The quantum-classical crossover from the Fermi liquid towards the Wigner
solid is numerically revisited, considering small square lattice models where
electrons interact via a Coulomb U/r potential. We review a series of exact
numerical results obtained in the presence of weak site disorder for fully
polarized electrons (spinless fermions) and when the spin degrees of freedom
are included. A novel intermediate regime between the Fermi system of weakly
interacting localized particles and the correlated Wigner solid is obtained. A
detailed analysis of the non disordered case shows that the intermediate ground
state is a solid entangled with an excited liquid. For electrons in two
dimensions, this raises the question of the existence of an unnoticed
intermediate liquid-solid phase. Using the Coulomb energy to kinetic energy
ratio r_s ~ U ~ n_s^{-1/2}, we discuss certain analogies between the numerical
results obtained as a function of U for a few particles and the low temperature
behaviors obtained as a function of the carrier density n_s in two dimensional
electron gases. Notably, the new ``exotic state of matter'' numerically
observed at low energies in small clusters occurs at the same intermediate
ratios r_s than the unexpected low temperature metallic behavior characterizing
dilute electron gases. The finite size effects in the limit of strong disorder
are eventually studied in the last section, providing two numerical evidences
that the weak coupling Fermi limit is delimited by a second order quantum phase
transition when one increases U.Comment: 45 pages, review article to appear in ``Exotic states in Quantum
Nanostructures'' ed. S. Sarkar, Kluwer, Dordrech
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