137 research outputs found
Cooper-pair transport through a Hubbard chain sandwiched between two superconductors: Density matrix renormalization group calculations
We present a numerical approach to study the coherent transport of Cooper
pairs through a Hubbard chain, and study the role of the contacts in achieving
perfect Andreev reflection. We calculate the pair transport using the Density
Matrix Renormalization Group by measuring the response of the system to quantum
pair fields with complex phases on the two ends of an open system. This
approach gives an effective superfluid weight which is in close agreement with
the Bethe Ansatz results for the superfluid weight for closed Hubbard rings.Comment: 5 pages, 6 figure
Probing the pairing symmetry and pair charge stiffness of doped ladders
We perform the numerical equivalent of a phase sensitive experiment on doped
ladders. We apply proximity effect fields with different complex phases
at both ends of an open system and we study the transport of Cooper pairs.
Measuring the response of the system and the induced Josephson current, Density
Matrix Renormalization Group calculations show how, depending on the doping
fraction, the rung-leg parity of the pair field changes from minus to plus as
the density of holes is increased. We also study the pair charge stiffness, and
we observe a supression of the superconductivity in the region where static
stripes appear. We compare our results with predictions from bosonization and
renormalization group analysis.Comment: 4 pages, 5 figure
Topological Confinement and Superconductivity
We derive a Kondo Lattice model with a correlated conduction band from a
two-band Hubbard Hamiltonian. This mapping allows us to describe the emergence
of a robust pairing mechanism in a model that only contains repulsive
interactions. The mechanism is due to topological confinement and results from
the interplay between antiferromagnetism and delocalization. By using
Density-Matrix-Renormalization-Group (DMRG), we demonstrate that this mechanism
leads to dominant superconducting correlations in a 1D-system.Comment: 4 pages, 4 figure
Three-dimensional Gross-Pitaevskii solitary waves in optical lattices: stabilization using the artificial quartic kinetic energy induced by lattice shaking
In this Letter, we show that a three-dimensional Bose-Einstein solitary wave
can become stable if the dispersion law is changed from quadratic to quartic.
We suggest a way to realize the quartic dispersion, using shaken optical
lattices. Estimates show that the resulting solitary waves can occupy as little
as -th of the Brillouin zone in each of the three directions and
contain as many as atoms, thus representing a \textit{fully
mobile} macroscopic three-dimensional object.Comment: 8 pages, 1 figure, accepted in Phys. Lett.
A study of long range order in certain two-dimensional frustrated lattices
We have studied the Heisenberg antiferromagnets on two-dimensional frustrated
lattices, triangular and kagome lattices using linear spin-wave theory. A
collinear ground state ordering is possible if one of the three bonds in each
triangular plaquette of the lattice becomes weaker or frustrated. We study
spiral order in the Heisenberg model along with Dzyaloshinskii-Moriya (DM)
interaction and in the presence of a magnetic field. The quantum corrections to
the ground state energy and sublattice magnetization are calculated
analytically in the case of triangular lattice with nearesr-neighbour
interaction. The corrections depend on the DM interaction strength and the
magnetic field. We find that the DM interaction stabilizes the long-range
order, reducing the effect of quantum fluctuations. Similar conclusions are
reached for the kagome lattice. We work out the linear spin-wave theory at
first with only nearest-neighbour (nn) terms for the kagome lattice. We find
that the nn interaction is not sufficient to remove the effects of low energy
fluctuations. The flat branch in the excitation spectrum becomes dispersive on
addition of furthet neighbour interactions. The ground state energy and the
excitation spectrum have been obtained for various cases.Comment: 18 pages, 9 figure
Quasi-Fermi liquid behavior in a one-dimensional system of interacting spinless fermions
We present numerical evidence for a new paradigm in one-dimensional
interacting fermion systems, whose phenomenology has traits of both, Luttinger
liquids and Fermi liquids. This new state, dubbed a quasi-Fermi liquid,
possesses a discontinuity in its fermion occupation number at the Fermi
momentum. The excitation spectrum presents particle-like quasiparticles, and
absence of hole-like quasiparticles, giving rise instead to edge singularities.
Such a state is realized in a one-dimensional spinless fermion lattice
Hamiltonian by fine-tuning the interactions to a regime where they become
irrelevant in the renormalization group sense. We show, using uniform infinite
matrix products states and finite-entanglement scaling analysis, that the
system ground state is characterized by a Luttinger parameter and a
discontinuous jump in the fermion occupation number. We support the
characterization with calculations of the spectral function, that show a
particle-hole asymmetry reflected in the existence of well-defined Landau
quasiparticles above the Fermi level, and edge singularities without the
associated quasiparticles below. These results indicate that the quasi-Fermi
liquid paradigm can be realized beyond the low-energy perturbative realm.Comment: 9+3 pages; 8+4 figure
- …