Anisotropy in the Antiferromagnetic Spin Fluctuations of Sr2RuO4

It has been proposed that Sr_2RuO_4 exhibits spin triplet superconductivity mediated by ferromagnetic fluctuations. So far neutron scattering experiments have failed to detect any clear evidence of ferromagnetic spin fluctuations but, instead, this type of experiments has been successful in confirming the existence of incommensurate spin fluctuations near q=(1/3 1/3 0). For this reason there have been many efforts to associate the contributions of such incommensurate fluctuations to the mechanism of its superconductivity. Our unpolarized inelastic neutron scattering measurements revealed that these incommensurate spin fluctuations possess c-axis anisotropy with an anisotropic factor \chi''_{c}/\chi''_{a,b} of \sim 2.8. This result is consistent with some theoretical ideas that the incommensurate spin fluctuations with a c-axis anisotropy can be a origin of p-wave superconductivity of this material.Comment: 5 pages, 3 figures; accepted for publication in PR

Computer-aided design of novel HIV-1 entry inhibitors blocking the virus envelope gp120 V3 loop

Aim. The object of this study was to implement computer-aided design of the water-soluble analog of glycolipid β -galactosylceramide (β-GalCer), which presents a potential HIV-1 entry inhibitor, by the analysis of intermolecular interactions of β-GalCer with the central region of the virus envelope gp120 V3 loop followed by synthesis of this glycolipid derivative and testing for antiviral activity. Methods. To reach the object of view, computer modeling procedures, such as quantum chemical calculations, molecular docking, molecular dynamics and free energy simulations, were involved in the studies in conjunction with chemical synthesis and anti-HIV-1 assay methods. Results. As a result, the high probability of exhibiting of antiviral activity was predicted for the designed β-GalCer analog. The data of molecular modeling were confirmed by those of primary medical trials of the synthesized compound. Conclusions. In the light of the findings obtained, the designed analog of β-GalCer may be considered as the basic structure for simulation of its more potent structural forms and for posterior selection of drug candidates most promising for synthesis and anti-HIV-1 assays. Keywords: HIV-1 gp120 V3 loop, glycolipids, computer modeling, chemical synthesis, anti-AIDS drugs.Мета. На основі аналізу міжмолекулярних взаємодій гліколіпіду β-галактозилцераміду (β-GalCer) з центральною областю петлі V3 білка gp120 оболонки вірусу здійснити комп’ютерне конструювання водорозчинного аналога β-GalCer – потенційного інгібітора адсорбції ВІЛ-1 – з наступним синтезом цього похідного гліколіпіду і тестуванням на противірусну активність. Методи. Комп’ютерне моделювання: квантово-хімічні розрахунки, молекулярний докінг, молекулярна динаміка і оцінка вільної енергії утворення надмолекулярних структур, а також методи хімічного синтезу та тестування на анти-ВІЛ активність. Результати. Для сконструйованого аналога β-GalCer передбачено високу ймовірність прояву противірусної активності. Дані молекулярного моделювання підтверджено результатами первинних медичних випробувань синтезованої хімічної сполуки. Висновки. Отриманий аналог β-GalCer можна розглядати як базову структуру для моделювання його більш ефективних модифікованих форм і подальшого відбору молекул, перспективних для синтезу і тестування на анти-ВІЛ активність. Ключові слова: петля V3 білка gp120 ВІЛ-1, гліколіпіди, комп’ютерне моделювання, хімічний синтез, лікарські препарати проти СНІДу.Цель. На основе анализа межмолекулярных взаимодействий гликолипида β-галактозилцерамида (β-GalCer) с центральной областью петли V3 белка gp120 оболочки вируса осуществить компьютерное конструирование водорастворимого аналога β-GalCer – потенциального ингибитора адсорбции ВИЧ-1 – с последующим синтезом этого производного гликолипида и тестированием на противовирусную активность. Методы. Компьютерное моделирование: квантово-химические расчеты, молекулярный докинг, молекулярная динамика и оценка свободной энергии образования надмолекулярных структур, а также методы химического синтеза и тестирования на анти-ВИЧ активность. Результаты. Для сконструированного аналога β-GalCer предсказана высокая вероятность проявления противовирусной активности. Данные молекулярного моделирования подтверждены результатами первичных медицинских испытаний синтезированного химического соединения. Выводы. Полученный аналог β-GalCer можно рассматривать как базовую структуру для моделирования его более эффективных модифицированных форм и последующего отбора молекул, перспективных для синтеза и тестирования на анти-ВИЧ активность. Ключевые слова: петля V3 белка gp120 ВИЧ-1, гликолипиды, компьютерное моделирование, химический синтез, лекарственные препараты против СПИДа

Low temperature electronic properties of Sr_2RuO_4 I: Microscopic model and normal state properties

