UBV photometry of asteroid 433 Eros

UBV observations of asteroid 433 Eros were conducted on 17 nights during the winter of 1974/75. The peak-to-peak amplitude of the light curve varied from about 0.3 mag to nearly 1.4 mag. The absolute V magnitude, extrapolated to zero phase, is 10.85. Phase coefficients of 0.0245 mag/degree, 0.0009 mag/degree, and 0.0004 mag/degree were derived for V, B-V, and U-B, respectively. The zero-phase color of Eros (B-V = 0.88, U-B = 0.50) is representative of an S (silicaceous) compositional type asteroid. The color does not vary with rotation. The photometric behavior of Eros can be modeled by a cylinder with rounded ends having an axial ratio of about 2.3:1

On the Critical Behavior of the Uniform Susceptibility of a Fermi Liquid Near an Antiferromagnetic Transition with Dynamic Exponent z=2 z = 2

We compute the leading behavior of the uniform magnetic susceptibility, $\chi$, of a Fermi liquid near an antiferromagnetic transition with dynamic exponent $z=2$. Our calculation clarifies the role of triangular ``anomaly'' graphs in the theory and justifies the effective action used in previous work \cite{Hertz}. We find that at the $z=2$ critical point of a two dimensional material, $lim_{q \rightarrow 0} \chi (q,0) = \chi_0 - D T$ with $\chi_0$ and $D$ nonuniversal constants. For reasonable band structures we find that in a weak coupling approximation $D$ is small and positive. Our result suggests that the behavior observed in the quantum critical regime of underdoped high-$T_c$ superconductors are difficult to explain in a $z=2$ theory.Comment: 12 pages, uuencoded Postscript fil

On the Bilayer Coupling in the Yttrium-Barium Family of High Temperature Superconductors

We present and solve a model for the susceptibility of two CuO2 planes coupled by an interplane coupling J_perp and use the results to analyze a recent "cross-relaxation" NMR experiment on Y2Ba4Cu7O15. We deduce that in this material the product of J_perp and the maximum value of the in-plane susceptibility chi_max varies from approximately 0.2 at T = 200 K to 0.4 at T = 120 K and that this implies the existence of a temperature dependent in-plane spin correlation length. Using estimates of chi_max from the literature we find 5 meV < J_perp < 20 meV. We discuss the relation of the NMR results to neutron scattering results which have been claimed to imply that in YBa2Cu3O_{6+x} the two planes of a bilayer are perfectly anticorrelated. We also propose that the recently observed 41 meV excitation in YBa2Cu3O7 is an exciton pulled down below the superconducting gap by J_perp.Comment: 11 pages, 3 postscript figures (uuencoded and compressed

Diagrammatic Monte Carlo simulation of non-equilibrium systems

We generalize the recently developed diagrammatic Monte Carlo techniques for quantum impurity models from an imaginary time to a Keldysh formalism suitable for real-time and nonequilibrium calculations. Both weak-coupling and strong-coupling based methods are introduced, analysed and applied to the study of transport and relaxation dynamics in interacting quantum dots

Orbital dynamics: The origin of the anomalous optical spectra in ferromagnetic manganites

We discuss the role of orbital degeneracy in the transport properties of perovskite manganites, focusing in particular on the optical conductivity in the metallic ferromagnetic phase at low temperatures. Orbital degeneracy and strong correlations are described by an orbital t-J model which we treat in a slave-boson approach. Employing the memory-function formalism we calculate the optical conductivity, which is found to exhibit a broad incoherent component extending up to bare bandwidth accompanied by a strong suppression of the Drude weight. Further, we calculate the constant of T-linear specific heat. Our results are in overall agreement with experiment and suggest low-energy orbital fluctuations as the origin of the strongly correlated nature of the metallic phase of manganites.Comment: To appear in: Phys. Rev. B 58 (Rapid Communications), 1 November 199

Quantum critical effects on transition temperature of magnetically mediated p-wave superconductivity

We determine the behavior of the critical temperature of magnetically mediated p-wave superconductivity near a ferromagnetic quantum critical point in three dimensions, distinguishing universal and non-universal aspects of the result. We find that the transition temperature is non-zero at the critical point, raising the possibility of superconductivity in the ferromagnetic phase.Comment: 4 pages, 4 figure

Thermoelectric Figure of Merit of Strongly Correlated Superlattice Semiconductors

We solved the Anderson Lattice Hamiltonian to get the energy bands of a strongly correlated semiconductor by using slave boson mean field theory. The transport properties were calculated in the relaxation-time approximation,and the thermoelectric figure of merit was obtained for the strongly correlated semiconductor and its superlattice structures. We found that at room temperature $ZT$ can reach nearly 2 for the quantum wire lattice structure.We believe that it is possible to find high values of thermoelectric figure of merit from strongly correlated semiconductor superlattice systems.Comment: 4 pages, 3 figure

Optical-conductivity sum rule in cuprates and unconventional charge density waves: a short review

We begin with an overview of the experimental results for the temperature and doping dependences of the optical-conductivity spectral weight in cuprate superconductors across the whole phase diagram. Then we discuss recent attempts to explain the observed behavior of the spectral weight using reduced and full models with unconventional $d_{x^2-y^2}$ charge-density waves.Comment: 17 pages, RevTeX4, 4 EPS figures; Invited paper for a special issue of Low Temperature Physics dedicated to the 20th anniversary of HTS

Mesoscopic mean-field theory for spin-boson chains in quantum optical systems

We present a theoretical description of a system of many spins strongly coupled to a bosonic chain. We rely on the use of a spin-wave theory describing the Gaussian fluctuations around the mean-field solution, and focus on spin-boson chains arising as a generalization of the Dicke Hamiltonian. Our model is motivated by experimental setups such as trapped ions, or atoms/qubits coupled to cavity arrays. This situation corresponds to the cooperative (E⊗β) Jahn-Teller distortion studied in solid-state physics. However, the ability to tune the parameters of the model in quantum optical setups opens up a variety of novel intriguing situations. The main focus of this paper is to review the spin-wave theoretical description of this problem as well as to test the validity of mean-field theory. Our main result is that deviations from mean-field effects are determined by the interplay between magnetic order and mesoscopic cooperativity effects, being the latter strongly size-dependent