464 research outputs found
Test for interlayer coherence in a quasi-two-dimensional superconductor
Peaks in the magnetoresistivity of the layered superconductor
-(BEDT-TTF)Cu(NCS), measured in fields T applied
within the layers, show that the Fermi surface is extended in the interlayer
direction and enable the interlayer transfer integral (
meV) to be deduced. However, the quasiparticle scattering rate is
such that , implying that
-(BEDT-TTF)Cu(NCS) meets the criterion used to identify
interlayer incoherence. The applicability of this criterion to anisotropic
materials is thus shown to be questionable.Comment: 5 pages, 4 figure
Evidence for structural and electronic instabilities at intermediate temperatures in -(BEDT-TTF)X for X=Cu[N(CN)]Cl, Cu[N(CN)]Br and Cu(NCS): Implications for the phase diagram of these quasi-2D organic superconductors
We present high-resolution measurements of the coefficient of thermal
expansion of the quasi-twodimensional
(quasi-2D) salts -(BEDT-TTF)X with X = Cu(NCS), Cu[N(CN)]Br
and Cu[N(CN)]Cl. At intermediate temperatures (B), distinct anomalies
reminiscent of second-order phase transitions have been found at
K and 45 K for the superconducting X = Cu(NCS) and Cu[N(CN)]Br salts,
respectively. Most interestingly, we find that the signs of the uniaxial
pressure coefficients of are strictly anticorrelated with those of
. We propose that marks the transition to a spin-density-wave
(SDW) state forming on minor, quasi-1D parts of the Fermi surface. Our results
are compatible with two competing order parameters that form on disjunct
portions of the Fermi surface. At elevated temperatures (C), all compounds show
anomalies that can be identified with a kinetic, glass-like
transition where, below a characteristic temperature , disorder in the
orientational degrees of freedom of the terminal ethylene groups becomes frozen
in. We argue that the degree of disorder increases on going from the X =
Cu(NCS) to Cu[N(CN)]Br and the Cu[N(CN)]Cl salt. Our results
provide a natural explanation for the unusual time- and cooling-rate
dependencies of the ground-state properties in the hydrogenated and deuterated
Cu[N(CN)]Br salts reported in the literature.Comment: 22 pages, 7 figure
A statistical model for the intrinsically broad superconducting to normal transition in quasi-two-dimensional crystalline organic metals
Although quasi-two-dimensional organic superconductors such as
-(BEDT-TTF)Cu(NCS) seem to be very clean systems, with apparent
quasiparticle mean-free paths of several thousand \AA, the superconducting
transition is intrinsically broad (e.g K wide for K).
We propose that this is due to the extreme anisotropy of these materials, which
greatly exacerbates the statistical effects of spatial variations in the
potential experienced by the quasiparticles. Using a statistical model, we are
able to account for the experimental observations. A parameter , which
characterises the spatial potential variations, may be derived from
Shubnikov-de Haas oscillation experiments. Using this value, we are able to
predict a transition width which is in good agreement with that observed in MHz
penetration-depth measurements on the same sample.Comment: 8 pages, 2 figures, submitted to J. Phys. Condens. Matte
Isotope effect in superconductors with coexisting interactions of phonon and nonphonon mechanisms
We examine the isotope effect of superconductivity in systems with coexisting
interactions of phonon and nonphonon mechanisms in addition to the direct
Coulomb interaction. The interaction mediated by the spin fluctuations is
discussed as an example of the nonphonon interaction. Extended formulas for the
transition temperature Tc and the isotope-effect coefficient alpha are derived
for cases (a) omega_np omega_D, where omega_np is
an effective cutoff frequency of the nonphonon interaction that corresponds to
the Debye frequency omega_D in the phonon interaction. In case (a), it is found
that the nonphonon interaction does not change the condition for the inverse
isotope effect, i.e., mu^* > lambda_ph/2, but it modifies the magnitude of
alpha markedly. In particular, it is found that a giant isotope shift occurs
when the phonon and nonphonon interactions cancel each other largely. For
instance, strong critical spin fluctuations may give rise to the giant isotope
effect. In case (b), it is found that the inverse isotope effect occurs only
when the nonphonon interaction and the repulsive Coulomb interaction, in total
effect, work as repulsive interactions against the superconductivity. We
discuss the relevance of the present result to some organic superconductors,
such as kappa-(ET)2Cu(NCS)2 and Sr2RuO4 superconductors, in which inverse
isotope effects have been observed, and briefly to high-Tc cuprates, in which
giant isotope effects have been observed.Comment: 4 pages, 2 figures, (with jpsj2.cls, ver.1.2), v2:linguistic
correction
Electronic Collective Modes and Superconductivity in Layered Conductors
A distinctive feature of layered conductors is the presence of low-energy
electronic collective modes of the conduction electrons. This affects the
dynamic screening properties of the Coulomb interaction in a layered material.