Starting from the quasi one-dimensional kinetic energy of the d_{yz} and d_{zx} bands we derive a bosonized description of the correlated electron system in Sr_2RuO_4. At intermediate coupling the magnetic correlations have a quasi one-dimensional component along the diagonals of the basal plane of the tetragonal unit cell that accounts for the observed neutron scattering results. Together with two-dimensional correlations the model consistently accounts for the normal phase specific heat, cyclotron mass enhancement, static susceptibility, and Wilson ratio and implies an anomalous high temperature resistivity.Comment: 12 pages REVTEX, 6 figure

Electronic theory for the normal state spin dynamics in Sr2_2RuO4_4: anisotropy due to spin-orbit coupling

Using a three-band Hubbard Hamiltonian we calculate within the random-phase-approximation the spin susceptibility, $\chi({\bf q},\omega)$, and NMR spin-lattice relaxation rate, 1/T$_1$, in the normal state of the triplet superconductor Sr$_2$RuO$_4$ and obtain quantitative agreement with experimental data. Most importantly, we find that due to spin-orbit coupling the out-of-plane component of the spin susceptibility $\chi^{zz}$ becomes at low temperatures two times larger than the in-plane one. As a consequence strong incommensurate antiferromagnetic fluctuations of the quasi-one-dimensional $xz$- and $yz$-bands point into the $z$-direction. Our results provide further evidence for the importance of spin fluctuations for triplet superconductivity in Sr$_2$RuO$_4$.Comment: revised versio

An ARPES view on the high-Tc problem: phonons vs spin-fluctuations

We review the search for a mediator of high-Tc superconductivity focusing on ARPES experiment. In case of HTSC cuprates, we summarize and discuss a consistent view of electronic interactions that provides natural explanation of both the origin of the pseudogap state and the mechanism for high temperature superconductivity. Within this scenario, the spin-fluctuations play a decisive role in formation of the fermionic excitation spectrum in the normal state and are sufficient to explain the high transition temperatures to the superconducting state while the pseudogap phenomenon is a consequence of a Peierls-type intrinsic instability of electronic system to formation of an incommensurate density wave. On the other hand, a similar analysis being applied to the iron pnictides reveals especially strong electron-phonon coupling that suggests important role of phonons for high-Tc superconductivity in pnictides.Comment: A summary of the ARPES part of the Research Unit FOR538, http://for538.wmi.badw.d

Low temperature electronic properties of Sr_2RuO_4 II: Superconductivity

The body centered tetragonal structure of Sr_2RuO_4 gives rise to umklapp scattering enhanced inter-plane pair correlations in the d_{yz} and d_{zx} orbitals. Based on symmetry arguments, Hund's rule coupling, and a bosonized description of the in-plane electron correlations the superconducting order parameter is found to be a orbital-singlet spin-triplet with two spatial components. The spatial anisotropy is 7%. The different components of the order parameter give rise to two-dimensional gapless fluctuations. The phase transition is of third order. The temperature dependence of the pair density, specific heat, NQR, Knight shift, and susceptibility are in agreement with experimental results.Comment: 20 pages REVTEX, 3 figure

Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS

We present the results of a search for new, heavy particles that decay at a significant distance from their production point into a final state containing charged hadrons in association with a high-momentum muon. The search is conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS detector operating at the Large Hadron Collider. Production of such particles is expected in various scenarios of physics beyond the standard model. We observe no signal and place limits on the production cross-section of supersymmetric particles in an R-parity-violating scenario as a function of the neutralino lifetime. Limits are presented for different squark and neutralino masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final version to appear in Physics Letters

Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment

This paper describes an analysis of the angular distribution of W->enu and W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with the ATLAS detector at the LHC in 2010, corresponding to an integrated luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and the missing transverse energy, the W decay angular distribution projected onto the transverse plane is obtained and analysed in terms of helicity fractions f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw > 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour, are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017 +/- 0.030, where the first uncertainties are statistical, and the second include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables, revised author list, matches European Journal of Physics C versio

Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS

The chi_b(nP) quarkonium states are produced in proton-proton collisions at the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS detector. Using a data sample corresponding to an integrated luminosity of 4.4 fb^-1, these states are reconstructed through their radiative decays to Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes. This is interpreted as the chi_b(3P) system.Comment: 5 pages plus author list (18 pages total), 2 figures, 1 table, corrected author list, matches final version in Physical Review Letter

Measurement of the inclusive isolated prompt photon cross-section in pp collisions at sqrt(s)= 7 TeV using 35 pb-1 of ATLAS data

A measurement of the differential cross-section for the inclusive production of isolated prompt photons in pp collisions at a center-of-mass energy sqrt(s) = 7 TeV is presented. The measurement covers the pseudorapidity ranges |eta|<1.37 and 1.52<=|eta|<2.37 in the transverse energy range 45<=E_T<400GeV. The results are based on an integrated luminosity of 35 pb-1, collected with the ATLAS detector at the LHC. The yields of the signal photons are measured using a data-driven technique, based on the observed distribution of the hadronic energy in a narrow cone around the photon candidate and the photon selection criteria. The results are compared with next-to-leading order perturbative QCD calculations and found to be in good agreement over four orders of magnitude in cross-section.Comment: 7 pages plus author list (18 pages total), 2 figures, 4 tables, final version published in Physics Letters