Unconventional properties of superconducting cuprates

We present an explanation of the unusual peak/dip/hump features observed in photoemission experiments on Bi2212 at $T \ll T_c$. We argue that these features arise from the interaction of the fermionic quasi-particles with overdamped spin fluctuations. We show that the strong spin-fermion interaction combined with the feedback effect on the spin damping due to superconductivity yields a Fermi-liquid form of the fermionic spectral function for $\omega < 2 \Delta$ where $\Delta$ is the maximum value of the superconducting gap, and a non-Fermi-liquid form for $\omega > 2 {\Delta}$. In the Fermi-liquid regime, the spectral function $A({\bf k}_F,\omega)$ displays a quasiparticle peak at $\omega = {\Delta}$; in the non-Fermi-liquid regime it possesses a broad maximum (hump) at $\omega \gg {\Delta}$. In between the two regimes, the spectral function has a dip at $\omega \sim 2 {\Delta}$. We argue that our theory also explains the tunneling data for the superconducting density of states.Comment: 4 pages, RevTeX, 4 eps figures embedded in the tex

Air quality monitoring for the International Space Station applicable to aircraft cabins and cockpits

New multigas measurement technology has been developed as part of and in parallel with a series of projects for the European Space Agency (ESA). Based on well-established Fourier transform infrared (FTIR) spectroscopy and novel calibration and analysis methods, ESA’s Analysing Interferometer for Ambient Air (ANITA) system has successfully demonstrated continuous air quality monitoring on the International Space Station (ISS). ANITA performed automatic multigas measurements in quasireal time with high sensitivity, specificity, stability and reliability. The novel analysis techniques are well suited also for general workplace air monitoring, industrial processes and other multicomponent measurement tasks.publishedVersio

Development of Cryogenic Filter Wheels for the HERSCHEL Photodetector Array Camera & Spectrometer (PACS)

This paper describes the two PACS Filter Wheels that are direct-drive rotational mechanisms operated at a temperature below 5K inside the PACS focal plane unit of the Herschel Satellite. The purpose of the mechanisms is to switch between filters. The rotation axis is pivoted to the support structure via a slightly preloaded pair of ball bearings and driven by a Cryotorquer. Position sensing is realized by a pair of Hall effect sensors. Powerless positioning at the filter positions is achieved by a magnetic ratchet system. The key technologies are the Cryotorquer design and the magnetic ratchet design in the low temperature range. Furthermore, we will report on lessons learned during the development and qualification of the mechanism and the paint

Ground-state van der Waals forces in planar multilayer magnetodielectrics

Within the frame of lowest-order perturbation theory, the van der Waals potential of a ground-state atom placed within an arbitrary dispersing and absorbing magnetodielectric multilayer system is given. Examples of an atom situated in front of a magnetodielectric plate or between two such plates are studied in detail. Special emphasis is placed on the competing attractive and repulsive force components associated with the electric and magnetic matter properties, respectively, and conditions for the formation of repulsive potential walls are given. Both numerical and analytical results are presented.Comment: 16 pages, 8 figures, minor correction

Electronic structure of underdoped cuprates

We consider a two-dimensional Fermi liquid coupled to low-energy commensurate spin fluctuations. At small coupling, the hole Fermi surface is large and centered around $Q =(\pi,\pi)$. We show that as the coupling increases, the shape of the quasiparticle Fermi surface and the spin-fermion vertex undergo a substantial evolution. At strong couplings, $g \gg \omega_0$, where $\omega_0$ is the upper cutoff in the spin susceptibility, the hole Fermi surface consists of small pockets centered at $(\pm \pi/2, \pm \pi/2)$. Simultaneously, the full spin-fermion vertex is much smaller than the bare one, and scales nearly linearly with $|q-Q|$, where $q$ is the momentum of the susceptibility. At intermediate couplings, there exist both, a large hole Fermi surface centered at $(\pi,\pi)$, and four hole pockets, but the quasiparticle residue is small everywhere except for the pieces of the pockets which face the origin of the Brillouin zone. The relevance of these results for recent photoemission experiments in $YBCO$ and $Bi2212$ systems is discussed.Comment: 19 pages, RevTeX, 15 figures embedded in the text, submitted to Phys. Rep., ps-file is also available at http://lifshitz.physics.wisc.edu/www/morr/morr_homepage.htm

