Biconical critical dynamics

A complete two loop renormalization group calculation of the multicritical dynamics at a tetracritical or bicritical point in anisotropic antiferromagnets in an external magnetic field is performed. Although strong scaling for the two order parameters (OPs) perpendicular and parallel to the field is restored as found earlier, in the experimentally accessible region the effective dynamical exponents for the relaxation of the OPs remain different since their equal asymptotic values are not reached.Comment: 6 pages, 2 figures; some additions, corrected typo

Polymeric compositions and their method of manufacture

Filled polymer compositions are made by dissolving the polymer binder in a suitable sublimable solvent, mixing the filler material with the polymer and its solvent, freezing the resultant mixture, and subliming the frozen solvent from the mixture from which it is then removed. The remaining composition is suitable for conventional processing such as compression molding or extruding. A particular feature of the method of manufacture is pouring the mixed solution slowly in a continuous stream into a cryogenic bath wherein frozen particles of the mixture result. The frozen individual particles are then subjected to the sublimation

Critical slowing down in random anisotropy magnets

We study the purely relaxational critical dynamics with non-conserved order parameter (model A critical dynamics) for three-dimensional magnets with disorder in a form of the random anisotropy axis. For the random axis anisotropic distribution, the static asymptotic critical behaviour coincides with that of random site Ising systems. Therefore the asymptotic critical dynamics is governed by the dynamical exponent of the random Ising model. However, the disorder influences considerably the dynamical behaviour in the non-asymptotic regime. We perform a field-theoretical renormalization group analysis within the minimal subtraction scheme in two-loop approximation to investigate asymptotic and effective critical dynamics of random anisotropy systems. The results demonstrate the non-monotonic behaviour of the dynamical effective critical exponent $z_{\rm eff}$.Comment: 11 pages, 4 figures, style file include

Energetics of positron states trapped at vacancies in solids

We report a computational first-principles study of positron trapping at vacancy defects in metals and semiconductors. The main emphasis is on the energetics of the trapping process including the interplay between the positron state and the defect's ionic structure and on the ensuing annihilation characteristics of the trapped state. For vacancies in covalent semiconductors the ion relaxation is a crucial part of the positron trapping process enabling the localization of the positron state. However, positron trapping does not strongly affect the characteristic features of the electronic structure, e.g., the ionization levels change only moderately. Also in the case of metal vacancies the positron-induced ion relaxation has a noticeable effect on the calculated positron lifetime and momentum distribution of annihilating electron-positron pairs.Comment: Submitted to Physical Review B on 17 April 2007. Revised version submitted on 6 July 200

Heavily Irradiated N-in-p Thin Planar Pixel Sensors with and without Active Edges

We present the results of the characterization of silicon pixel modules employing n-in-p planar sensors with an active thickness of 150 $\mathrm{\mu}$m, produced at MPP/HLL, and 100-200 $\mathrm{\mu}$m thin active edge sensor devices, produced at VTT in Finland. These thin sensors are designed as candidates for the ATLAS pixel detector upgrade to be operated at the HL-LHC, as they ensure radiation hardness at high fluences. They are interconnected to the ATLAS FE-I3 and FE-I4 read-out chips. Moreover, the n-in-p technology only requires a single side processing and thereby it is a cost-effective alternative to the n-in-n pixel technology presently employed in the LHC experiments. High precision beam test measurements of the hit efficiency have been performed on these devices both at the CERN SpS and at DESY, Hamburg. We studied the behavior of these sensors at different bias voltages and different beam incident angles up to the maximum one expected for the new Insertable B-Layer of ATLAS and for HL-LHC detectors. Results obtained with 150 $\mathrm{\mu}$m thin sensors, assembled with the new ATLAS FE-I4 chip and irradiated up to a fluence of 4$\times$10$^{15}\mathrm{n}_{\mathrm{eq}}/\mathrm{cm}^2$, show that they are excellent candidates for larger radii of the silicon pixel tracker in the upgrade of the ATLAS detector at HL-LHC. In addition, the active edge technology of the VTT devices maximizes the active area of the sensor and reduces the material budget to suit the requirements for the innermost layers. The edge pixel performance of VTT modules has been investigated at beam test experiments and the analysis after irradiation up to a fluence of 5$\times$10$^{15}\mathrm{n}_{\mathrm{eq}}/\mathrm{cm}^2$ has been performed using radioactive sources in the laboratory.Comment: Proceedings for iWoRiD 2013 conference, submitted to JINS

