Field strength formulation,lattice Bianchi identities and perturbation theory for non-Abelian models

We develop an analytical approach for studying lattice gauge theories within the plaquette representation where the plaquette matrices play the role of the fundamental degrees of freedom. We start from the original Batrouni formulation and show how it can be modified in such a way that each non-Abelian Bianchi identity contains only two connectors instead of four. In addition, we include dynamical fermions in the plaquette formulation. Using this representation we construct the low-temperature perturbative expansion for U(1)$U(1)$ and SU(N)$\mathit{SU}(N)$ models and discuss its uniformity in the volume. The final aim of this study is to give a mathematical background for working with non-Abelian models in the plaquette formulation.     

Controlled local filament growth and dissolution in Ag–Ge–Se

Memory cells based on the cation migration and filament formation and rupture in a solid electrolyte have attracted much interest due to low switching voltages and a prospective high scalability. In this study we indirectly visualized the growth and dissolution of the conductive filament in Ag–Ge–Se samples with Ag bottom electrodes by surface analysis with Conductive Atomic Force Microscopy (CAFM). By application of a negative voltage to the inert CAFM tip, conductive filaments were grown on the scanned area and they were dissolved under reversed bias. The local conductivity changes directly corresponded to changes in the topography, i.e. to the filament protrusion and dissolution. Topography changes could be circumvented by limiting the maximum current. By placing the CAFM tip on a random spot on the sample, filaments with a diameter as low as 20 nm were grown by local current–voltage measurements. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Silicon-based thin films as bottom electrodes in chalcogenide nonvolatile memories

The effect of the electrical resistivity of a silicon-germanium (SiGe) thin film on the phase transition in a GeSbTe (GST) chalcogenide alloy and the manufacturing aspect of the fabrication process of a chalcogenide memory device employing the SiGe film as bottom electrodes were investigated. While p-type SiGe bottom electrodes were formed using in situ doping techniques, n-type ones could be made in a different manner where phosphorus atoms diffused from highly doped silicon underlayers to undoped SiGe films. The p-n heterojunction did not form between the p-type GST and n-type SiGe layers, and the semiconduction type of the SiGe alloys did not influence the memory device switching. It was confirmed that an optimum resistivity value existed for memory operation in spite of proportionality of Joule heating to electrical resistivity. The very high resistivity of the SiGe film had no effect on the reduction of reset current, which might result from the resistance decrease of the SiGe alloy at high temperatures.     

Quantitative comparison of filtering methods in lattice QCD

We systematically compare filtering methods used to extract topological excitations (like instantons, calorons, monopoles and vortices) from lattice gauge configurations, namely APE-smearing and spectral decompositions based on lattice Dirac and Laplace operators. Each of these techniques introduces ambiguities, which can invalidate the interpretation of the results. We show, however, that all these methods, when handled with care, reveal very similar topological structures. Hence, these common structures are free of ambiguities and faithfully represent infrared degrees of freedom in the QCD vacuum. As an application we discuss an interesting power law for the clusters of filtered topological charge.     

2 + 1 flavor simulations of QCD with improved staggered quarks

The MILC Collaboration has been performing realistic simulations of full QCD with 2 + 1 flavors of improved staggered quarks. Our simulations allow for controlled continuum and chiral extrapolations. I present results for the light pseudoscalar sector: masses and decay constants, quark masses and Gasser-Leutwyler low-energy constants. In addition I will present some results for heavy-light mesons, decay constants and semileptonic form factors, obtained in collaboration with the HPQCD and Fermilab lattice Collaborations. Such calculations will help in the extraction of CKM matrix elements from experimental measurements.     

Two-colour laser excitation as a way to set an absolute energy scale in photodetachment-microscopy based electron spectrometry

A two-colour laser technique is developed for photodetachment microscopy, by means of microwave modulation of a CW single-mode dye laser. A phase modulation regime is achieved through an electro-optical LiNbO₃ crystal excited at the frequency 1.95 GHz. The two first sidebands created are selected by rejection of the other orders through a plane Fabry-Perot interferometer. With the resulting two-colour radiation, the photodetachment microscopy technique is applied to a beam of ³²S⁻ ions. It is shown that the superposition of the two resulting interference patterns can be used as a ‘spectral vernier’ to remove the uncertainty on the electric field and absolute energy scale. Without any initial assumption on the value F of the electric field in the laser-ion interaction region, a measure of F and of the electron affinity ^eA of Sulfur can be obtained. Putting 16 recordings of two-colour photodetachment interferograms together, with the only condition that F be the same for all experiments, one gets ^eA(³²S) = 16752.978(11) cm⁻¹, which is quite compatible, even though not as accurate, with the most recently recommended value ^eA(³²S) = 16752.9760(42) cm⁻¹. A proposal is made for going from an incoherent to a coherent two-colour photodetachment scheme, which would make photodetachment interferograms sensitive to a new degree of freedom.     

Opto-electrical properties of amorphous carbon thin film deposited from natural precursor camphor

A simple thermal chemical vapor deposition technique is employed for the pyrolysis of a natural precursor “camphor” and deposition of carbon films on alumina substrate at higher temperatures (600-900 °C). X-ray diffraction measurement reveals the amorphous structure of these films. The carbon films properties are found to significantly vary with the deposition temperatures. At higher deposition temperature, films have shown predominately sp²-bonded carbon and therefore, higher conductivity and lower optical band gap (Tauc gap). These amorphous carbon (a-C) films are also characterized with Raman and X-ray photoelectron spectroscopy. In addition, electrical and optical properties are measured. The thermoelectric measurement shows these as-grown a-C films are p-type in nature.     

Transition Temperature of Two-Degenerate-Flavour QCD in the Chiral Limit

We present the results for the transition temperature of quantum chromodynamics （QCD） with two degenerate flavours （Nf = 2） of Wilson quarks. On lattice 8^3 × 4 with 4 representing the temporal extent, by using the Ferrenberg-Swendsen reweighting method, we determine the critical β = 6/g^2 where the transition occurs, g is the coupling constant. On lattice 8^2 × 20 × 4, by using the axial vector Ward-Takahashi identity, we calculate the current quark mass amq, a is the lattice spacing. Assuming the O（4） scaling, the critical β in the chiral limit is determined. We calculate the p meson mass amp at zero temperature on lattice 8^3 × 20. By using the experimental p meson mass to set the scale, we obtain 194（1） MeV for the transition temperature in the chiral limit.