High-resolution quantitative imaging of mammalian and bacterial cells using stable isotope mass spectrometry

Background: Secondary-ion mass spectrometry (SIMS) is an important tool for investigating isotopic composition in the chemical and materials sciences, but its use in biology has been limited by technical considerations. Multi-isotope imaging mass spectrometry (MIMS), which combines a new generation of SIMS instrument with sophisticated ion optics, labeling with stable isotopes, and quantitative image-analysis software, was developed to study biological materials. Results: The new instrument allows the production of mass images of high lateral resolution (down to 33 nm), as well as the counting or imaging of several isotopes simultaneously. As MIMS can distinguish between ions of very similar mass, such as ^{12}C^{15}N^{-} and ^{13}C^{14}N^{-}, it enables the precise and reproducible measurement of isotope ratios, and thus of the levels of enrichment in specific isotopic labels, within volumes of less than a cubic micrometer. The sensitivity of MIMS is at least 1,000 times that of ^{14}C autoradiography. The depth resolution can be smaller than 1 nm because only a few atomic layers are needed to create an atomic mass image. We illustrate the use of MIMS to image unlabeled mammalian cultured cells and tissue sections; to analyze fatty-acid transport in adipocyte lipid droplets using ^{13}C-oleic acid; to examine nitrogen fixation in bacteria using ^{15}N gaseous nitrogen; to measure levels of protein renewal in the cochlea and in post-ischemic kidney cells using ^{15}N-leucine; to study DNA and RNA co-distribution and uridine incorporation in the nucleolus using ^{15}N-uridine and ^{81}Br of bromodeoxyuridine or ^{14}C-thymidine; to reveal domains in cultured endothelial cells using the native isotopes ^{12}C, ^{16}O, ^{14}N and ^{31}P; and to track a few ^{15}N-labeled donor spleen cells in the lymph nodes of the host mouse. Conclusion: MIMS makes it possible for the first time to both image and quantify molecules labeled with stable or radioactive isotopes within subcellular compartments

Resonant Raman Scattering in Antiferromagnets

Two-magnon Raman scattering provides important information about electronic correlations in the insulating parent compounds of high-$T_c$ materials. Recent experiments have shown a strong dependence of the Raman signal in $B_{1g}$ geometry on the frequency of the incoming photon. We present an analytical and numerical study of the Raman intensity in the resonant regime. It has been previously argued by one of us (A.Ch) and D. Frenkel that the most relevant contribution to the Raman vertex at resonance is given by the triple resonance diagram. We derive an expression for the Raman intensity in which we simultaneously include the enhancement due to the triple resonance and a final state interaction. We compute the two-magnon peak height (TMPH) as a function of incident frequency and find two maxima at $\omega^{(1)}_{res} \approx 2\Delta + 3J$ and $\omega^{(2)}_{res} \approx 2\Delta + 8J$. We argue that the high-frequency maximum is cut only by a quasiparticle damping, while the low-frequency maximum has a finite amplitude even in the absence of damping. We also obtain an evolution of the Raman profile from an asymmetric form around $\omega^{(1)}_{res}$ to a symmetric form around $\omega^{(2)}_{res}$. We further show that the TMPH depends on the fermionic quasiparticle damping, the next-nearest neighbor hopping term $t^{\prime}$ and the corrections to the interaction vertex between light and the fermionic current. We discuss our results in the context of recent experiments by Blumberg et al. on $Sr_2CuO_2Cl_2$ and $YBa_2Cu_3O_{6.1}$ and R\"{u}bhausen et al. on $PrBa_2Cu_3O_7$ and show that the triple resonance theory yields a qualitative and to some extent also quantitative understanding of the experimental data.Comment: 19 pages, RevTeX, 16 figures embedded in the text, ps-file is also available at http://lifshitz.physics.wisc.edu/www/morr/morr_homepage.htm

