Searcharxiv⌕ Search

arXiv subjects

G. Seibold

Publications and source records attributed to G. Seibold.

At least 73 records · Page 4Linked to original sources
arXiv2008

Slave-boson based configuration-interaction approach for the Hubbard model

Based on the Kotliar-Ruckenstein slave-boson scheme we develop a configuration-interaction (CI) approach which is suitable to improve the energy of symmetry-broken saddle-point solutions. The theory is applied to spin-polaron states in the Hubbard model and compared with analogous results obtained within the Hartree-Fock approximation. In addition we show that within the infinite ${\cal D}$ prescription of the Gutzwiller method a CI approach does not improve the variational result since in the thermodynamic limit matrix elements between different inhomogeneous states vanish due to an 'orthogonality catastrophe'.

cond-mat.str-el↗
arXiv2007

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.

cond-mat.str-el↗
arXiv2007

Intermediate scale phenomena in cuprates

After 20 years of research the low energy physics of cuprates remains a mystery. It is generally accepted that a three band Hamiltonian with Cu's and O's orbitals should contain the essential physics so we can say that there is consensus at the length scale of the Cu-O distance but there is disagreement when it comes to describe higher length scales or to set up a low energy model. Here we present computations of cuprates which accurately describe the physics arising at scales of up to several lattice constants. We review the comparison of our results with different proves as resonant X-ray scattering, scanning tunneling microscopy, optical conductivity and magnetic neutron scattering.

cond-mat.str-el↗
arXiv2006

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.

cond-mat.str-el↗
arXiv2006

Unified description of charge and spin excitations of stripes in cuprates

We study stripes in cuprates within the one-band and the three-band Hubbard model. Magnetic and charge excitations are described within the time-dependent Gutzwiller approximation. A variety of experiments (charge profile from resonant soft X-ray scattering, incommensurability vs. doping, optical excitations, magnetic excitations, etc.) are described within the same approach.

cond-mat.supr-con↗
arXiv2006

Checkerboard and stripe inhomogeneities in cuprates

We systematically investigate charge-ordering phases by means of a restricted and unrestricted Gutzwiller approximation to the single-band Hubbard model with nearest ($t$) and next-nearest neighbor hopping ($t'$). When $|t'/t|$ is small, as appropriate for ${\rm La_{2-x}Sr_xCuO_4}$, stripes are found, whereas in compounds with larger $|t'/t|$ (such as ${\rm Ca_{2-x}Na_x CuO_2Cl_2}$ and ${\rm Bi_2Sr_2CaCu_2O_{8+δ}}$) checkerboard structures are favored. In contrast to the linear doping dependence found for stripes the charge periodicity of checkerboard textures is locked to 4 unit cells over a wide doping range. In addition we find that checkerboard structures are favored at surfaces.

cond-mat.str-el↗
arXiv2006

Doping dependence of spin excitations in the stripe phase of high-Tc superconductors

Based on the time-dependent Gutzwiller approximation for the extended Hubbard model we calculate the energy and momentum dependence of spin excitations for striped ground states. Our starting point correctly reproduces the observed doping dependence of the incommensurability in La-based cuprates and the dispersion of magnetic modes in the insulating parent compound. This allows us to make quantitative predictions for the doping evolution of the dispersion of magnetic modes in the stripe phase including the energy and intensity of the resonance peak as well as the velocity of the spin-wave like Goldstone mode. In the underdoped regime $n_h<1/8$ we find a weak linear dependence of $ω_{res}$ on doping whereas the resonance energy significantly shifts to higher values when the charge concentration in the stripes starts to deviate from half-filling for $n_h>1/8$. The velocity $c$ is non-monotonous with a minimum at 1/8 in coincidence with a well known anomaly in $T_c$. Our calculations are in good agreement with available experimental data. We also compare our results with analogous computations based on linear spin-wave theory.

cond-mat.str-el↗
arXiv2005

Where is the spectral weight in magnetic neutron scattering in the cuprates?

We present estimates in the Hubbard and Heisenberg models for the spectral weight in magnetic neutron scattering experiments on the cuprates. With the aid of spin-wave theory and the time dependent Gutzwiller approximation we discuss how the spectral weight is distributed among the different channels and between high and low energies. In addition to the well known total moment sum rule we discuss sum rules for each component of the dynamical structure factor tensor which are peculiar for spin 1/2 systems. The various factors that reduce the spectral weight at the relevant energies are singled out and analyzed like: shielding factors, weight at electronic energies, multimagnon process etc. Although about 10% ~ 15% of the naively expected weight is detected in experiments after consideration of these factors the missing weight is within the experimental uncertainties. A large fraction of the spectral weight is hard to detect with present experimental conditions.

cond-mat.str-el↗
arXiv2004

Theory of isotope effect in photoemission spectra of high-T_c superconducting cuprates

