366 research outputs found
Recent developments in the determination of the amplitude and phase of quantum oscillations for the linear chain of coupled orbits
De Haas-van Alphen oscillations are studied for Fermi surfaces (FS)
illustrating the model proposed by Pippard in the early sixties, namely the
linear chain of orbits coupled by magnetic breakdown. This FS topology is
relevant for many multiband quasi-two dimensional (q-2D) organic metals such as
-(BEDT-TTF)Cu(NCS) and
-(BEDT-TTF)CoBr(CHCl) which are considered in
detail. Whereas the Lifshits-Kosevich model only involves a first order
development of field- and temperature-dependent damping factors, second order
terms may have significant contribution on the Fourier components amplitude for
such q-2D systems at high magnetic field and low temperature. The strength of
these second order terms depends on the relative value of the involved damping
factors, which are in turns strongly dependent on parameters such as the
magnetic breakdown field, effective masses and, most of all, effective
Land\'{e} factors. In addition, the influence of field-dependent Onsager phase
factors on the oscillation spectra is considered.Comment: arXiv admin note: text overlap with arXiv:1304.665
Nature of bonding and electronic structure in MgB2, a boron intercalation superconductor
Chemical bonding and electronic structure of MgB2, a boron-based newly
discovered superconductor, is studied using self-consistent band structure
techniques. Analysis of the transformation of the band structure for the
hypothetical series of graphite - primitive graphite - primitive graphite-like
boron - intercalated boron, shows that the band structure of MgB2 is
graphite-like, with pi-bands falling deeper than in ordinary graphite. These
bands possess a typically delocalized and metallic, as opposed to covalent,
character. The in-plane sigma-bands retain their 2D covalent character, but
exhibit a metallic hole-type conductivity. The coexistence of 2D covalent
in-plane and 3D metallic-type interlayer conducting bands is a peculiar feature
of MgB2. We analyze the 2D and 3D features of the band structure of MgB2 and
related compounds, and their contributions to conductivity.Comment: 4 pages in revtex, 3 figures in 4 separate EPS file
Comparison of the Fermi-surface topologies of kappa-(BEDT-TTF)_2 Cu(NCS)_2 and its deuterated analogue
We have measured details of the quasi one-dimensional Fermi-surface sections
in the organic superconductor kappa-(BEDT-TTF)_2 Cu(NCS)_2 and its deuterated
analogue using angle-dependent millimetre-wave techniques. There are
significant differences in the corrugations of the Fermi surfaces in the
deuterated and undeuterated salts. We suggest that this is important in
understanding the inverse isotope effect, where the superconducting transition
temperature rises on deuteration. The data support models for superconductivity
which invoke electron-electron interactions depending on the topological
properties of the Fermi surface
Coronal Temperature Diagnostic Capability of the Hinode/X-Ray Telescope Based on Self-Consistent Calibration
The X-Ray Telescope (XRT) onboard the Hinode satellite is an X-ray imager
that observes the solar corona with unprecedentedly high angular resolution
(consistent with its 1" pixel size). XRT has nine X-ray analysis filters with
different temperature responses. One of the most significant scientific
features of this telescope is its capability of diagnosing coronal temperatures
from less than 1 MK to more than 10 MK, which has never been accomplished
before. To make full use of this capability, accurate calibration of the
coronal temperature response of XRT is indispensable and is presented in this
article. The effect of on-orbit contamination is also taken into account in the
calibration. On the basis of our calibration results, we review the
coronal-temperature-diagnostic capability of XRT
Transport criticality of the first-order Mott transition in a quasi-two-dimensional organic conductor, -(BEDT-TTF)Cu[N(CN)]Cl
An organic Mott insulator, -(BEDT-TTF)Cu[N(CN)]Cl, was
investigated by resistance measurements under continuously controllable He gas
pressure. The first-order Mott transition was demonstrated by observation of
clear jump in the resistance variation against pressure. Its critical endpoint
at 38 K is featured by vanishing of the resistive jump and critical divergence
in pressure derivative of resistance, , which are consistent with the prediction of the dynamical mean field
theory and have phenomenological correspondence with the liquid-gas transition.
