1,312 research outputs found
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
On the reliability of electrical drives for safety-critical applications
The aim of this work is to present some issues related to fault tolerant electric drives,which are able to overcome different types of faults occurring in the sensors, in thepower converter and in the electrical machine, without compromising the overallfunctionality of the system. These features are of utmost importance in safety-criticalapplications. In this paper, the reliability of both commercial and innovative driveconfigurations, which use redundant hardware and suitable control algorithms, will beinvestigated for the most common types of fault: besides standard three phase motordrives, also multiphase topologies, open-end winding solutions, multi-machineconfigurations will be analyzed, applied to various electric motor technologies. Thecomplexity of hardware and control strategies will also be compared in this paper, sincethis has a tremendous impact on the investment costs
A High-Efficiency, Low-Cost Solution for On-Board Power Converters
Wide-input, low-voltage, and high-current applications are addressed. A single-ended isolated topology which improves the power efficiency, reduces both switching and conduction losses, and heavily lowers the system cost is presented. During each switching cycle, the transformer core reset is provided. The traditional tradeoff between the maximum allowable duty-cycle and the reset voltage is avoided and the off-voltage of active switches is clamped to the input voltage. Therefore, the system cost is heavily reduced and the converter is well suited for wide-input applications. Zero-voltage switching is achieved for active switches, and the power efficiency is greatly improved. In the output mesh, an inductor is included making the converter suitable for high-current, low-voltage applications. Since the active clamp forward converter is the closest competitor of the proposed converter, a comparison is provided as well. In this paper, the steady-state and small-signal analysis of the proposed converter is presented. Design examples are provided for further applications. Simulation and experimental results are shown to validate the great advantages brought by the proposed topology
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
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
Semiclassical Approach to Competing Orders in Two-leg Spin Ladder with Ring-Exchange
We investigate the competition between different orders in the two-leg spin
ladder with a ring-exchange interaction by means of a bosonic approach. The
latter is defined in terms of spin-1 hardcore bosons which treat the N\'eel and
vector chirality order parameters on an equal footing. A semiclassical approach
of the resulting model describes the phases of the two-leg spin ladder with a
ring-exchange. In particular, we derive the low-energy effective actions which
govern the physical properties of the rung-singlet and dominant vector
chirality phases. As a by-product of our approach, we reveal the mutual
induction phenomenon between spin and chirality with, for instance, the
emergence of a vector-chirality phase from the application of a magnetic field
in bilayer systems coupled by four-spin exchange interactions.Comment: 15 pages, 9 figure
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
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