Phase Diagram of the Hubbard Model: Beyond the Dynamical Mean Field

The Dynamical Cluster Approximation (DCA) is used to study non-local corrections to the dynamical mean field phase diagram of the two-dimensional Hubbard model. Regions of antiferromagnetic, d-wave superconducting, pseudo-gapped non-Fermi liquid, and Fermi liquid behaviors are found, in rough agreement with the generic phase diagram of the cuprates. The non-local fluctuations beyond the mean field both suppress the antiferromagnetism and mediate the superconductivity.Comment: 4 pages, 5 eps figures, submitted to PR

Noise-Activated Escape from a Sloshing Potential Well

We treat the noise-activated escape from a one-dimensional potential well of an overdamped particle, to which a periodic force of fixed frequency is applied. We determine the boundary layer behavior, and the physically relevant length scales, near the oscillating well top. We show how stochastic behavior near the well top generalizes the behavior first determined by Kramers, in the case without forcing. Both the case when the forcing dies away in the weak noise limit, and the case when it does not, are examined. We also discuss the relevance of various scaling regimes to recent optical trap experiments.Comment: 9 pages, no figures, REVTeX, expanded versio

Rotating system for four-dimensional transverse rms-emittance measurements

Knowledge of the transverse four-dimensional beam rms-parameters is essential for applications that involve lattice elements that couple the two transverse degrees of freedom (planes). Of special interest is the removal of inter-plane correlations to reduce the projected emittances. A dedicated ROtating System for Emittance measurements (ROSE) has been proposed, developed, and successfully commissioned to fully determine the four-dimensional beam matrix. This device has been used at the High Charge injector (HLI) at GSI using a beam line which is composed of a skew quadrupole triplet, a normal quadrupole doublet, and ROSE. Mathematical algorithms, measurements, and results for ion beams of 83Kr13+ at 1.4 MeV/u are reported in this paper.Comment: 11 pages, 10 figure

d-wave Superconductivity in the Hubbard Model

The superconducting instabilities of the doped repulsive 2D Hubbard model are studied in the intermediate to strong coupling regime with help of the Dynamical Cluster Approximation (DCA). To solve the effective cluster problem we employ an extended Non Crossing Approximation (NCA), which allows for a transition to the broken symmetry state. At sufficiently low temperatures we find stable d-wave solutions with off-diagonal long range order. The maximal $T_c\approx 150K$ occurs for a doping $\delta\approx 20$ and the doping dependence of the transition temperatures agrees well with the generic high-$T_c$ phase diagram.Comment: 5 pages, 5 figure

Buffering plasmons in nanoparticle waveguides at the virtual-localized transition

We study the plasmonic energy transfer from a locally excited nanoparticle (LE-NP) to a linear array of small NPs and we obtain the parametric dependence of the response function. An analytical expression allows us to distinguish the extended resonant states and the localized ones, as well as an elusive regime of virtual states. This last appears when the resonance width collapses and before it becomes a localized state. Contrary to common wisdom, the highest excitation transfer does not occur when the system has a well defined extended resonant state but just at the virtual-localized transition, where the main plasmonic modes have eigenfrequencies at the passband edge. The slow group velocity at this critical frequency enables the excitation buffering and hence favors a strong signal inside the chain. A similar situation should appear in many other physical systems. The extreme sensitivity of this transition to the waveguide and LE-NP parameters provides new tools for plasmonics.Comment: Regular article: 7 pages and 5 figure

41Ca in tooth enamel. part I: A biological signature of neutron exposure in atomic bomb survivors

The detection of 41Ca atoms in tooth enamel using accelerator mass spectrometry is suggested as a method capable of reconstructing thermal neutron exposures from atomic bomb survivors in Hiroshima and Nagasaki. In general, 41Ca atoms are produced via thermal neutron capture by stable 40Ca. Thus any 41Ca atoms present in the tooth enamel of the survivors would be due to neutron exposure from both natural sources and radiation from the bomb. Tooth samples from five survivors in a control group with negligible neutron exposure were used to investigate the natural 41Ca content in tooth enamel, and 16 tooth samples from 13 survivors were used to estimate bomb-related neutron exposure. The results showed that the mean 41Ca/Ca isotope ratio was (0.17 ± 0.05) × 10-14 in the control samples and increased to 2 × 10-14 for survivors who were proximally exposed to the bomb. The 41Ca/Ca ratios showed an inverse correlation with distance from the hypocenter at the time of the bombing, similar to values that have been derived from theoretical free-in-air thermal-neutron transport calculations. Given that γ-ray doses were determined earlier for the same tooth samples by means of electron spin resonance (ESR, or electron paramagnetic resonance, EPR), these results can serve to validate neutron exposures that were calculated individually for the survivors but that had to incorporate a number of assumptions (e.g. shielding conditions for the survivors).Fil: Wallner, A.. Ludwig Maximilians Universitat; Alemania. Universitat Technical Zu Munich; Alemania. Universidad de Viena; AustriaFil: Ruhm, W.. Helmholtz Center Munich German Research Center For Environmental Health; Alemania. Ludwig Maximilians Universitat; AlemaniaFil: Rugel, G.. Ludwig Maximilians Universitat; Alemania. Universitat Technical Zu Munich; AlemaniaFil: Nakamura, N.. Radiation Effects Research Foundation; JapónFil: Arazi, Andres. Universitat Technical Zu Munich; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Faestermann, T.. Universitat Technical Zu Munich; AlemaniaFil: Knie, K.. Universitat Technical Zu Munich; Alemania. Ludwig Maximilians Universitat; AlemaniaFil: Maier, H. J.. Ludwig Maximilians Universitat; AlemaniaFil: Korschinek, G.. Universitat Technical Zu Munich; Alemani

On polynomial solutions of Heun equation

By making use of a recently developed method to solve linear differential equations of arbitrary order, we find a wide class of polynomial solutions to the Heun equation. We construct the series solution to the Heun equation before identifying the polynomial solutions. The Heun equation extended by the addition of a term, - \s/x, is also amenable for polynomial solutions.Comment: 4 pages, No figur

Dynamical Cluster Approximation Employing FLEX as a Cluster Solver

We employ the Dynamical Cluster Approximation (DCA) in conjunction with the Fluctuation Exchange Approximation (FLEX) to study the Hubbard model. The DCA is a technique to systematically restore the momentum conservation at the internal vertices of Feynman diagrams relinquished in the Dynamical Mean Field Approximation (DMFA). FLEX is a perturbative diagrammatic approach in which classes of Feynman diagrams are summed over analytically using geometric series. The FLEX is used as a tool to investigate the complementarity of the DCA and the finite size lattice technique with periodic boundary conditions by comparing their results for the Hubbard model. We also study the microscopic theory underlying the DCA in terms of compact (skeletal) and non-compact diagrammatic contributions to the thermodynamic potential independent of a specific model. The significant advantages of the DCA implementation in momentum space suggests the development of the same formalism for the frequency space. However, we show that such a formalism for the Matsubara frequencies at finite temperatures leads to acausal results and is not viable. However, a real frequency approach is shown to be feasible.Comment: 15 pages, 24 figures. Submitted to Physical Review B as a Regular Articl