The present results provide the experimental basis for physics of the Mott
transition criticality.Comment: 4 pages, 5 figure
Molecular characterization of a novel ssRNA ourmia-like virus from the rice blast fungus Magnaporthe oryzae
In this study we characterize a novel positive and single stranded RNA (ssRNA) mycovirus isolated from the rice field isolate of Magnaporthe oryzae Guy11. The ssRNA contains a single open reading frame (ORF) of 2,373 nucleotides in length and encodes an RNA-dependent RNA polymerase (RdRp) closely related to ourmiaviruses (plant viruses) and ourmia-like mycoviruses. Accordingly, we name this virus Magnaporthe oryzae ourmia-like virus 1 (MOLV1). Although phylogenetic analysis suggests that MOLV1 is closely related to ourmia and ourmia-like viruses, it has some features never reported before within the Ourmiavirus genus. 3' RLM-RACE (RNA ligase-mediated rapid amplification of cDNA ends) and extension poly(A) tests (ePAT) suggest that the MOLV1 genome contains a poly(A) tail whereas the three cytosine and the three guanine residues present in 5' and 3' untranslated regions (UTRs) of ourmia viruses are not observed in the MOLV1 sequence. The discovery of this novel viral genome supports the hypothesis that plant pathogenic fungi may have acquired this type of viruses from their host plants
Imaging fluorescence lifetime modulation of a ruthenium-based dye in living cells: the potential for oxygen sensing
Fluorescence lifetime measurements of long excited-state lifetime, oxygen-quenched ruthenium dyes are emerging as methods for intracellular oxygen sensing. Fluorescence lifetime imaging microscopy (FLIM) studies in cells have been reported previously. Many current FLIM systems use high repetition rate (âŒ107 Hz) lasers optimized for nanosecond lifetime measurements, making measurement of long, microsecond lifetime fluorophores difficult. Here, we present an experimental approach for obtaining a large temporal dynamic range in a FLIM system by using a low repetition rate (101 Hz), high output, nitrogen pumped dye laser and a wide-field, intensified CCD camera for image detection. We explore the feasibility of the approach by imaging the oxygen-sensitive dye tris(2,2âČ-bipyridyl)dichloro-ruthenium(II) hexahydrate (RTDP) in solution and in living cells. We demonstrate the ability of the system to resolve 60% variations in RTDP fluorescence lifetime upon oxygen cycling in solution. Furthermore, the FLIM system was able to resolve an increase in RTDP fluorescence lifetime in cultured human epithelial cells under diminished oxygen conditions. The technique may be useful in developing methods for quantifying intracellular oxygen concentrations.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48916/2/d31406.pd
Evidence of Andreev bound states as a hallmark of the FFLO phase in -(BEDT-TTF)Cu(NCS)
Superconductivity is a quantum phenomena arising, in its simplest form, from
pairing of fermions with opposite spin into a state with zero net momentum.
Whether superconductivity can occur in fermionic systems with unequal number of
two species distinguished by spin, atomic hyperfine states, flavor, presents an
important open question in condensed matter, cold atoms, and quantum
chromodynamics, physics. In the former case the imbalance between spin-up and
spin-down electrons forming the Cooper pairs is indyced by the magnetic field.
Nearly fifty years ago Fulde, Ferrell, Larkin and Ovchinnikov (FFLO) proposed
that such imbalanced system can lead to exotic superconductivity in which pairs
acquire finite momentum. The finite pair momentum leads to spatially
inhomogeneous state consisting of of a periodic alternation of "normal" and
"superconducting" regions. Here, we report nuclear magnetic resonance (NMR)
measurements providing microscopic evidence for the existence of this new
superconducting state through the observation of spin-polarized quasiparticles
forming so-called Andreev bound states.Comment: 6 pages, 5 fig
Phase Transition in \nu=2 Bilayer Quantum Hall State
The Hall-plateau width and the activation energy were measured in the bilayer
quantum Hall state at filling factor \nu=2, 1 and 2/3, by changing the total
electron density and the density ratio in the two quantum wells. Their behavior
are remarkably different from one to another. The \nu=1 state is found stable
over all measured range of the density difference, while the \nu=2/3$ state is
stable only around the balanced point. The \nu=2 state, on the other hand,
shows a phase transition between these two types of the states as the electron
density is changed.Comment: 5 pages including figures, RevTe
On the Relationship Between the Critical Temperature and the London Penetration Depth in Layered Organic Superconductors
We present an analysis of previously published measurements of the London
penetration depth of layered organic superconductors. The predictions of the
BCS theory of superconductivity are shown to disagree with the measured zero
temperature, in plane, London penetration depth by up to two orders of
magnitude. We find that fluctuations in the phase of the superconducting order
parameter do not determine the superconducting critical temperature as the
critical temperature predicted for a Kosterlitz--Thouless transition is more
than an order of magnitude greater than is found experimentally for some
materials. This places constraints on theories of superconductivity in these
materials.Comment: 5 pages, 1 figur
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