12 research outputs found
Triplet superconductivity in a 1D itinerant electron system with transverse spin anisotropy
In this paper we study the ground state phase diagram of a one-dimensional
t-J-U model away from half-filling. In the large-bandwidth limit and for
ferromagnetic exchange with easy-plane anisotropy a phase with gapless charge
and massive spin excitations, characterized by the coexistence of triplet
superconducting and spin density wave instabilities is realized in the ground
state. With increasing ferromagnetic exchange transitions into a ferrometallic
and then a spin gapped triplet superconducting phase take place.Comment: 11 pages, 10 figures, accepted for publication in Eur. Phys. J.
Generalized hole-particle transformations and spin reflection positivity in multi-orbital systems
We propose a scheme combining spin reflection positivity and generalized
hole-particle and orbital transformations to characterize the symmetry
properties of the ground state for some correlated electron models on bipartite
lattices. In particular, we rigorously determine at half-filling and for
different regions of the parameter space the spin, orbital and pairing
pseudospin of the ground state of generalized two-orbital Hubbard models which
include the Hund's rule coupling.Comment: 6 pages, 2 figure
Stripe Ansatzs from Exactly Solved Models
Using the Boltzmann weights of classical Statistical Mechanics vertex models
we define a new class of Tensor Product Ansatzs for 2D quantum lattice systems,
characterized by a strong anisotropy, which gives rise to stripe like
structures. In the case of the six vertex model we compute exactly, in the
thermodynamic limit, the norm of the ansatz and other observables. Employing
this ansatz we study the phase diagram of a Hamiltonian given by the sum of XXZ
Hamiltonians along the legs coupled by an Ising term. Finally, we suggest a
connection between the six and eight-vertex Anisotropic Tensor Product Ansatzs,
and their associated Hamiltonians, with the smectic stripe phases recently
discussed in the literature.Comment: REVTEX4.b4 file, 10 pages, 2 ps Figures. Revised version to appear in
PR
Optimum ground states of generalized Hubbard models with next-nearest neighbour interaction
We investigate the stability domains of ground states of
generalized Hubbard models with next-nearest neighbour
interaction using the optimum groundstate approach. We focus on
the η-pairing state with momentum P=0 and the fully polarized
ferromagnetic state at half-filling. For these states exact lower bounds
for the regions of stability are obtained in the form of
inequalities between the interaction parameters.
For the model with only nearest neighbour interaction we show that
the bounds for the stability regions can be improved by considering
larger clusters. Additional next-nearest neighbour interactions
can lead to larger or smaller stability regions depending on the
parameter values
Triplet superconductivity vs. easy-plane ferromagnetism in a 1D itinerant electron system with transverse spin anisotropy
In this paper we study the ground state phase diagram of a
one-dimensional model, at half-filling. In the large-bandwidth
limit and for ferromagnetic exchange with easy-plane anisotropy, a phase
with gapless charge and massive spin excitations, characterized by the
coexistence of triplet superconducting and spin density wave
instabilities is realized in the ground state. With reduction
of the bandwidth, a transition into an insulating phase showing properties
of the spin- XY model takes place