933 research outputs found
Phase diagrams of voltage-gated oxide interfaces with strong Rashba coupling
We propose a model for the two-dimensional electron gas formed at the
interface of oxide heterostructures that includes a Rashba spin-orbit coupling
proportional to an electric field oriented perpendicularly to the interface.
Taking into account the electron density dependence of this electric field
confining the electron gas at the interface, we report the occurrence of a
phase separation instability (signaled by a negative compressibility) for
realistic values of the spin-orbit coupling and of the electronic
band-structure parameters at zero temperature. We extend the analysis to finite
temperatures and in the presence of an in-plane magnetic field, thereby
obtaining two phase diagrams which exhibit a phase separation dome. By varying
the gating potential the phase separation dome may shrink and vanish at zero
temperature into a quantum critical point where the charge fluctuates
dynamically. Similarly the phase separation may be spoiled by a planar magnetic
field even at zero temperature leading to a line of quantum critical points.Comment: 17 pages, 17 figure
Spectral properties of incommensurate charge-density wave systems
The concept of frustrated phase separation is applied to investigate its
consequences for the electronic structure of the high T_c cuprates. The
resulting incommensurate charge density wave (CDW) scattering is most effective
in creating local gaps in k-space when the scattering vector connects states
with equal energy. Starting from an open Fermi surface we find that the
resulting CDW is oriented along the (10)- and (or) (01)-direction which allows
for a purely one-dimensional or a two-dimensional ``eggbox type'' charge
modulation. In both cases the van Hove singularities are substantially
enhanced, and the spectral weight of Fermi surface states near the M-points,
tends to be suppressed. Remarkably, a leading edge gap arises near these
points, which, in the eggbox case, leaves finite arcs of the Fermi surface
gapless. We discuss our results with repect to possible consequences for
photoemission experiments
Theory of antibound states in partially filled narrow band systems
We present a theory of the dynamical two-particle response function in the
Hubbard model based on the time-dependent Gutzwiller approximation. The results
are in excellent agreement with exact diagonalization on small clusters and
give reliable results even for high densities, where the usual ladder
approximation breaks down. We apply the theory to the computation of antibound
states relevant for Auger spectroscopy and cold atom physics. A special bonus
of the theory is its computational simplicity.Comment: 4 pages, 3 figure
Time-dependent Gutzwiller theory of magnetic excitations in the Hubbard model
We use a spin-rotational invariant Gutzwiller energy functional to compute
random-phase-approximation-like (RPA) fluctuations on top of the Gutzwiller
approximation (GA). The method can be viewed as an extension of the previously
developed GA+RPA approach for the charge sector [G. Seibold and J. Lorenzana,
Phys. Rev. Lett. {\bf 86}, 2605 (2001)] with respect to the inclusion of the
magnetic excitations. Unlike the charge case, no assumptions about the time
evolution of the double occupancy are needed in this case. Interestingly, in a
spin-rotational invariant system, we find the correct degeneracy between
triplet excitations, showing the consistency of both computations. Since no
restrictions are imposed on the symmetry of the underlying saddle-point
solution, our approach is suitable for the evaluation of the magnetic
susceptibility and dynamical structure factor in strongly correlated
inhomogeneous systems. We present a detailed study of the quality of our
approach by comparing with exact diagonalization results and show its much
higher accuracy compared to the conventional Hartree-Fock+RPA theory. In
infinite dimensions, where the GA becomes exact for the Gutzwiller variational
energy, we evaluate ferromagnetic and antiferromagnetic instabilities from the
transverse magnetic susceptibility. The resulting phase diagram is in complete
agreement with previous variational computations.Comment: 12 pages, 8 figure
Possible mechanisms of electronic phase separation in oxide interfaces
LaAlO3/SrTiO3 ad LaTiO3/SrTiO3 interfaces are known to host a strongly
inhomogeneous (nearly) two-dimensional electron gas (2DEG). In this work we
present three unconventional electronic mechanisms of electronic phase
separation (EPS) in a 2DEG as a possible source of inhomogeneity in oxide
interfaces. Common to all three mechanisms is the dependence of some
(interaction) potential on the 2DEG's density. We first consider a mechanism
resulting from a sizable density-dependent Rashba spin-orbit coupling. Next, we
point out that an EPS may also occur in the case of a density-dependent
superconducting pairing interaction. Finally, we show that the confinement of
