Density of Phonon States in Superconducting FeSe as a Function of Temperature and Pressure

The temperature and pressure dependence of the partial density of phonon states of iron atoms in superconducting Fe1.01Se was studied by 57Fe nuclear inelastic scattering (NIS). The high energy resolution allows for a detailed observation of spectral properties. A sharpening of the optical phonon modes and shift of all spectral features towards higher energies by ~4% with decreasing temperature from 296 K to 10 K was found. However, no detectable change at the tetragonal - orthorhombic phase transition around 100 K was observed. Application of a pressure of 6.7 GPa, connected with an increase of the superconducting temperature from 8 K to 34 K, results in an increase of the optical phonon mode energies at 296 K by ~12%, and an even more pronounced increase for the lowest-lying transversal acoustic mode. Despite these strong pressure-induced modifications of the phonon-DOS we conclude that the pronounced increase of Tc in Fe1.01Se with pressure cannot be described in the framework of classical electron-phonon coupling. This result suggests the importance of spin fluctuations to the observed superconductivity

Double-spiral magnetic structure of the Fe/Cr multilayer revealed by nuclear resonance scattering

We have studied the magnetization depth profiles in a [57Fe(dFe)/Cr(dCr)]x30 multilayer with ultrathin Fe layers and nominal thickness of the chromium spacers dCr 2.0 nm using nuclear resonance scattering of synchrotron radiation. The presence of a broad pure-magnetic half-order (1/2) Bragg reflection has been detected at zero external field. The joint fit of the reflectivity curves and Mossbauer spectra of reflectivity measured near the critical angle and at the "magnetic" peak reveals that the magnetic structure of the multilayer is formed by two spirals, one in the odd and another one in the even iron layers, with the opposite signs of rotation. The double-spiral structure starts from the surface with the almost antiferromagnetic alignment of the adjacent Fe layers. The rotation of the two spirals leads to nearly ferromagnetic alignment of the two magnetic subsystems at some depth, where the sudden turn of the magnetic vectors by ~180 deg (spin-flop) appears, and both spirals start to rotate in opposite directions. The observation of this unusual double-spiral magnetic structure suggests that the unique properties of giant magneto-resistance devices can be further tailored using ultrathin magnetic layers.Comment: 9 pages, 3 figure

A relativistic model of the NN-dimensional singular oscillator

Exactly solvable $N$-dimensional model of the quantum isotropic singular oscillator in the relativistic configurational $\vec r_N$-space is proposed. It is shown that through the simple substitutions the finite-difference equation for the $N$-dimensional singular oscillator can be reduced to the similar finite-difference equation for the relativistic isotropic three-dimensional singular oscillator. We have found the radial wavefunctions and energy spectrum of the problem and constructed a dynamical symmetry algebra.Comment: 8 pages, accepted for publication in J. Phys.

Relatively oxidized conditions for diamond formation at Udachnaya (Siberia)

Thanks to the physical strength of diamonds and their relatively unreactive chemical nature, their mineral inclusions may remain exceptionally preserved from alteration processes and chemical exchanges with surrounding minerals, fluids and/or melts following diamond formation. Cr-bearing spinels are relatively common inclusions found in peridotitic diamonds and important oxybarometers providing information about the oxygen fugacity (fO2) of their source mantle rocks. Here, we investigated a magnesiochromite-olivine touching pair in a diamond from the Udachnaya kimberlite (Siberia) by in situ single-crystal X-ray diffraction and energy-domain synchrotron Mossbauer spectroscopy, aiming to constrain the physical-chemical conditions of diamond formation and to explore the redox state of this portion of the Siberian craton when the diamond was formed. The P-T-fO(2) entrapment conditions of the inclusion pair, determined by thermo- and oxybarometric analyses, are similar to 5.7(0.4) GPa and similar to 1015(50) ? (although entrapment at higher T and re-equilibration during subsequent mantle storage are also possible) and fO(2) near the enstatite-magnesite-olivine-diamond (EMOD) buffer. The determined fO(2) is similar to, or slightly more oxidized than, those of xenoliths from Udachnaya, but whilst the xenoliths last equilibrated with the surrounding mantle just prior to their entrainment in the kimberlite at similar to 360 Ma, the last equilibration of the inclusion pair is much older, occurring at 3.5-3.1, similar to 2 or similar to 1.8 Ga before final encapsulation in its host diamond. Hence, the similarity between xenoliths and inclusion fO(2) values indicates that the modern redox state of this portion of the Siberian lithosphere was likely attained relatively early after its formation and may have persisted for billions of years after diamond formation, at least at the local scale. Moreover, the oxygen fugacity determination for the inclusion pair provides direct evidence of diamond formation near the EMOD buffer and is consistent with recent models suggesting relatively oxidized, water-rich CHO fluids as the most likely parents for lithospheric diamonds

Importance of correlation effects in hcp iron revealed by a pressure-induced electronic topological transition

We discover that hcp phases of Fe and Fe0.9Ni0.1 undergo an electronic topological transition at pressures of about 40 GPa. This topological change of the Fermi surface manifests itself through anomalous behavior of the Debye sound velocity, c/a lattice parameter ratio and M\"ossbauer center shift observed in our experiments. First-principles simulations within the dynamic mean field approach demonstrate that the transition is induced by many-electron effects. It is absent in one-electron calculations and represents a clear signature of correlation effects in hcp Fe

Polymorphism of IL-8 cytokine gene in patients with pancreatogenic peritonitis

ОСТРЫЙ ПАНКРЕАТИТПАНКРЕАТОГЕННЫЙ ПЕРИТОНИТИНТЕРЛЕЙКИН-8ПОЛИМОРФИЗМ ГЕНЕТИЧЕСКИЙИММУННЫЙ ОТВЕТЦИТОКИНЫЦель. Данное предварительное исследование проводилось с целью определения возможной связи генетического полиморфизма цитокина IL-8 (-251А/Т) с его влиянием на варианты клинического течения и исхода острого панкреатита, осложненного панкреатогенным перитонитом. Материал и методы. Данными для исследования были образцы ДНК из лейкоцитов периферической крови 143 человек: 83 пациента с острым панкреатитом, осложненным панкреатогенным перитонитом, 60 здоровых доноров без острого панкреатита в анамнезе как группа сравнения. Анализ полиморфизма гена цитокина IL-8 (-251А/Т) выполнялся методом полимеразной цепной реакции с последующим анализом длины рестрикционных фрагментов (PCR-RFLP). Результаты. Анализ частоты аллельных вариантов гена цитокина IL-8 (-251А/Т) выявил, что в группе здоровых доноров доминирующим вариантом в 45% случаев были гетерозиготы (генотип А/Т). При исследовании наблюдалась достоверно (р1). Среди оперированных пациентов наблюдалась достоверно (р1). Among patients after surgical treatment genotype A/T was less often met in comparison with the group without it (p<0.05). This may indicate the association of genotype A/T and favorable clinical course of pancreatogenic peritonitis (OR<1). Genotype A/A was rarely registered, which may be due to regional peculiarities of the patient’s genotype. Conclusions. This preliminary study suggests that the identification of genetic polymorphism of IL-8 (-251A/T) may be informative and serve as an additional criterion to predict both the clinical course and outcome of pancreatogenic peritonitis; it may also specify indications for surgical treatment. However, the possible role of IL-8 (-251A/T) cytokine polymorphism in the outcome of pancreatogenic peritonitis requires further carefully planned cohort investigations