1,114 research outputs found
Does Light Quality Influence Arabidopsis thaliana Growth in Controlled Environments?
This study examines the use of diverse lamp types, with inherently different spectral attributes, to determine light quality influence on Arabidopsis thaliana growth in controlled environments
Experimental investigation of the competing orders and quantum criticality in hole- and electron-doped cuprate superconductors
We investigate the issues of competing orders and quantum criticality in cuprate superconductors via experimental studies of the high-field thermodynamic phase diagrams and the quasiparticle tunneling spectroscopy. Substantial field-induced quantum fluctuations are found in all cuprates investigated, and the corresponding correlation with quasiparticle spectra suggest that both electron- (n-type) and hole-doped (p-type) cuprate superconductors are in close proximity to a quantum critical point that separates a pure superconducting (SC) phase from a phase consisting of coexisting SC and a competing order. We further suggests that the relevant competing order is likely a spin-density wave (SDW) or a charge density wave (CDW), which can couple efficiently to an in-plane Cu-O bond stretching longitudinal optical (LO) phonon mode in the p-type cuprates but not in the n-type cuprates. This cooperative interaction may account for the pseudogap phenomenon above T, only in the p-type cuprate superconductors
Macroscopic evidence for quantum criticality and field-induced quantum fluctuations in cuprate superconductors
We present macroscopic experimental evidence for field-induced microscopic
quantum fluctuations in different hole- and electron-type cuprate
superconductors with varying doping levels and numbers of CuO layers per
unit cell. The significant suppression of the zero-temperature in-plane
magnetic irreversibility field relative to the paramagnetic field in all
cuprate superconductors suggests strong quantum fluctuations due to the
proximity of the cuprates to quantum criticality.Comment: 3 figures. To appear in Phys. Rev. B, Rapid Communications (2007).
For correspondence, contact: Nai-Chang Yeh (e-mail: [email protected]
Interactive grid-access using GridSolve and Giggle
General purpose Problem Solving Environments (PSEs) like Matlab are widely used in the fields of science for development of new algorithms. If a lot of computing power is required to run these algorithms, today's PSEs lack support for accessing the distributed infrastructures of the organisation (i.e. grids), which limits the size of the problems that can be solved. This contribution shows a new approach to utilize the grid from within PSEs without major adjustments by the user. The primary tools are GridSolve and and the grid-middleware gLite. The applicability is illustrated by an exemplary algorithm (Mandelbrot calculations)
Low temperature specific heat of the heavy fermion superconductor PrOsSb
We report the magnetic field dependence of the low temperature specific heat
of single crystals of the first Pr-based heavy fermion superconductor
PrOsSb. The low temperature specific heat and the magnetic phase
diagram inferred from specific heat, resistivity and magnetisation provide
compelling evidence of a doublet ground state and hence superconductivity
mediated by quadrupolar fluctuations. This establishes PrOsSb as a
very strong contender of superconductive pairing that is neither
electron-phonon nor magnetically mediated.Comment: 4 pages, 4 figure
Electronic Scattering Effects in Europium-Based Iron Pnictides
In a comprehensive study, we investigate the electronic scattering effects in
EuFe(AsP) by using Fourier-transform infrared
spectroscopy. In spite of the fact that Eu local moments order around
\,K, the overall optical response is strikingly similar
to the one of the well-known Ba-122 pnictides. The main difference lies within
the suppression of the lower spin-density-wave gap feature. By analysing our
spectra with a multi-component model, we find that the high-energy feature
around 0.7\,eV -- often associated with Hund's rule coupling -- is highly
sensitive to the spin-density-wave ordering, this further confirms its direct
relationship to the dynamics of itinerant carriers. The same model is also used
to investigate the in-plane anisotropy of magnetically detwinned
EuFeAs in the antiferromagnetically ordered state, yielding a