NEAR: New Earths in the Alpha Cen Region (bringing VISIR as a "visiting instrument" to ESO-VLT-UT4)

By adding a dedicated coronagraph, ESO in collaboration with the Breakthrough Initiatives, modifies the Very Large Telescope mid-IR imager (VISIR) to further boost the high dynamic range imaging capability this instru- ment has. After the VISIR upgrade in 2012, where coronagraphic masks were first added to VISIR, it became evident that coronagraphy at a ground-based 8m-class telescope critically needs adaptive optics, even at wavelengths as long as 10μm. For VISIR, a work-horse observatory facility instrument in normal operations, this is ”easiest” achieved by bringing VISIR as a visiting instrument to the ESO-VLT-UT4 having an adaptive M2. This “visit” enables a meaningful search for Earth-like planets in the habitable zone around both α-Cen1,2. Meaningful here means, achieving a contrast of ≈ 10^(-6) within ≈ 0.8arcsec from the star while maintaining basically the normal sensitivity of VISIR. This should allow to detect a planet twice the diameter of Earth. Key components will be a diffractive coronagraphic mask, the annular groove phase mask (AGPM), optimized for the most sensitive spectral band-pass in the N-band, complemented by a sophisticated apodizer at the level of the Lyot stop. For VISIR noise filtering based on fast chopping is required. A novel internal chopper system will be integrated into the cryostat. This chopper is based on the standard technique from early radio astronomy, conceived by the microwave pioneer Robert Dicke in 1946, which was instrumental for the discovery of the 3K radio background

The ANITA Air Monitoring Programme and Instrumentation – ISS and other Applications

This paper gives a status report on the flight experiment ANITA (Analysing Interferometer for Ambient Air), the development status of the successor unit ANITA II and spin-off activity such as the use of an ANITA-type instrument on a submarine. The ANITA system represents a precursor for ANITA II, a permanent continuous trace gas monitoring system on the International Space Station (ISS). The measurement task in a submarine environment is similar to the analysis in the closed environment on the ISS except for the different trace gases present. A proposed test measurement campaign on a submarine in 2006 is outlined in the paper. The ANITA air analyser can detect and quantify quasi on-line and simultaneously 30 trace gases with sub-ppm detection limits in addition to carbon dioxide and water vapour [4, 10]. This crewed cabin air quality monitor allows the detection and monitoring of trace gas dynamics of a spacecraft atmosphere, providing continuous air monitoring as well as crew warning capability in case of malfunctions. ANITA will be accommodated in an EXPRESS Rack on the US LAB Destiny. The transportation to ISS is provided by the first flight of the Automated Transfer Vehicle (ATV). Unfortunately, this flight has been delayed until mid 2007. The ANITA team presently works on further improvements in the design and performance of ANITA

Figuring sequences on a super-smooth sample

An ion beam figuring facility is operational at the Centre Spatial de Liège since 1997. Its present capabilities are described. An extensive characterisation programme is running in order to determine the optimised parameters for various materials and operating conditions. In this frame, tests have been performed on a spherical gold-coated aluminium mirror plated in between with nickel. The nickel plating was used to be super-polished to a BRDF of 1 10-4 at 1 deg at 10 µm wavelength. Micro-roughness and etching rate measurements were realised and influence of ion bombardment on the coating has been established after removal of the gold coating. The gold coating removing was performed by using the ion beam flux. Finally, the mirror has been figured from the original sphere to a parabola. Surface characteristics evolution is also described in terms of micro-roughness and surface error. An overview of the research and development programmes related to this facility is given. Results of this technique and potential impact on optics fabrication are then briefly exposed.Etude du polissage ionique (II