923 research outputs found
Breathers and Raman scattering in a two-leg ladder with staggered Dzialoshinskii-Moriya interaction
Recent experiments have revealed the role of staggered Dzialoshinskii-Moriya
interaction in the magnetized phase of an antiferromagnetic spin 1/2 two-leg
ladder compound under a uniform magnetic field. We derive a low energy
effective field theory describing a magnetized two-leg ladder with a weak
staggered Dzialoshinskii-Moriya interaction. This theory predicts the
persistence of the spin gap in the magnetized phase, in contrast to standard
two-leg ladders, and the presence of bound states in the excitation spectrum.
Such bound states are observable in Raman scattering measurements. These
results are then extended to intermediate Dzialoshinskii-Moriya interaction
using Exact Diagonalizations.Comment: RevTeX 4, 14 pages, 11 EPS figure
Competing orders in the generalized Hund chain model at half-filling
By using a combination of several non-perturbative techniques -- a
one-dimensional field theoretical approach together with numerical simulations
using density matrix renormalization group -- we present an extensive study of
the phase diagram of the generalized Hund model at half-filling. This model
encloses the physics of various strongly correlated one-dimensional systems,
such as two-leg electronic ladders, ultracold degenerate fermionic gases
carrying a large hyperfine spin 3/2, other cold gases like Ytterbium 171 or
alkaline-earth condensates. A particular emphasis is laid on the possibility to
enumerate and exhaust the eight possible Mott insulating phases by means of a
duality approach. We exhibit a one-to-one correspondence between these phases
and those of the two-leg Hubbard ladder with interchain hopping. Our results
obtained from a weak coupling analysis are in remarkable quantitative agreement
with our numerical results carried out at moderate coupling.Comment: 26 pages, 14 figure
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
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
Trionic and quartetting phases in one-dimensional multicomponent ultracold fermions
We investigate the possible formation of a molecular condensate, which might
be, for instance, the analogue of the alpha condensate of nuclear physics, in
the context of multicomponent cold atoms fermionic systems. A simple
paradigmatic model of N-component fermions with contact interactions loaded
into a one-dimensional optical lattice is studied by means of low-energy and
numerical approaches. For attractive interaction, a quasi-long-range molecular
superfluid phase, formed from bound-states made of N fermions, emerges at low
density. We show that trionic and quartetting phases, respectively for N=3,4,
extend in a large domain of the phase diagram and are robust against small
symmetry-breaking perturbations.Comment: Contribution to the SOTANCP 2008 worksho
Zeeman effect in superconducting two-leg ladders: irrational magnetization plateaus and exceeding the Pauli limit
The effect of a parallel magnetic field on superconducting two-leg ladders is
investigated numerically. The magnetization curve displays an irrational
plateau at a magnetization equal to the hole density. Remarkably, its stability
is fundamentally connected to the existence of a well-known magnetic resonant
mode. Once the zero-field spin gap is suppressed by the field, pairs acquire a
finite momentum characteristic of a Fulde-Ferrell-Larkin-Ovchinnikov phase. In
addition, S^z=0 triplet superconducting correlations coexist with singlet ones
above the irrational plateau. This provides a simple mechanism in which the
Pauli limit is exceeded as suggested by recent experiments.Comment: 4 pages, 6 figure
Recent progress in the truncated Lanczos method : application to hole-doped spin ladders
The truncated Lanczos method using a variational scheme based on Hilbert
space reduction as well as a local basis change is re-examined. The energy is
extrapolated as a power law function of the Hamiltonian variance. This
systematic extrapolation procedure is tested quantitatively on the two-leg t-J
ladder with two holes. For this purpose, we have carried out calculations of
the spin gap and of the pair dispersion up to size 2x15.Comment: 5 pages, 4 included eps figures, submitted to Phys. Rev. B; revised
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