higher Drude weight and lower scattering rate along the crystallographic
-axis. Finally, we analyse the development of the room temperature spectra
with isovalent phosphor substitution and highlight changes in the scattering
rate of hole-like carriers induced by a Lifshitz transition
First US Performance Measurements of Next Generation 3D USCT 2.5 Transducers
The KITâs 3D Ultrasound Computer Tomography (USCT) II system has a multistatic setup of 2041 ultrasound transducers with approx. 1.5 MHz 6dB bandwidth and 36⊠3 dB opening angle for 2.5 MHz. To increase the region of interest for a next USCT generation, the opening angle should be increased to approx. 60⊠and the bandwidth doubled. To increase the opening angle the size of the transducer elements was decreased to approximately half the size. A circular aperture was chosen for homogenicity of the radiation pattern in 3D. The transducer design utilizes piezo-fibres by the established Fraunhofer IMT piezo-fibre composite technology. The fibres were fabricated from PZT powder using the polysulfone spinning process. 17 fibres were positioned with a mechanical mask and filled with a matrix of epoxy. From this rod piezo composite discs were sawed and polarized. Electrodes were generated by silver-filled epoxy adhesive on the top and bottom side. Materials for acoustic backing is a Tungsten-Polyurethane composite and for acoustic matching ia aluminium oxide composite material (TMM4). Ultrasound characteristics were evaluated quantitatively with a Onda HNC-400 hydrophone in a 3-axis water tank for a randomly selected sample transducer (see Fig. a.)). Characteristics evaluated were the pressure field as function over frequency and angle in the far-field (see Fig. b.)), following the use-case. For excitation a linear encoded chirp was used, for SNR improvements averaging of measurements (64 to 256 times) was conducted. The analysis compensated for the hydrophonâs frequency and angular damping characteristics. The presented results show that the desired characteristics were mostly achieved: the 6 dB bandwidth could be vastly improved by roughly 200% (see Fig. d.)). The 6 dB pressure opening angle was approx. 50⊠(see Fig. c.)), not completly fullfilling the simulated expectations, an improvement by 31% was achieved. The results are promising for the next 3D USCT III generation
Thermodynamics of the Spin Luttinger-Liquid in a Model Ladder Material
The phase diagram in temperature and magnetic field of the metal-organic,
two-leg, spin-ladder compound (C5H12N)2CuBr4 is studied by measurements of the
specific heat and the magnetocaloric effect. We demonstrate the presence of an
extended spin Luttinger-liquid phase between two field-induced quantum critical
points and over a broad range of temperature. Based on an ideal spin-ladder
Hamiltonian, comprehensive numerical modelling of the ladder specific heat
yields excellent quantitative agreement with the experimental data across the
complete phase diagram.Comment: 4 pages, 4 figures, updated refs and minor changes to the text,
version accepted for publication in Phys. Rev. Let
Superconductivity and crystalline electric field effects in the filled skutterudite series Pr(OsRu)Sb
X-ray powder diffraction, magnetic susceptibility , and electrical
resistivity measurements were made on single crystals of the filled
skutterudite series Pr(OsRu)Sb. One end of the series
() is a heavy fermion superconductor with a superconducting critical
temperature K, while the other end () is a conventional
superconductor with K. The lattice constant decreases
approximately linearly with increasing Ru concentration . As Ru (Os) is
substituted for Os (Ru), decreases nearly linearly with substituent
concentration and exhibits a minimum with a value of K at , suggesting that the two types of superconductivity compete with one
another. Crystalline electric field (CEF) effects in and
due to the splitting of the Pr nine-fold degenerate Hund's
rule multiplet are observed throughout the series, with the splitting
between the ground state and the first excited state increasing monotonically
as increases. The fits to the and data are
consistent with a doublet ground state for all values of x,
although reasonable fits can be obtained for a ground state for
values near the end member compounds ( or ).Comment: 10 pages, 8 figures, submitted to Phys. Rev.
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