He Scattering from Random Adsorbates, Disordered Compact Islands and Fractal Submonolayers: Intensity Manifestations of Surface Disorder

A theoretical study is made on He scattering from three fundamental classes of disordered ad-layers: (a) Translationally random adsorbates, (b) disordered compact islands and (c) fractal submonolayers. The implications of the results to experimental studies of He scattering from disordered surfaces are discussed, and a combined experimental-theoretical study is made for Ag submonolayers on Pt(111). Some of the main theoretical findings are: (1) Structural aspects of the calculated intensities from translationally random clusters were found to be strongly correlated with those of individual clusters. (2) Low intensity Bragg interference peaks appear even for scattering from very small ad-islands, and contain information on the ad-island local electron structure. (3) For fractal islands, just as for islands with a different structure, the off-specular intensity depends on the parameters of the He/Ag interaction, and does not follow a universal power law as previously proposed in the literature. In the experimental-theoretical study of Ag on Pt(111), we use first experimental He scattering data from low-coverage (single adsorbate) systems to determine an empirical He/Ag-Pt potential of good quality. Then, we carry out He scattering calculations for high coverage and compare with experiments. The conclusions are that the actual experimental phase corresponds to small compact Ag clusters of narrow size distribution, translationally disordered on the surface.Comment: 36 double-spaced pages, 10 figures; accepted by J. Chem. Phys., scheduled to appear March 8. More info available at http://www.fh.huji.ac.il/~dani

The Weyl-Lanczos Equations and the Lanczos Wave Equation in 4 Dimensions as Systems in Involution

Using the work by Bampi and Caviglia, we write the Weyl-Lanczos equations as an exterior differential system. Using Janet-Riquier theory, we compute the Cartan characters for all spacetimes with a diagonal metric and for the plane wave spacetime since all spacetimes have a plane wave limit. We write the Lanczos wave equation as an exterior differential system and, with assistance from Janet-Riquier theory, we find that it forms a system in involution. This result can be derived from the scalar wave equation itself. We compute its Cartan characters and compare them with those of the Weyl-Lanczos equations.Comment: 18 pages, latex, no figures, references correcte

Antiferromagnetic order in CeCoIn5 oriented by spin-orbital coupling

An incommensurate spin density wave ($Q$ phase) confined inside the superconducting state at high basal plane magnetic field is an unique property of the heavy fermion metal CeCoIn$_5$. The neutron scattering experiments and the theoretical studies point out that this state come out from the soft mode condensation of magnetic resonance excitations. We show that the fixation of direction of antiferromagnetic modulations by a magnetic field reported by Gerber et al., Nat. Phys. {\bf 10}, 126 (2014) is explained by spin-orbit coupling. This result, obtained on the basis of quite general phenomenological arguments, is supported by the microscopic derivation of the $\chi_{zz}$ susceptibility dependence on the mutual orientation of the basal plane magnetic field and the direction of modulation of spin polarization in a multi-band metal.Comment: 7 pages plus 2 pages with 2 figure

Structure Determination of Disordered Metallic Sub-Monolayers by Helium Scattering: A Theoretical and Experimental Study

An approach based on He scattering is used to develop an atomic-level structural model for an epitaxially grown disordered sub-monolayer of Ag on Pt(111) at 38K. Quantum scattering calculations are used to fit structural models to the measured angular intensity distribution of He atoms scattered from this system. The structure obtained corresponds to narrowly size-dispersed compact clusters with modest translational disorder, and not to fractals which might be expected due to the low surface temperature. The clusters have up to two layers in height, the lower one having few defects only. The relations between specific features of the angular scattering distribution, and properties such as the cluster sizes and shapes, the inter-cluster distance distribution etc., are discussed. The results demonstrate the usefulness of He scattering as a tool for unraveling new complex surface phases.Comment: 5 pages, 3 figures, to appear in Surf. Sci. Lett. Related papers available at http://neon.cchem.berkeley.edu/~dani/He-papers.htm

A note on the topological order of noncommutative Hall fluids

We evaluate the ground state degeneracy of noncommutative Chern-Simons models on the two-torus, a quantity that is interpreted as the "topological order" of associated phases of Hall fluids. We define the noncommutative theory via T-duality from an ordinary Chern-Simons model with non-abelian 't Hooft magnetic fluxes. Motivated by this T-duality, we propose a discrete family of noncommutative, non-abelian fluid models, arising as a natural generalization of the standard noncommutative Chern-Simons effective models. We compute the topological order for these universality classes, and comment on their possible microscopic interpretation.Comment: 14 page

Conservation of the Anegada Iguana (Cyclura pinguis)

The long-term survival of the Anegada Iguana (Cyclura pinguis) is uncertain. The species is in danger of becoming extinct due to habitat destruction, competition with feral livestock, and the introduction of non-native mammalian predators. In an effort to save the Anegada Iguana, the IUCN Iguana Specialist Group and the British Virgin Islands National Parks Trust began a concerted conservation effort in 1997. They initiated a headstart program in order to bolster the wild population until many of the problems facing the iguanas can be minimized or removed. Headstarted iguanas were released back into the wild in October of 2003 and 2004. This paper briefly reviews the natural history of C. pinguis and presents some preliminary results from the ongoing long-term monitoring of the subadult iguanas reintroduced to the wild

Conservation of the Anegada Iguana (Cyclura pinguis)

The long-term survival of the Anegada Iguana (Cyclura pinguis) is uncertain. The species is in danger of becoming extinct due to habitat destruction, competition with feral livestock, and the introduction of non-native mammalian predators. In an effort to save the Anegada Iguana, the IUCN Iguana Specialist Group and the British Virgin Islands National Parks Trust began a concerted conservation effort in 1997. They initiated a headstart program in order to bolster the wild population until many of the problems facing the iguanas can be minimized or removed. Headstarted iguanas were released back into the wild in October of 2003 and 2004. This paper briefly reviews the natural history of C. pinguis and presents some preliminary results from the ongoing long-term monitoring of the subadult iguanas reintroduced to the wild