Diffraction by a perfectly conducting rectangular cylinder which is illuminated by an array of line sources

The geometrical theory of diffraction (GTD) is employed to analyze the radiation from a perfectly-conducting rectangular cylinder illuminated by an array of line sources. The excitation of the cylinder by a single electric or magnetic current line source is considered first, and a solution which includes contributions from the geometrical optics rays and all singly- and doubly-diffracted rays is obtained. A new diffraction coefficient valid in the transition regions of the shadow and reflection boundaries is employed to obtain a continuous total field, except for negligible discontinuities in the doubly-diffracted field at its shadow boundaries. Patterns calculated by the GTD method are found to be in excellent agreement with those calculated from an integral equation formulation. Using superposition the solution for array or aperture excitation of the rectangular cylinder is obtained. A computer program for this solution is included

Correlation Functions of Multisite Interaction Spin-S models on the Bethe-like Lattices

Multisite interaction spin-S models in an external magnetic field are studied recursively on the Bethe-like lattices. The transfer-matrix method is extended to calculate exactly the two-spin correlation functions. The exact expressions for the correlation length and magnetic susceptibility are derived for spin-1/2 models. The singularity of the correlation length with critical index $\nu =1$ and the proportionality of magnetic susceptibility to correlation length in the second order phase transition region of spin-1/2 ferromagnetic models on the Bethe-like lattices are established analytically.Comment: 13 pages, In Press Int. J. Mod. Phys.

Optical spectroscopy study on single crystalline LaFeAsO

Millimeter-sized single crystals of LaFeAsO were grown from NaAs flux and the in-plane optical properties were studied over a wide frequency range. A sizable electronic correlation effect was indicated from the analysis of the free-carrier spectral weight. With decreasing temperature from 300 K, we observed a continuous suppression of the spectral weight near 0.6 eV. But a spin-density-wave gap formation at lower energy scale was seen only in the broken-symmetry state. We elaborate that both the itinerancy and local spin interactions of Fe\emph{3d} electrons are present for the FeAs-based systems; however, the establishment of the long-range magnetic order at low temperature has a dominantly itinerant origin.Comment: 4 figures, 5 page

Where is the jet quenching in Pb+Pb collisions at 158 AGeV?

Because of the rapidly falling particle spectrum at large $p_T$ from jet fragmentation at the CERN SPS energy, the high-$p_T$ hadron distribution should be highly sensitive to parton energy loss inside a dense medium as predicted by recent perturbative QCD (pQCD) studies. A careful analysis of recent data from CERN SPS experiments via pQCD calculation shows little evidence of energy loss. This implies that either the life-time of the dense partonic matter is very short or one has to re-think about the problem of parton energy loss in dense matter. The hadronic matter does not seem to cause jet quenching in $Pb+Pb$ collisions at the CERN SPS. High-$p_T$ two particle correlation in the azimuthal angle is proposed to further clarify this issue.Comment: 4 pages with 2 ps figures. Minors changes are made in the text with updated references. Revised version to appear in Phys. Rev. Letter

Optical study of phase transitions in single-crystalline RuP

RuP single crystals of MnP-type orthorhombic structure were synthesized by the Sn flux method. Temperature-dependent x-ray diffraction measurements reveal that the compound experiences two structural phase transitions, which are further confirmed by enormous anomalies shown in temperature-dependent resistivity and magnetic susceptibility. Particularly, the resistivity drops monotonically upon temperature cooling below the second transition, indicating that the material shows metallic behavior, in sharp contrast with the insulating ground state of polycrystalline samples. Optical conductivity measurements were also performed in order to unravel the mechanism of these two transitions. The measurement revealed a sudden reconstruction of band structure over a broad energy scale and a significant removal of conducting carriers below the first phase transition, while a charge-density-wave-like energy gap opens below the second phase transition.Comment: 5 pages, 6 figure

Thermal Hall Conductivity as a Probe of Gap Structure in Multi-band Superconductors: The Case of Ba1−xKxFe2As2\rm Ba_{1-x}K_xFe_2As_2

The sign and profile of the thermal Hall conductivity $\kappa_{xy}$ gives important insights into the gap structure of multi-band superconductors. With this perspective, we have investigated $\kappa_{xy}$ and the thermal conductivity $\kappa_{xx}$ in $\rm Ba_{1-x}K_xFe_2As_2$ which display large peak anomalies in the superconducting state. The anomalies imply that a large hole-like quasiparticle (qp) population exists below the critical temperature $T_c$. We show that the qp mean-free-path inferred from $\kappa_{xx}$ reproduces the observed anomaly in $\kappa_{xy}$, providing a consistent estimate of a large qp population. Further, we demonstrate that the hole-like signal is consistent with a theoretical scenario where despite potentially large gap variations on the electron pockets, the minimal homogeneous gap of the superconducting phase resides at a hole pocket. Implications for probing the gap structure in the broader class of pnictide superconductors are discussed.Comment: 5 pages, 4 figures. Orientation significantly updated from previous (0811.4668v1) reflecting new theoretical understanding of experimental results and physical implications. Introduction, discussion, and figures updated including additional figure for model calculatio