802 research outputs found
Singular Effect of Disorder on Electronic Transport in Strong Coupling Electron-Phonon Systems
We solve the disordered Holstein model in three dimensions considering the
phonon variables to be classical. After mapping out the phases of the `clean'
strong coupling problem, we focus on the effect of disorder at strong
electron-phonon (EP) coupling. The presence of even weak disorder (i)
enormously enhances the resistivity (\rho) at T=0, simultaneously suppressing
the density of states at the Fermi level, (ii) suppresses the temperature
dependent increase of \rho, and (iii) leads to a regime with d\rho/dT <0. We
locate the origin of these anomalies in the disorder induced tendency towards
polaron formation, and the associated suppression in effective carrier density
and mobility. These results, explicitly at `metallic' density, are of direct
relevance to disordered EP materials like covalent semiconductors, the
manganites, and to anomalous transport in the A-15 compounds.Comment: Final versio
The fabrication of reproducible superconducting scanning tunneling microscope tips
Superconducting scanning tunneling microscope tips have been fabricated with
a high degree of reproducibility. The fabrication process relies on sequential
deposition of superconducting Pb and a proximity-coupled Ag capping layer onto
a Pt/Ir tip. The tips were characterized by tunneling into both normal-metal
and superconducting films. The simplicity of the fabrication process, along
with the stability and reproducibility of the tips, clear the way for tunneling
studies with a well-characterized, scannable superconducting electrode.Comment: 4 pages, 3 figures, REVTeX. Submitted to Rev. Sci. Instru
Josephson Effect in Pb/I/NbSe2 Scanning Tunneling Microscope Junctions
We have developed a method for the reproducible fabrication of
superconducting scanning tunneling microscope (STM) tips. We use these tips to
form superconductor/insulator/superconductor tunnel junctions with the STM tip
as one of the electrodes. We show that such junctions exhibit fluctuation
dominated Josephson effects, and describe how the Josephson product IcRn can be
inferred from the junctions' tunneling characteristics in this regime. This is
first demonstrated for tunneling into Pb films, and then applied in studies of
single crystals of NbSe2. We find that in NbSe2, IcRn is lower than expected,
which could be attributed to the interplay between superconductivity and the
coexisting charge density wave in this material.Comment: 3 pages, 2 figures. Presented at the New3SC-4 meeting, San Diego,
Jan. 16-21 200
Universal transport in 2D granular superconductors
The transport properties of quench condensed granular superconductors are
presented and analyzed. These systems exhibit transitions from insulating to
superconducting behavior as a function of inter-grain spacing.
Superconductivity is characterized by broad transitions in which the resistance
drops exponentially with reducing temperature. The slope of the log R versus T
curves turns out to be universaly dependent on the normal state film resistance
for all measured granular systems. It does not depend on the material, critical
temperature, geometry, or experimental set-up. We discuss possible physical
scenarios to explain these findings.Comment: 4 pages, 3 figure
Development and demonstration of manufacturing processes for fabricating graphite/LARC 160 polyimide structural elements
The development and demonstration of manufacturing technologies for the structural application of Celion graphite/LARC-160 polyimide composite material is discussed. Process development and fabrication of demonstration components are discussed. Process development included establishing quality assurance of the basic composite material and processing, nondestructive inspection of fabricated components, developing processes for specific structural forms, and qualification of processes through mechanical testing. Demonstration components were fabricated. The demonstration components consisted of flat laminates, skin/stringer panels, honeycomb panels, chopped fiber compression moldings, and a technology demonstrator segment (TDS) representative of the space shuttle aft body flap
Penerapan Fuzzy Inference System pada Prediksi Curah Hujan di Surabaya Utara
Musim penghujan yang terjadi di Indonesia antara bulan Oktober hingga April dengan puncak curah hujan tertinggi di bulan Desember. Namun terdapat kemungkinan terjadinya anomali cuaca bahkan penyimpangan iklim. Hal tersebut ditandai dengan berubahnya puncak curah hujan. Jika kondisi tersebut diabaikan, maka dapat mengakibatkan banjir di beberapa kota khususnya Surabaya Utara. Kondisi ini disebabkan karena di Surabaya merupakan aktivitas perdagangan dan kurang efektifnya manajemen banjir oleh pihak terkait. Hal tersebut perlu penanganan khusus, sehingga curah hujan diprediksikan dengan menerapkan aturan penalaran dasar dan logika fuzzy dengan menerapkan metode Fuzzy Inference System. Penelitian ini menggunakan enam variabel yang mempengaruhi terjadinya hujan berupa suhu udara, kelembaban relatif, kecepatan angin, tekanan udara, total lapisan awan, dan lama penyinaran matahari. Dalam hal ini digunakan keakuratan untuk memverifikasi hasil prediksi curah hujan, yaitu Brier Score. Hasil yang didapat dari penelitian ini diperoleh keakuratan prediksi curah hujan sebesar 77,68% dari sebelas eksperimen
Pinching and Probing of Polygonal Grain Boundaries
In this study, sub-angstrom spatial resolution is achieved in mapping and
spectroscopy of atoms and bonds within polygonal grain boundaries (GBs) of
graphite using Scanning Tunneling Microscopy (STM). Robust van Hove
singularities (VHS) are observed in addition to edge states under ambient
conditions. The bias-dependent nature of these states reveals metallic traits
of GB, through the charge accumulation and dissipation of localized electronic
states. Utilizing a surface elastic deformation technique induced by STM tip
allows pico-pinching of the GB, providing insights into its mechanical strength
as well as in-situ strain-induced modification of their unique spectroscopy,
revealing a tendency toward flattening of the electronic energy band
dispersion. An initial atomic-level experimental technique of probing
spin-polarized magnetic states is demonstrated, suggesting different densities
for spin-up and spin-down states within a spin-degenerate band structure
potentially applicable in spin transport or quantum spin sensing.Comment: Submitte
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