the 2DEG to the interface by a density-dependent, self-consistent electrostatic
potential can by itself cause an EPS.Comment: 4 pages and 4 figures, Proceedings of the International Conference
"Superstripes 2014", 25-31 July 2015, Erice, Ital
Inhomogeneous Gutzwiller approximation with random phase fluctuations for the Hubbard model
We present a detailed study of the time-dependent Gutzwiller approximation
for the Hubbard model. The formalism, labelled GA+RPA, allows us to compute
random-phase approximation-like (RPA) fluctuations on top of the Gutzwiller
approximation (GA). No restrictions are imposed on the charge and spin
configurations which makes the method suitable for the calculation of linear
excitations around symmetry-broken solutions. Well-behaved sum rules are obeyed
as in the Hartree-Fock (HF) plus RPA approach. Analytical results for a
two-site model and numerical results for charge-charge and current-current
dynamical correlation functions in one and two dimensions are compared with
exact and HF+RPA results, supporting the much better performance of GA+RPA with
respect to conventional HF+RPA theory.Comment: 14 pages, 6 figure
Quantum Lifshitz point in the infinite dimensional Hubbard model
We show that the Gutzwiller variational wave function is surprisingly
accurate for the computation of magnetic phase boundaries in the infinite
dimensional Hubbard model. This allows us to substantially extend known phase
diagrams. For both the half-hypercubic and the hypercubic lattice a large part
of the phase diagram is occupied by an incommensurate phase, intermediate
between the ferromagnetic and the paramagnetic phase. In case of the hypercubic
lattice the three phases join at a new quantum Lifshitz point at which the
order parameter is critical and the stiffness vanishes.Comment: 4 pages, 3 figure
Serum antibodies in first-degree relatives of patients with IBD: A marker of disease susceptibility? A follow-up pilot-study after 7 years
Introduction: Various disease-specific serum antibodies were described in patients with inflammatory bowel disease and their yet healthy first-degree relatives. In the latter, serum antibodies are commonly regarded as potential markers of disease susceptibility. The present long-term follow-up study evaluated the fate of antibody-positive first-degree relatives. Patients and Methods: 25 patients with Crohn's disease, 19 patients with ulcerative colitis and 102 first-degree relatives in whom presence of ASCA, pANCA, pancreatic- and goblet-cell antibodies had been assessed were enrolled. The number of incident cases with inflammatory bowel disease was compared between antibody-positive and antibody-negative first-degree relatives 7 years after storage of serum samples. Results: 34 of 102 (33%) first-degree relatives were positive for at least one of the studied serum antibodies. In the group of first-degree relatives, one case of Crohn's disease and one case of ulcerative colitis were diagnosed during the follow-up period. However, both relatives did not display any of the investigated serum antibodies (p = 1). Discussion: The findings of our pilot study argue against a role of serum antibodies as a marker of disease susceptibility in first-degree relatives of patients with inflammatory bowel disease. However, these data have to await confirmation in larger ideally prospective multicenter studies before definite conclusions can be drawn
Serum antibodies in first-degree relatives of patients with IBD: A marker of disease susceptibility? A follow-up pilot-study after 7 years
Introduction: Various disease-specific serum antibodies were described in patients with inflammatory bowel disease and their yet healthy first-degree relatives. In the latter, serum antibodies are commonly regarded as potential markers of disease susceptibility. The present long-term follow-up study evaluated the fate of antibody-positive first-degree relatives. Patients and Methods: 25 patients with Crohn's disease, 19 patients with ulcerative colitis and 102 first-degree relatives in whom presence of ASCA, pANCA, pancreatic- and goblet-cell antibodies had been assessed were enrolled. The number of incident cases with inflammatory bowel disease was compared between antibody-positive and antibody-negative first-degree relatives 7 years after storage of serum samples. Results: 34 of 102 (33%) first-degree relatives were positive for at least one of the studied serum antibodies. In the group of first-degree relatives, one case of Crohn's disease and one case of ulcerative colitis were diagnosed during the follow-up period. However, both relatives did not display any of the investigated serum antibodies (p = 1). Discussion: The findings of our pilot study argue against a role of serum antibodies as a marker of disease susceptibility in first-degree relatives of patients with inflammatory bowel disease. However, these data have to await confirmation in larger ideally prospective multicenter studies before definite conclusions can be drawn
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