Interacting Electrons on a Square Fermi Surface

Electronic states near a square Fermi surface are mapped onto quantum chains. Using boson-fermion duality on the chains, the bosonic part of the interaction is isolated and diagonalized. These interactions destroy Fermi liquid behavior. Non-boson interactions are also generated by this mapping, and give rise to a new perturbation theory about the boson problem. A case with strong repulsions between parallel faces is studied and solved. There is spin-charge separation and the square Fermi surface remains square under doping. At half-filling, there is a charge gap and insulating behavior together with gapless spin excitations. This mapping appears to be a general tool for understanding the properties of interacting electrons on a square Fermi surface.Comment: 25 pages, Nordita preprint 94/22

Hydrogen contamination in Ge-doped SiO[sub 2] thin films prepared by helicon activated reactive evaporation

Germanium-doped silicon oxidethin films were deposited at low temperature by using an improved helicon plasma assisted reactive evaporation technique. The origins of hydrogen contamination in the film were investigated, and were found to be H incorporation during deposition and postdeposition water absorption. The H incorporation during deposition was avoided by using an effective method to eliminate the residual hydrogen present in the depositionsystem. The microstructure, chemical bonds, chemical etch rate, and optical index of the films were studied as a function of the deposition conditions. Granular microstructures were observed in low-density films, and were found to be the cause of postdeposition water absorption. The granular microstructure was eliminated and the film was densified by increasing the helicon plasma power and substrate bias during deposition. A high-density film was shown to have no postdeposition water absorption and no OH detected by using a Fourier-transform infrared spectrometer

Bosonization of Fermi liquids

We bosonize a Fermi liquid in any number of dimensions in the limit of long wavelengths. From the bosons we construct a set of coherent states which are related with the displacement of the Fermi surface due to particle-hole excitations. We show that an interacting hamiltonian in terms of the original fermions is quadratic in the bosons. We obtain a path integral representation for the generating functional which in real time, in the semiclassical limit, gives the Landau equation for sound waves and in the imaginary time gives us the correct form of the specific heat for a Fermi liquid even with the corrections due to the interactions between the fermions. We also discuss the similarities between our results and the physics of quantum crystals.Comment: 42 pages, RevteX, preprint UIUC (1993

Spin-Charge separation in a model of two coupled chains

A model of interacting electrons living on two chains coupled by a transverse hopping $t_\perp$, is solved exactly by bosonization technique. It is shown that $t_\perp$ does modify the shape of the Fermi surface also in presence of interaction, although charge and spin excitations keep different velocities $u_\rho$, $u_\sigma$. Two different regimes occur: at short distances, $x\ll \xi = (u_\rho - u_\sigma)/4t_\perp$, the two chain model is not sensitive to $t_\perp$, while for larger separation $x\gg \xi$ inter--chain hopping is relevant and generates further singularities in the electron Green function besides those due to spin-charge decoupling. (2 figures not included. Figure requests: FABRIZIO@ITSSISSA)Comment: 12 pages, LATEX(REVTEX), SISSA 150/92/CM/M

Free-space quantum key distribution

A working free-space quantum key distribution (QKD) system has been developed and tested over a 205-m indoor optical path at Los Alamos National Laboratory under fluorescent lighting conditions. Results show that free-space QKD can provide secure real-time key distribution between parties who have a need to communicate secretly.Comment: 5 pages, 2 figures, 2 tables. To be published in Physical review A on or about 1 April 199

Ground state phases of the Half-Filled One-Dimensional Extended Hubbard Model

Using quantum Monte Carlo simulations, results of a strong-coupling expansion, and Luttinger liquid theory, we determine quantitatively the ground state phase diagram of the one-dimensional extended Hubbard model with on-site and nearest-neighbor repulsions U and V. We show that spin frustration stabilizes a bond-ordered (dimerized) state for U appr. V/2 up to U/t appr. 9, where t is the nearest-neighbor hopping. The transition from the dimerized state to the staggered charge-density-wave state for large V/U is continuous for U up to appr. 5.5 and first-order for higher U.Comment: 4 pages, 4 figure