We investigate the effect of isotope substitution on the electronic spectral functions within a model where the charge carriers are coupled to bosonic charge-order (CO) fluctuations centered around some mean frequency ω_0 and with enhanced scattering at wave-vector q_c. It is shown that a mass dependence of ω_0 is not sufficient in order to account, especially at high energies, for the dispersion shifts experimentally observed in an optimally doped superconducting cuprate. We argue that isotope substitution induces a change of the spatial CO correlations which gives good account of the experimental data.

cond-mat.supr-con↗
arXiv2004

Magnetic fluctuations from stripes in cuprates

Within the time-dependent Gutzwiller approximation for the Hubbard model we compute the magnetic fluctuations of vertical metallic stripes with parameters appropriate for La$_{1.875}$Ba$_{0.125}$CuO$_4$ (LBCO). For bond- and site-centered stripes the excitation spectra are similar, consisting of a low-energy incommensurate acoustic branch which merges into a ``resonance peak'' at the antiferromagnetic wave vector and several high-energy optical branches. The acoustic branch is similar to the result of theories assuming localized spins whereas the optical branches are significantly different. Results are in good agreement with a recent inelastic neutron study of LBCO.

cond-mat.str-el↗
arXiv2003

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.

cond-mat.str-el↗
arXiv2003

Stability of metallic stripes in the extended one-band Hubbard model

Based on an unrestricted Gutzwiller approximation (GA) we investigate the stripe orientation and periodicity in an extended one-band Hubbard model. A negative ratio between next-nearest and nearest neighbor hopping t'/t, as appropriate for cuprates, favors partially filled (metallic) stripes for both vertical and diagonal configurations. At around optimal doping diagonal stripes, site centered (SC) and bond centered (BC) vertical stripes become degenerate suggesting strong lateral and orientational fluctuations. We find that within the GA the resulting phase diagram is in agreement with experiment whereas it is not in the Hartree-Fock approximation due to a strong overestimation of the stripe filling. Results are in agreement with previous calculations within the three-band Hubbard model but with the role of SC and BC stripes interchanged.

cond-mat.str-el↗
arXiv2003

Charge instabilities in strongly correlated bilayer systems

We investigate the charge-instabilities of the Hubbard-Holstein model with two coupled layers. In this system the scattering processes naturally separate into contributions which are either symmetric or antisymmetric combinations with respect to exchange of the layers. It turns out that the short-range strong correlations suppress finite wave-vector nesting instabilities for both symmetries but favor the occurrence of phase separation in the symmetric channel. Inclusion of a sizeable long-range Coulomb (LRC) interaction frustrates the q=0 instabilities and supports the formation of incommensurate charge-density waves (CDW). Upon reducing doping from half-filling and for small electron-phonon coupling g the CDW instability first occurs in the antisymmetric channel but both instability lines merge with increasing g. While LRC forces always suppress the phase separation instability in the symmetric channel, the CDW period in the antisymmetric sector tends to infinity (q_c -> 0) for sufficiently small Coulomb interaction. This feature allows for the possibility of singular scattering over the whole Fermi surface. We discuss possible implications of our results for the bilayer high-Tc cuprates.

cond-mat.str-el↗
arXiv2003

Temperature dependence of the collective mode and its influence on the band splitting in bilayer cuprates

The recently observed bilayer splitting in high-T$_c$ cuprates is analyzed within a model where the charge carriers are coupled to a phenomenological bosonic spectrum which interpolates between the marginal Fermi liquid structure and collective mode type behavior as a function of temperature. We argue that the origin of the collective mode is probably associated with dynamic incommensurate charge density waves. Moreover it is shown that the resulting temperature dependence of the self-energy $Σ$ is in good agreement with $Σ$ as extracted from angle-resolved photoemission data.

cond-mat.supr-con↗
arXiv2002

Dynamics of metallic stripes in cuprates

We study the dynamics of metallic vertical stripes in cuprates within the three-band Hubbard model based on a recently developed time dependent Gutzwiller approximation. As doping increases the optical conductivity shows transfer of spectral weight from the charge transfer band towards i) an incoherent band centered at 1.3eV, {ii} a Drude peak, mainly due to motion along the stripe, {iii} a low energy collective mode which softens with doping and merges with ii} at optimum doping in good agreement with experiment. The softening is related to the quasidegeneracy between Cu centered and O centered mean-field stripe solutions close to optimal doping.

cond-mat.str-el↗
arXiv2002

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.

cond-mat.str-el↗
arXiv2002

Metallic mean-field stripes, incommensurability and chemical potential in cuprates

We perform a systematic slave-boson mean-field analysis of the three-band model for cuprates with first-principle parameters. Contrary to widespread believe based on earlier mean-field computations low doping stripes have a linear density close to 1/2 added hole per lattice constant. We find a dimensional crossover from 1D to 2D at doping $\sim 0.1$ followed by a breaking of particle-hole symmetry around doping 1/8 as doping increases. Our results explain in a simple way the behavior of the chemical potential, the magnetic incommensurability, and transport experiments as a function of doping. Bond centered and site-centered stripes become degenerate for small overdoping.

cond-mat.str-el↗