We study the consequences of the existence of these collective modes for
superconductivity. General equations for the superconducting order parameter
are derived within the strong-coupling phonon-plasmon scheme that account for
the screened Coulomb interaction. Specifically, we calculate the
superconducting critical temperature Tc taking into account the full
temperature, frequency and wave-vector dependence of the dielectric function.
We show that low-energy plasmons may contribute constructively to
superconductivity. Three classes of layered superconductors are discussed
within our model: metal-intercalated halide nitrides, layered organic materials
and high-Tc oxides. In particular, we demonstrate that the plasmon contribution
(electronic mechanism) is dominant in the first class of layered materials. The
theory shows that the description of so-called ``quasi-two-dimensional
superconductors'' cannot be reduced to a purely 2D model, as commonly assumed.
While the transport properties are strongly anisotropic, it remains essential
to take into account the screened interlayer Coulomb interaction to describe
the superconducting state of layered materials.Comment: Final version (minor changes) 14 pages, 6 figure
Распространенность инфекции HPV/p16+ среди пациентов с орофарингеальной плоскоклеточной карциномой в центре высокоспециализированной медицинской помощи в Южной Индии
Introduction. Oropharyngeal squamous cell carcinomas are often found to be associated with human papilloma virus (HPV) infection. The prevalence of HPV infection among oropharyngeal squamous cell carcinomas patients in India is comparatively lower to that of the same worldwide. Aim. To find out the prevalence of HPV infection among oropharyngeal squamous cell carcinomas patients who presented in our hospital.Settings and design. Retrospective cross-sectional study.Materials and methods. Tissue block of 60 patients with biopsy-proven oropharyngeal squamous cell carcinomas were subjected to immunohistochemistry for evaluating p16 expression. The p16 expression pattern was correlated with the demographic details. Data was entered in Microsoft Excel and Statistical Analysis was done with the help of SPSS version 22 (IBM Corp. Released, 2013. IBM SPSS Statistics for Windows, Version 22.0. Armonk, NY: IBM Corp.).Results. Prevalence of HPV infection in our study was found to be 11.7 %. 85.8 % of all p16-positive patients had moderate-well differentiated disease. 6 out of 7 p16-positive patients had higher T stage (T3–4). All the patients who were p16+ were found to have a higher Nodal stage (N2–3). 100 % of all p16+ patients were found to have stage IV disease.Conclusion. Prevalence of HPV infection was found to be similar to that of previous studies conducted in India. These patients also presented with advanced nodal disease at presentation and thereby, an advanced overall stage.Введение. Орофарингеальная плоскоклеточная карцинома часто связана с заражением вирусом папилломы человека (ВпЧ). Распространенность инфекции ВпЧ среди пациентов с данной патологией в Индии сравнительно ниже, чем в других странах.Цель исследования – определить распространенность инфекции ВпЧ среди пациентов с орофарингеальной плоскоклеточной карциномой, получавших лечение в нашей больнице.Дизайн исследования. Ретроспективное одномоментное исследование.Материалы и методы. Образцы тканей 60 пациентов с подтвержденным биопсией диагнозом «орофарингеальная плоскоклеточная карцинома» были исследованы иммуногистохимически на экспрессию p16. Было проведено сравнение профиля экспрессии p16 с демографическими данными. полученные результаты оценены с помощью программы Microsoft Excel. Статистический анализ выполнен с использованием программного обеспечения SPSS version 22 (IBM Corp. Released, 2013. IBM SPSS Statistics для Windows, версия 22.0, Армонк, Нью-Йорк: IBM Corp.).Результаты. Частота встречаемости ВпЧ в нашем исследовании составила 11,7 %. Среднеи высокодифференцированное заболевание наблюдалось у 85,8 % пациентов с положительной экспрессией p16. Шесть из 7 больных с такой экспрессией p16 имели более высокую T-стадию (T3–4), а все больные с таким показателем – высокую N-стадию (N2–3). У всех пациентов с положительной экспрессией p16 наблюдалось заболевание стадии IV.Заключение. Распространенность инфекции ВпЧ была близкой к значениям, полученным в других исследованиях в Индии. Для пациентов с этой инфекцией также были характерны вовлеченность лимфатических узлов (N-стадия) в патологический процесс и более высокая общая стадия заболевания