Correlation functions for a two-dimensional electron system with bosonic interactions and a square Fermi surface

We calculate zero-temperature correlation functions for a model of 2D interacting electrons with short-range interactions and a square Fermi surface. The model was arrived at by mapping electronic states near a square Fermi surface with Hubbard-like interactions onto one-dimensional quantum chains, retaining terms which can be written in terms of bosonic density operators. Interactions between orthogonal chains, corresponding to orthogonal faces of the square Fermi surface, are neglected. The correlation functions become sums of Luttinger-type correlation functions due to the bosonic model. However, the correlation function exponents differ in form from those of the Luttinger model. As a consequence, the simple scaling relations found to exist between the Luttinger model exponents, do not carry over to the leading exponents of our model. We find that for repulsive effective interactions, charge-density wave/spin-density wave instabilities are dominant. We do not consider d-wave instabilities here.Comment: 12 pages, no figures; to be published in Physical Review

Bosonization of the Low Energy Excitations of Fermi Liquids

We bosonize the low energy excitations of Fermi Liquids in any number of dimensions in the limit of long wavelengths. The bosons are coherent superposition of electron-hole pairs and are related with the displacement of the Fermi Surface in some arbitrary direction. A coherent-state path integral for the bosonized theory is derived and it is shown to represent histories of the shape of the Fermi Surface. The Landau equation for the sound waves is shown to be exact in the semiclassical approximation for the bosons.Comment: 10 pages, RevteX, P-93-03-027 (UIUC

Microbial iron mats at the Mid-Atlantic Ridge and evidence that Zetaproteobacteria may be restricted to iron-oxidizing marine systems

© The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in PLoS One 10 (2015): e0119284, doi:10.1371/journal.pone.0119284 .Chemolithoautotrophic iron-oxidizing bacteria play an essential role in the global iron cycle. Thus far, the majority of marine iron-oxidizing bacteria have been identified as Zetaproteobacteria, a novel class within the phylum Proteobacteria. Marine iron-oxidizing microbial communities have been found associated with volcanically active seamounts, crustal spreading centers, and coastal waters. However, little is known about the presence and diversity of iron-oxidizing communities at hydrothermal systems along the slow crustal spreading center of the Mid-Atlantic Ridge. From October to November 2012, samples were collected from rust-colored mats at three well-known hydrothermal vent systems on the Mid-Atlantic Ridge (Rainbow, Trans-Atlantic Geotraverse, and Snake Pit) using the ROV Jason II. The goal of these efforts was to determine if iron-oxidizing Zetaproteobacteria were present at sites proximal to black smoker vent fields. Small, diffuse flow venting areas with high iron(II) concentrations and rust-colored microbial mats were observed at all three sites proximal to black smoker chimneys. A novel, syringe-based precision sampler was used to collect discrete microbial iron mat samples at the three sites. The presence of Zetaproteobacteria was confirmed using a combination of 16S rRNA pyrosequencing and single-cell sorting, while light micros-copy revealed a variety of iron-oxyhydroxide structures, indicating that active iron-oxidizing communities exist along the Mid-Atlantic Ridge. Sequencing analysis suggests that these iron mats contain cosmopolitan representatives of Zetaproteobacteria, but also exhibit diversity that may be uncommon at other iron-rich marine sites studied to date. A meta-analysis of publically available data encompassing a variety of aquatic habitats indicates that Zetaproteobacteria are rare if an iron source is not readily available. This work adds to the growing understanding of Zetaproteobacteria ecology and suggests that this organism is likely locally restricted to iron-rich marine environments but may exhibit wide-scale geographic distribution, further underscoring the importance of Zetaproteobacteria in global iron cycling.This work was supported by grants from the National Science Foundation [grants OCE-0926805 (DE and JAB), OCE-1155754 (DE), and OCE-1131109 (GWL)] and the National Aeronautics and Space Administration [NNX12AG20G (GWL and DE)]