Landau mapping and Fermi liquid parameters of the 2D t-J model

We study the momentum distribution function n(k) in the 2D t-J model on small clusters by exact diagonalization. We show that n(k) can be decomposed systematically into two components with Bosonic and Fermionic doping dependence. The Bosonic component originates from the incoherent motion of holes and has no significance for the low energy physics. For the Fermionic component we exlicitely perform the one-to-one Landau mapping between the low lying eigenstates of the t-J model clusters and those of an equivalent system of spin-1/2 quasiparticles. This mapping allows to extract the quasiparticle dispersion, statistics, and Landau parameters. The results show conclusively that the 2D t-J model for small doping is a Fermi liquid with a `small' Fermi surface and a moderately strong attractive interaction between the quasiparticles.Comment: Revtex file, 5 pages with 5 embedded eps-files, hardcopies of figures (or the entire manuscript) can be obtained by e-mail request to: [email protected]

Anomalous Spin and Charge Dynamics of the 2D t-J Model at low doping

We present an exact diagonalization study of the dynamical spin and density correlation function of the 2D t-J model for hole doping < 25%. Both correlation functions show a remarkably regular, but completely different scaling behaviour with both hole concentration and parameter values: the density correlation function is consistent with that of bosons corresponding to the doped holes and condensed into the lowest state of the noninteracting band of width 8t, the spin correlation function is consistent with Fermions in a band of width J. We show that the spin bag picture gives a natural explanation for this unusual behaviour.Comment: Revtex-file, 4 PRB pages + 5 figures attached as uu-encoded ps-files Hardcopies of figures (or the entire manuscript) can also be obtained by e-mailing to: [email protected]

First Experiences Integrating PC Distributed I/O Into Argonne's ATLAS Control System

First Experiences Integrating PC Distributed I/O Into Argonne's ATLAS Control System The roots of ATLAS (Argonne Tandem-Linac Accelerator System) date back to the early 1960s. Located at the Argonne National Laboratory, the accelerator has been designated a National User Facility, which focuses primarily on heavy-ion nuclear physics. Like the accelerator it services, the control system has been in a constant state of evolution. The present real-time portion of the control system is based on the commercial product Vsystem [1]. While Vsystem has always been capable of distributed I/O processing, the latest offering of this product provides for the use of relatively inexpensive PC hardware and software. This paper reviews the status of the ATLAS control system, and describes first experiences with PC distributed I/O.Comment: ICALEPCS 2001 Conference, PSN WEAP027, 3 pages, 1 figur

Quasiparticle dispersion of the t-J and Hubbard models

The spectral weight ${\rm A({\bf p},\omega)}$ of the two dimensional ${\rm t-J}$ and Hubbard models has been calculated using exact diagonalization and quantum Monte Carlo techniques, at several densities ${\rm 1.0 \leq \langle n \rangle \leq 0.5}$. The photoemission $(\omega < 0)$ region contains two dominant distinct features, namely a low-energy quasiparticle peak with bandwidth of order J, and a broad valence band peak at energies of order t. This behavior $persists$ away from half-filling, as long as the antiferromagnetic (AF) correlations are robust. The results give support to theories of the copper oxide materials based on the behavior of holes in antiferromagnets, and it also provides theoretical guidance for the interpretation of experimental photoemission data for the cuprates.Comment: (minor changes) RevTeX, 4 figures available on reques

Superconductivity and antiferromagnetism in a hard-core boson spin-1 model in two dimensions

A model of hard-core bosons and spin-1 sites with single-ion anisotropy is proposed to approximately describe hole pairs moving in a background of singlets and triplets with the aim of exploring the relationship between superconductivity and antiferromagnetism. The properties of this model at zero temperature were investigated using quantum Monte Carlo techniques. The most important feature found is the suppression of superconductivity, as long range coherence of preformed pairs, due to the presence of both antiferromagnetism and $S^z=\pm 1$ excitations. Indications of charge ordered and other phases are also discussed.Comment: One figure, one reference, adde

Anomalous low doping phase of the Hubbard model

We present results of a systematic Quantum-Monte-Carlo study for the single-band Hubbard model. Thereby we evaluated single-particle spectra (PES & IPES), two-particle spectra (spin & density correlation functions), and the dynamical correlation function of suitably defined diagnostic operators, all as a function of temperature and hole doping. The results allow to identify different physical regimes. Near half-filling we find an anomalous `Hubbard-I phase', where the band structure is, up to some minor modifications, consistent with the Hubbard-I predictions. At lower temperatures, where the spin response becomes sharp, additional dispersionless `bands' emerge due to the dressing of electrons/holes with spin excitatons. We present a simple phenomenological fit which reproduces the band structure of the insulator quantitatively. The Fermi surface volume in the low doping phase, as derived from the single-particle spectral function, is not consistent with the Luttinger theorem, but qualitatively in agreement with the predictions of the Hubbard-I approximation. The anomalous phase extends up to a hole concentration of 15%, i.e. the underdoped region in the phase diagram of high-T_c superconductors. We also investigate the nature of the magnetic ordering transition in the single particle spectra. We show that the transition to an SDW-like band structure is not accomplished by the formation of any resolvable `precursor bands', but rather by a (spectroscopically invisible) band of spin 3/2 quasiparticles. We discuss implications for the `remnant Fermi surface' in insulating cuprate compounds and the shadow bands in the doped materials.Comment: RevTex-file, 20 PRB pages, 16 figures included partially as gif. A full ps-version including ps-figures can be found at http://theorie.physik.uni-wuerzburg.de/~eder/condmat.ps.gz Hardcopies of figures (or the entire manuscript) can also be obtained by e-mail request to: [email protected]

Análise da série de preços do fruto açaí.

bitstream/CNPDIA-2010/12631/1/CT105-2009.pd

Hole photoproduction in insulating copper oxide

Basing on t-J model we calculate the k-dependence of a single hole photoproduction probability for CuO2 plane at zero doping. We also discuss the radiation of spin-waves which can substantially deform the shape of photoemission spectra.Comment: latex 8 pages, 3 figure

Spectral function of the spiral spin state in the trestle and ladder Hubbard model

Eder and Ohta have found a violation of the Luttinger rule in the spectral function for the t-t'-J model, which was interpreted as a possible breakdown of the Tomonaga-Luttinger(TL) description in models where electrons can pass each other. Here we have computed the spin correlation along with the spectral function for the one-dimensional t-t' Hubbard model and two-leg Hubbard ladder. By varying the Hubbard U we have identified that such a phenomenon is in fact a spinless-fermion-like behavior of holes moving in a spiral spin configuration that has a spin correlation length of the system size.Comment: 3 pages, RevTex, 8 figures in Postscript, to be published in Phys. Rev. B (rapid communication