Comparative magnetotransport and Tc measurements on kappa-(BEDT-TTF)2Cu(SCN)2 under pressure
We compare magnetotransport measurements under pressure on the organic
superconductor -(BEDT-TTF)Cu(SCN) with different
pressure-media and discover that the results are pressure media dependent. This
pressure-medium dependence is thought to originate from the difference in
thermal contraction between the very soft and highly anisotropic sample and the
isotropically contracting, but solid pressure medium, thus resulting in
non-hydrostatic pressure on the sample. However, comparison of pressure
measurements with different media reveals a pressure-medium independent
correlation between the superconducting transition temperature, T,
and the size of the quasi 2-dimensional Fermi surface pocket and thus the quasi
2-dimensional carrier density in -(BEDT-TTF)Cu(SCN). The
observed pressure-induced increase in the quasi 2-dimensional carrier density
can be interpreted as a transfer of carriers from quasi 1-dimensional Fermi
surface sections, reminiscent of a mechanism in cuprate superconductors, where
pressure is known to transfer carriers from the insulating charge reservoir
layers into the conducting cuprate sheets.Comment: 11 pages, 6 figure
Identification and Structural Characterization of a New Three-Finger Toxin Hemachatoxin from Hemachatus haemachatus Venom
10.1371/journal.pone.0048112PLoS ONE710
Electronic Structure Calculation by First Principles for Strongly Correlated Electron Systems
Recent trends of ab initio studies and progress in methodologies for
electronic structure calculations of strongly correlated electron systems are
discussed. The interest for developing efficient methods is motivated by recent
discoveries and characterizations of strongly correlated electron materials and
by requirements for understanding mechanisms of intriguing phenomena beyond a
single-particle picture. A three-stage scheme is developed as renormalized
multi-scale solvers (RMS) utilizing the hierarchical electronic structure in
the energy space. It provides us with an ab initio downfolding of the global
band structure into low-energy effective models followed by low-energy solvers
for the models. The RMS method is illustrated with examples of several
materials. In particular, we overview cases such as dynamics of semiconductors,
transition metals and its compounds including iron-based superconductors and
perovskite oxides, as well as organic conductors of kappa-ET type.Comment: 44 pages including 38 figures, to appear in J. Phys. Soc. Jpn. as an
invited review pape
Incoherent Interplane Conductivity of kappa-(BEDT-TTF)2Cu[N(CN)2]Br
The interplane optical spectrum of the organic superconductor
kappa-(BEDT-TTF)2Cu[N(CN)2]Br was investigated in the frequency range from 40
to 40,000 cm-1. The optical conductivity was obtained by Kramers-Kronig
analysis of the reflectance. The absence of a Drude peak at low frequency is
consistent with incoherent conductivity but in apparent contradiction to the
metallic temperature dependence of the DC resistivity. We set an upper limit to
the interplane transfer integral of tb = 0.1 meV. A model of defect-assisted
interplane transport can account for this discrepancy. We also assign the
phonon lines in the conductivity to the asymmetric modes of the ET molecule.Comment: 7 pages with embedded figures, submitted to PR
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