190 research outputs found
Pairing states of a polarized Fermi gas trapped in a one-dimensional optical lattice
We study the properties of a one-dimensional (1D) gas of fermions trapped in
a lattice by means of the density matrix renormalization group method, focusing
on the case of unequal spin populations, and strong attractive interaction. In
the low density regime, the system phase-separates into a well defined
superconducting core and a fully polarized metallic cloud surrounding it. We
argue that the superconducting phase corresponds to a 1D analogue of the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, with a quasi-condensate of
tightly bound bosonic pairs with a finite center-of-mass momentum that scales
linearly with the magnetization. In the large density limit, the system allows
for four phases: in the core, we either find a Fock state of localized pairs or
a metallic shell with free spin-down fermions moving in a fully filled
background of spin-up fermions. As the magnetization increases, the Fock state
disappears to give room for a metallic phase, with a partially polarized
superconducting FFLO shell and a fully polarized metallic cloud surrounding the
core.Comment: 4 pages, 5 fig
Functional screening in Drosophila reveals the conserved role of REEP1 in promoting stress resistance and preventing the formation of Tau aggregates
Pathological modifications in the microtubule-associated protein Tau is a common characteristic observed in different neurological diseases, suggesting that analogous metabolic pathways might be similarly affected during neurodegeneration. To identify these molecules and mechanisms, we utilized Drosophila models of human Tau-mediated neurodegeneration to perform an RNA interference functional screening against genes considered to be implicated in the pathogenesis of different neurodegenerative disorders. We found that the downregulation of the Drosophila REEP1 homolog protein enhanced Tau toxicity with increased formation of insoluble aggregates. On the contrary, the overexpression of either the Drosophila or the human REEP1 protein was able to revert these phenotypes and promote neuronal resistance to ER stress. These studies identify a new function for the REEP1 protein in vivo and a novel cellular mechanism to prevent Tau toxicity
Spectral properties of a partially spin-polarized one-dimensional Hubbard/Luttinger superfluid
We calculate the excitation spectra of a spin-polarized Hubbard chain away
from half-filling, using a high-precision momentum-resolved time-dependent
Density Matrix Renormalization Group method. Focusing on the U<0 case, we
present in some detail the single-fermion, pair, density and spin spectra, and
discuss how spin-charge separation is altered for this system. The pair spectra
show a quasi-condensate at a nonzero momentum proportional to the polarization,
as expected for this Fulde-Ferrel-Larkin-Ovchinnikov-like superfluid.Comment: 4 pages, 3 low resolution color fig
Pair correlations of a spin-imbalanced Fermi gas on two-leg ladders
We study the pair correlations of a spin-imbalanced two-leg ladder with
attractive interactions, using the density matrix renormalization group method
(DMRG). We identify regions in the phase diagram spanned by the chemical
potential and the magnetic field that can harbor
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-like physics. Results for the pair
structure factor, exhibiting multiple pairing wave-vectors, substantiate the
presence of FFLO-like correlations. We further discuss phase separation
scenarios induced by a harmonic trap, which differ from the case of isolated
chains.Comment: To appear in Phys. Rev. Lett.; minor revision
Non-equilibrium electronic transport in a one-dimensional Mott insulator
We calculate the non-equilibrium electronic transport properties of a
one-dimensional interacting chain at half filling, coupled to non-interacting
leads. The interacting chain is initially in a Mott insulator state that is
driven out of equilibrium by applying a strong bias voltage between the leads.
For bias voltages above a certain threshold we observe the breakdown of the
Mott insulator state and the establishment of a steady-state electronic current
through the system. Based on extensive time-dependent density matrix
renormalization group simulations, we show that this steady-state current
always has the same functional dependence on voltage, independent of the
microscopic details of the model and relate the value of the threshold to the
Lieb-Wu gap. We frame our results in terms of the Landau-Zener dielectric
breakdown picture. Finally, we also discuss the real-time evolution of the
current, and characterize the current-carrying state resulting from the
breakdown of the Mott insulator by computing the double occupancy, the spin
structure factor, and the entanglement entropy.Comment: 12 pages RevTex4, 12 eps figures, as published, minor revision
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