Production and Characterisation of SLID Interconnected n-in-p Pixel Modules with 75 Micrometer Thin Silicon Sensors

The performance of pixel modules built from 75 micrometer thin silicon sensors and ATLAS read-out chips employing the Solid Liquid InterDiffusion (SLID) interconnection technology is presented. This technology, developed by the Fraunhofer EMFT, is a possible alternative to the standard bump-bonding. It allows for stacking of different interconnected chip and sensor layers without destroying the already formed bonds. In combination with Inter-Chip-Vias (ICVs) this paves the way for vertical integration. Both technologies are combined in a pixel module concept which is the basis for the modules discussed in this paper. Mechanical and electrical parameters of pixel modules employing both SLID interconnections and sensors of 75 micrometer thickness are covered. The mechanical features discussed include the interconnection efficiency, alignment precision and mechanical strength. The electrical properties comprise the leakage currents, tuning characteristics, charge collection, cluster sizes and hit efficiencies. Targeting at a usage at the high luminosity upgrade of the LHC accelerator called HL-LHC, the results were obtained before and after irradiation up to fluences of $10^{16}$ $\mathrm{n}_{\mathrm{eq}}/\mathrm{cm}^2$ (1 MeV neutrons).Comment: 16 pages, 22 figure

Thin n-in-p pixel sensors and the SLID-ICV vertical integration technology for the ATLAS upgrade at the HL-LHC

The R&D activity presented is focused on the development of new modules for the upgrade of the ATLAS pixel system at the High Luminosity LHC (HL-LHC). The performance after irradiation of n-in-p pixel sensors of different active thicknesses is studied, together with an investigation of a novel interconnection technique offered by the Fraunhofer Institute EMFT in Munich, the Solid-Liquid-InterDiffusion (SLID), which is an alternative to the standard solder bump-bonding. The pixel modules are based on thin n-in-p sensors, with an active thickness of 75 um or 150 um, produced at the MPI Semiconductor Laboratory (MPI HLL) and on 100 um thick sensors with active edges, fabricated at VTT, Finland. Hit efficiencies are derived from beam test data for thin devices irradiated up to a fluence of 4e15 neq/cm^2. For the active edge devices, the charge collection properties of the edge pixels before irradiation is discussed in detail, with respect to the inner ones, using measurements with radioactive sources. Beyond the active edge sensors, an additional ingredient needed to design four side buttable modules is the possibility of moving the wire bonding area from the chip surface facing the sensor to the backside, avoiding the implementation of the cantilever extruding beyond the sensor area. The feasibility of this process is under investigation with the FE-I3 SLID modules, where Inter Chip Vias are etched, employing an EMFT technology, with a cross section of 3 um x 10 um, at the positions of the original wire bonding pads.Comment: Proceedings for Pixel 2012 Conference, submitted to NIM A, 6 page

Field theory of bicritical and tetracritical points. III. Relaxational dynamics including conservation of magnetization (Model C)

We calculate the relaxational dynamical critical behavior of systems of $O(n_\|)\oplus O(n_\perp)$ symmetry including conservation of magnetization by renormalization group (RG) theory within the minimal subtraction scheme in two loop order. Within the stability region of the Heisenberg fixed point and the biconical fixed point strong dynamical scaling holds with the asymptotic dynamical critical exponent $z=2\phi/\nu-1$ where $\phi$ is the crossover exponent and $\nu$ the exponent of the correlation length. The critical dynamics at $n_\|=1$ and $n_\perp=2$ is governed by a small dynamical transient exponent leading to nonuniversal nonasymptotic dynamical behavior. This may be seen e.g. in the temperature dependence of the magnetic transport coefficients.Comment: 6 figure