69 research outputs found
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
Exact low temperature results for transport properties of the interacting resonant level model
Using conformal field theory and integrability ideas, we give a full
characterization of the low temperature regime of the anisotropic interacting
resonant level (IRLM) model. We determine the low temperature corrections to
the linear conductance exactly up to the 6th order. We show that the structure
displays 'Coulomb deblocking' at resonance, i.e., a strong impurity-wire
capacitive coupling enhances the conductance at low temperature.Comment: 4 pages, 2 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
Reward circuitry is perturbed in the absence of the serotonin transporter
The serotonin transporter (SERT) modulates the entire serotonergic system in the brain and influences both the dopaminergic and norepinephrinergic systems. These three systems are intimately involved in normal physiological functioning of the brain and implicated in numerous pathological conditions. Here we use high-resolution magnetic resonance imaging (MRI) and spectroscopy to elucidate the effects of disruption of the serotonin transporter in an animal model system: the SERT knock-out mouse. Employing manganese-enhanced MRI, we injected Mn^(2+) into the prefrontal cortex and obtained 3D MR images at specific time points in cohorts of SERT and normal mice. Statistical analysis of co-registered datasets demonstrated that active circuitry originating in the prefrontal cortex in the SERT knock-out is dramatically altered, with a bias towards more posterior areas (substantia nigra, ventral tegmental area, and Raphé nuclei) directly involved in the reward circuit. Injection site and tracing were confirmed with traditional track tracers by optical microscopy. In contrast, metabolite levels were essentially normal in the SERT knock-out by in vivo magnetic resonance spectroscopy and little or no anatomical differences between SERT knock-out and normal mice were detected by MRI. These findings point to modulation of the limbic cortical–ventral striatopallidal by disruption of SERT function. Thus, molecular disruptions of SERT that produce behavioral changes also alter the functional anatomy of the reward circuitry in which all the monoamine systems are involved
Confinement and Superfluidity in one-dimensional Degenerate Fermionic Cold Atoms
The physical properties of arbitrary half-integer spins
fermionic cold atoms trapped in a one-dimensional optical lattice are
investigated by means of a low-energy approach. Two different superfluid phases
are found for depending on whether a discrete symmetry is
spontaneously broken or not: an unconfined BCS pairing phase and a confined
molecular superfluid instability made of fermions. We propose an
experimental distinction between these phases for a gas trapped in an annular
geometry. The confined-unconfined transition is shown to belong to the
generalized Ising universality class. We discuss on the possible Mott phases at
filling.Comment: 4 pages, revised versio
Shot noise in the self-dual Interacting Resonant Level Model
By using two independent and complementary approaches, we compute exactly the
shot noise in an out-of-equilibrium interacting impurity model, the Interacting
Resonant Level model at its self-dual point. An analytical approach based on
the Thermodynamical Bethe Ansatz allows to obtain the density matrix in the
presence of a bias voltage, which in turn allows for the computation of any
observable. A time-dependent Density Matrix Renormalization Group technique,
that has proven to yield the correct result for a free model (the Resonant
Level Model) is shown to be in perfect agreement with the former method.Comment: 4 pages, 3 figure
Dynamical Symmetry Enlargement Versus Spin-Charge Decoupling in the One-Dimensional SU(4) Hubbard Model
We investigate dynamical symmetry enlargement in the half-filled SU(4)
Hubbard chain using non-perturbative renormalization group and Quantum Monte
Carlo techniques. A spectral gap is shown to open for arbitrary Coulombic
repulsion . At weak coupling, , a SO(8) symmetry between
charge and spin-orbital excitations is found to be dynamically enlarged at low
energy. At strong coupling, , the charge degrees of freedom
dynamically decouple and the resulting effective theory in the spin-orbital
sector is that of the SO(6) antiferromagnetic Heisenberg model. Both regimes
exhibit spin-Peierls order. However, although spin-orbital excitations are
in the SO(6) regime they are in the SO(8) one. The
cross-over between these regimes is discussed.Comment: 4 pages, 2 figure
Heat transport of clean spin-ladders coupled to phonons: Umklapp scattering and drag
We study the low-temperature heat transport in clean two-leg spin ladder
compounds coupled to three-dimensional phonons. We argue that the very large
heat conductivities observed in such systems can be traced back to the
existence of approximate symmetries and corresponding weakly violated
conservation laws of the effective (gapful) low--energy model, namely
pseudo-momenta. Depending on the ratios of spin gaps and Debye energy and on
the temperature, the magnetic contribution to the heat conductivity can be
positive or negative, and exhibit an activated or anti-activated behavior. In
most regimes, the magnetic heat conductivity is dominated by the spin-phonon
drag: the excitations of the two subsystems have almost the same drift
velocity, and this allows for an estimate of the ratio of the magnetic and
phononic contributions to the heat conductivity.Comment: revised version, 8 pages, 3 figures, added appendi
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
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