11,344 research outputs found
Bosonization and density-matrix renormalization group studies of Fulde-Ferrell-Larkin-Ovchinnikov phase and irrational magnetization plateaus in coupled chains
We review the properties of two coupled fermionic chains, or ladders, under a
magnetic field parallel to the lattice plane. Results are computed by
complementary analytical (bosonization) and numerical (density-matrix
renormalization group) methods which allows a systematic comparison. Limiting
cases such as coupled bands and coupled chains regimes are discussed. We
particularly focus on the evolution of the superconducting correlations under
increasing field and on the presence of irrational magnetization plateaus. We
found the existence of large doping-dependent magnetization plateaus in the
weakly-interacting and strong-coupling limits and in the non-trivial case of
isotropic couplings. We report on the existence of extended
Fulde-Ferrell-Larkin-Ovchinnikov phases within the isotropic t-J and Hubbard
models, deduced from the evolution of different observables under magnetic
field. Emphasis is put on the variety of superconducting order parameters
present at high magnetic field. We have also computed the evolution of the
Luttinger exponent corresponding to the ungaped spin mode appearing at finite
magnetization. In the coupled chain regime, the possibility of having polarized
triplet pairing under high field is predicted by bosonization.Comment: 18 pages, 19 figure
Scaling of Information in Turbulence
We propose a new perspective on Turbulence using Information Theory. We
compute the entropy rate of a turbulent velocity signal and we particularly
focus on its dependence on the scale. We first report how the entropy rate is
able to describe the distribution of information amongst scales, and how one
can use it to isolate the injection, inertial and dissipative ranges, in
perfect agreement with the Batchelor model and with a fBM model. In a second
stage, we design a conditioning procedure in order to finely probe the
asymmetries in the statistics that are responsible for the energy cascade. Our
approach is very generic and can be applied to any multiscale complex system.Comment: in Europhysics Letters, 201
The distribution of the ratio of consecutive level spacings in random matrix ensembles
We derive expressions for the probability distribution of the ratio of two
consecutive level spacings for the classical ensembles of random matrices. This
ratio distribution was recently introduced to study spectral properties of
many-body problems, as, contrary to the standard level spacing distributions,
it does not depend on the local density of states. Our Wigner-like surmises are
shown to be very accurate when compared to numerics and exact calculations in
the large matrix size limit. Quantitative improvements are found through a
polynomial expansion. Examples from a quantum many-body lattice model and from
zeros of the Riemann zeta function are presented.Comment: 5 pages, 4 figure
Haldane charge conjecture in one-dimensional multicomponent fermionic cold atoms
A Haldane conjecture is revealed for spin-singlet charge modes in
2N-component fermionic cold atoms loaded into a one-dimensional optical
lattice. By means of a low-energy approach and DMRG calculations, we show the
emergence of gapless and gapped phases depending on the parity of for
attractive interactions at half-filling. The analogue of the Haldane phase of
the spin-1 Heisenberg chain is stabilized for N=2 with non-local string charge
correlation, and pseudo-spin 1/2 edge states. At the heart of this even-odd
behavior is the existence of a spin-singlet pseudo-spin operator which
governs the low-energy properties of the model for attractive interactions and
gives rise to the Haldane physics.Comment: 4 pages, 4 figure
Emergence of Quintet Superfluidity in the Chain of Partially Polarized Spin-3/2 Ultracold Atom
The system of ultracold atoms with hyperfine spin might be unstable
against the formation of quintet pairs if the interaction is attractive in the
quintet channel. We have investigated the behavior of correlation functions in
a model including only s-wave interactions at quarter filling by large-scale
density-matrix renormalization-group simulations. We show that the correlations
of quintet pairs become quasi-long-ranged, when the system is partially
polarized, leading to the emergence of various mixed superfluid phases in which
BCS-like pairs carrying different magnetic moment coexist.Comment: 4 pages, 4 figures; significantly rewritten compared to the first
versio
Competing orders in one-dimensional half-filled multicomponent fermionic cold atoms: The Haldane-charge conjecture
We investigate the nature of the Mott-insulating phases of half-filled
2N-component fermionic cold atoms loaded into a one-dimensional optical
lattice. By means of conformal field theory techniques and large-scale DMRG
calculations, we show that the phase diagram strongly depends on the parity of
. First, we single out charged, spin-singlet, degrees of freedom, that carry
a pseudo-spin allowing to formulate a Haldane conjecture: for
attractive interactions, we establish the emergence of Haldane insulating
phases when is even, whereas a metallic behavior is found when is odd.
We point out that the cases do \emph{not} have the generic properties
of each family. The metallic phase for odd and larger than 1 has a
quasi-long range singlet pairing ordering with an interesting edge-state
structure. Moreover, the properties of the Haldane insulating phases with even
further depend on the parity of N/2. In this respect, within the low-energy
approach, we argue that the Haldane phases with N/2 even are not topologically
protected but equivalent to a topologically trivial insulating phase and thus
confirm the recent conjecture put forward by Pollmann {\it et al.} [Pollmann
{\it et al.}, arXiv:0909.4059 (2009)].Comment: 25 pages, 20 figure
Self-Similar Anisotropic Texture Analysis: the Hyperbolic Wavelet Transform Contribution
Textures in images can often be well modeled using self-similar processes
while they may at the same time display anisotropy. The present contribution
thus aims at studying jointly selfsimilarity and anisotropy by focusing on a
specific classical class of Gaussian anisotropic selfsimilar processes. It will
first be shown that accurate joint estimates of the anisotropy and
selfsimilarity parameters are performed by replacing the standard 2D-discrete
wavelet transform by the hyperbolic wavelet transform, which permits the use of
different dilation factors along the horizontal and vertical axis. Defining
anisotropy requires a reference direction that needs not a priori match the
horizontal and vertical axes according to which the images are digitized, this
discrepancy defines a rotation angle. Second, we show that this rotation angle
can be jointly estimated. Third, a non parametric bootstrap based procedure is
described, that provides confidence interval in addition to the estimates
themselves and enables to construct an isotropy test procedure, that can be
applied to a single texture image. Fourth, the robustness and versatility of
the proposed analysis is illustrated by being applied to a large variety of
different isotropic and anisotropic self-similar fields. As an illustration, we
show that a true anisotropy built-in self-similarity can be disentangled from
an isotropic self-similarity to which an anisotropic trend has been
superimposed
Doped two-leg ladder with ring exchange
The effect of a ring exchange on doped two-leg ladders is investigated
combining exact diagonalization (ED) and density matrix renormalization group
(DMRG) computations. We focus on the nature and weights of the low energy
magnetic excitations and on superconducting pairing. The stability with respect
to this cyclic term of a remarkable resonant mode originating from a hole
pair-magnon bound state is examined. We also find that, near the zero-doping
critical point separating rung-singlet and dimerized phases, doping reopens a
spin gap.Comment: 5 pages, 7 figures, to appear in PR
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