5,881 research outputs found
Spatially-modulated Superfluid States in Fermionic Optical Ladder Systems with Repulsive Interactions
We investigate two-component ultracold fermionic atoms with repulsive
interactions trapped in an optical lattice with a ladder structure. By applying
the Bogoliubov-de Gennes equations to an effective t-J model in the strong
correlation limit, we discuss how the spatially-modulated spin-singlet pairs
with d-wave like symmetry are formed in the systems with trapping potentials.
Furthermore, a close examination of the condensation energy as well as the
local average of potential, kinetic and exchange energies by means of the
variational Monte Carlo method elucidates that local particle correlations
enhance the stability of the superfluid state via substantial energy gain due
to singlet pairing in the high particle density region.Comment: 8 pages, 5 figure
Correlated electron transport through double quantum dots coupled to normal and superconducting leads
We study Andreev transport through double quantum dots connected in series
normal and superconducting (SC) leads, using the numerical renormalization
group. The ground state of this system shows a crossover between a local
Cooper-pairing singlet state and a Kondo singlet state, which is caused by the
competition between the Coulomb interaction and the SC proximity. We show that
the ground-state properties reflect this crossover especially for small values
of the inter-dot coupling , while in the opposite case, for large ,
another singlet with an inter-dot character becomes dominant. We find that the
conductance for the local SC singlet state has a peak with the unitary-limit
value . In contrast, the Andreev reflection is suppressed in the Kondo
regime by the Coulomb interaction. Furthermore, the conductance has two
successive peaks in the transient region of the crossover. It is further
elucidated that the gate voltage gives a different variation into the
crossover. Specifically, as the energy level of the dot that is coupled to the
normal lead varies, the Kondo screening cloud is deformed to a long-range
singlet bond.Comment: 11 pages, 10 figure
Ferromagnetism of cold fermions loaded into a decorated square lattice
We investigate two-component ultracold fermions loaded into a decorated
square lattice, which are described by the Hubbard model with repulsive
interactions and nearest neighbor hoppings. By combining the real-space
dynamical mean-field theory with the numerical renormalization group method, we
discuss how a ferromagnetically ordered ground state in the weak coupling
regime, which originates from the existence of a dispersionless band, is
adiabatically connected to a Heisenberg ferrimagnetic state in the strong
coupling limit. The effects of level splitting and hopping imbalance are also
addressed.Comment: 8 pages, 7 figure
Entropy and Barrier-Hopping Determine Conformational Viscoelasticity in Single Biomolecules
Biological macromolecules have complex and non-trivial energy landscapes,
endowing them a unique conformational adaptability and diversity in function.
Hence, understanding the processes of elasticity and dissipation at the
nanoscale is important to molecular biology and also emerging fields such as
nanotechnology. Here we analyse single molecule fluctuations in an atomic force
microscope (AFM) experiment using a generic model of biopolymer viscoelasticity
that importantly includes sources of local `internal' conformational
dissipation. Comparing two biopolymers, dextran and cellulose, polysaccharides
with and without the well-known `chair-to-boat' transition, reveals a signature
of this simple conformational change as minima in both the elasticity and
internal friction around a characteristic force. A calculation of two-state
populations dynamics offers a simple explanation in terms of an elasticity
driven by the entropy, and friction by barrier-controlled hopping, of
populations on a landscape. The microscopic model, allows quantitative mapping
of features of the energy landscape, revealing unexpectedly slow dynamics,
suggestive of an underlying roughness to the free energy.Comment: 25 pages, 7 figures, naturemag.bst, modified nature.cls
(naturemodified.cls
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Solutions to the Multi-Component 1/R Hubbard Model
In this work we introduce one dimensional multi-component Hubbard model of
1/r hopping and U on-site energy. The wavefunctions, the spectrum and the
thermodynamics are studied for this model in the strong interaction limit
. In this limit, the system is a special example of Luttinger
liquids, exhibiting spin-charge separation in the full Hilbert space.
Speculations on the physical properties of the model at finite on-site energy
are also discussed.Comment: 9 pages, revtex, Princeton-May1
Half-Quantum Vortices in Thin Film of Superfluid He
Stability of a half-quantum vortex (HQV) in superfluid He has been
discussed recently by Kawakami, Tsutsumi and Machida in Phys. Rev. B {\bf 79},
092506 (2009). We further extend this work here and consider the A phase of
superfluid He confined in thin slab geometry and analyze the HQV realized
in this setting. Solutions of HQV and singly quantized singular vortex are
evaluated numerically by solving the Ginzburg-Landau (GL) equation and
respective first critical angular velocities are obtained by employing these
solutions. We show that the HQV in the A phase is stable near the boundary
between the A and A phases. It is found that temperature and magnetic
field must be fixed first in the stable region and subsequently the angular
velocity of the system should be increased from zero to a sufficiently large
value to create a HQV with sufficiently large probability. A HQV does not form
if the system starts with a fixed angular velocity and subsequently the
temperature is lowered down to the A phase. It is estimated that the
external magnetic field with strength on the order of 1 T is required to have a
sufficiently large domain in the temperature-magnetic field phase diagram to
have a stable HQV.Comment: 5 pages, 5 figure
Renormalized Harmonic-Oscillator Description of Confined Electron Systems with Inverse-Square Interaction
An integrable model for SU() electrons with inverse-square interaction
is studied for the system with confining harmonic potential. We develop a new
description of the spectrum based on the {\it renormalized
harmonic-oscillators} which incorporate interaction effects via the repulsion
of energy levels. This approach enables a systematic treatment of the
excitation spectrum as well as the ground-state quantities.Comment: RevTex, 7 page
Supersolid state in fermionic optical lattice systems
We study ultracold fermionic atoms trapped in an optical lattice with
harmonic confinement by combining the real-space dynamical mean-field theory
with a two-site impurity solver. By calculating the local particle density and
the pair potential in the systems with different clusters, we discuss the
stability of a supersolid state, where an s-wave superfluid coexists with a
density-wave state of checkerboard pattern. It is clarified that a confining
potential plays an essential role in stabilizing the supersolid state. The
phase diagrams are obtained for several effective particle densities.Comment: 7 pages, 5 figures, Phys. Rev. A in pres
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