Organocatalytic synthesis of axially chiral atropisomers

This review summarises the recent progress made in the organocatalytic synthesis of atropisomeric compounds. Methodologies based on dynamic kinetic resolution and direct access to BINOL-like biaryls are described. A particular emphasis is given to reaction mechanisms and to the development of strategies to obtain stable products by increasing the barrier to atropisomer interconversion during the reaction

A view from inside iron-based superconductors

Muon spin spectroscopy is one of the most powerful tools to investigate the microscopic properties of superconductors. In this manuscript, an overview on some of the main achievements obtained by this technique in the iron-based superconductors (IBS) are presented. It is shown how the muons allow to probe the whole phase diagram of IBS, from the magnetic to the superconducting phase, and their sensitivity to unravel the modifications of the magnetic and the superconducting order parameters, as the phase diagram is spanned either by charge doping, by an external pressure or by introducing magnetic and non-magnetic impurities. Moreover, it is highlighted that the muons are unique probes for the study of the nanoscopic coexistence between magnetism and superconductivity taking place at the crossover between the two ground-states.Comment: 28 pages, 18 figure

Evidence for impurity-induced frustration in La2CuO4

Zero-field muon spin rotation and magnetization measurements were performed in La2Cu{1-x}MxO4, for 0<x< 0.12, where Cu2+ is replaced either by M=Zn2+ or by M=Mg2+ spinless impurity. It is shown that while the doping dependence of the sublattice magnetization (M(x)) is nearly the same for both compounds, the N\'eel temperature (T_N(x)) decreases unambiguously more rapidly in the Zn-doped compound. This difference, not taken into account within a simple dilution model, is associated with the frustration induced by the Zn2+ impurity onto the Cu2+ antiferromagnetic lattice. In fact, from T_N(x) and M(x) the spin stiffness is derived and found to be reduced by Zn doping more significantly than expected within a dilution model. The effect of the structural modifications induced by doping on the exchange coupling is also discussed.Comment: 4 pages, 4 figure

The poisoning effect of Mn in LaFe(1-x)Mn(x)AsO(0.89)F(0.11): unveiling a quantum critical point in the phase diagram of iron-based superconductors

A superconducting-to-magnetic transition is reported for LaFe$_{1-x}$Mn$_x$AsO$_{0.89}$F$_{0.11}$ where a per thousand amount of Mn impurities is dispersed. By employing local spectroscopic techniques like muon spin rotation (muSR) and nuclear quadrupole resonance (NQR) on compounds with Mn contents ranging from x=0.025% to x=0.75%, we find that the electronic properties are extremely sensitive to the Mn impurities. In fact, a small amount of Mn as low as 0.2% suppresses superconductivity completely. Static magnetism, involving the FeAs planes, is observed to arise for x > 0.1% and becomes further enhanced upon increasing Mn substitution. Also a progressive increase of low energy spin fluctuations, leading to an enhancement of the NQR spin-lattice relaxation rate 1/T1, is observed upon Mn substitution. The analysis of 1/T1 for the sample closest to the the crossover between superconductivity and magnetism (x = 0.2%) points towards the presence of an antiferromagnetic quantum critical point around that doping level.Comment: 11 pages, 10 figure

Critical chain length and superconductivity emergence in oxygen-equalized pairs of YBa2Cu3O6.30

The oxygen-order dependent emergence of superconductivity in YBa2Cu3O6+x is studied, for the first time in a comparative way, on pair samples having the same oxygen content and thermal history, but different Cu(1)Ox chain arrangements deriving from their intercalated and deintercalated nature. Structural and electronic non-equivalence of pairs samples is detected in the critical region and found to be related, on microscopic scale, to a different average chain length, which, on being experimentally determined by nuclear quadrupole resonance (NQR), sheds new light on the concept of critical chain length for hole doping efficiency.Comment: 7 RevTex pages, 2 Postscript figures. Submitted to Phys. Rev.

New approaches to probing Minkowski functionals

We generalize the concept of the ordinary skew-spectrum to probe the effect of non-Gaussianity on the morphology of cosmic microwave background (CMB) maps in several domains: in real space (where they are commonly known as cumulant-correlators), and in harmonic and needlet bases. The essential aim is to retain more information than normally contained in these statistics, in order to assist in determining the source of any measured non-Gaussianity, in the same spirit as Munshi & Heavens skew-spectra were used to identify foreground contaminants to the CMB bispectrum in Planck data. Using a perturbative series to construct the Minkowski functionals (MFs), we provide a pseudo-C based approach in both harmonic and needlet representations to estimate these spectra in the presence of a mask and inhomogeneous noise. Assuming homogeneous noise, we present approximate expressions for error covariance for the purpose of joint estimation of these spectra. We present specific results for four different models of primordial non-Gaussianity local, equilateral, orthogonal and enfolded models, as well as non-Gaussianity caused by unsubtracted point sources. Closed form results of nextorder corrections to MFs too are obtained in terms of a quadruplet of kurt-spectra. We also use the method of modal decomposition of the bispectrum and trispectrum to reconstruct the MFs as an alternative method of reconstruction of morphological properties of CMB maps. Finally, we introduce the odd-parity skew-spectra to probe the odd-parity bispectrum and its impact on the morphology of the CMB sky. Although developed for the CMB, the generic results obtained here can be useful in other areas of cosmology

The onset of magnetism peaked around x=1/4 in optimally electron-doped LnFe(1-x)Ru(x)AsO(1-y)F(y) (Ln = La, Nd or Sm) superconductors

The appearance of static magnetism, nanoscopically coexisting with superconductivity, is shown to be a general feature of optimally electron-doped LnFe(1-x)Ru(x)AsO(1-y)F(y) superconductor (Ln - lanthanide ion) upon isovalent substitution of Fe by Ru. The magnetic ordering temperature T_N and the magnitude of the internal field display a dome-like dependence on x, peaked around x=1/4, with higher T_N values for those materials characterized by a larger z cell coordinate of As. Remarkably, the latter are also those with the highest superconducting transition temperature (T_c) for x=0. The reduction of T_c(x) is found to be significant in the x region of the phase diagram where the static magnetism develops. Upon increasing the Ru content superconductivity eventually disappears, but only at x=0.6.Comment: accepted for publication in PR

Correlated trends of coexisting magnetism and superconductivity in optimally electron-doped oxy-pnictides

We report on the recovery of the short-range static magnetic order and on the concomitant degradation of the superconducting state in optimally F-doped SmFe_(1-x)Ru_(x)AsO_0.85F_0.15 for 0.1< x<0.6. The two reduced order parameters coexist within nanometer-size domains in the FeAs layers and finally disappear around a common critical threshold x_c=0.6. Superconductivity and magnetism are shown to be closely related to two distinct well-defined local electronic environments of the FeAs layers. The two transition temperatures, controlled by the isoelectronic and diamagnetic Ru substitution, scale with the volume fraction of the corresponding environments. This fact indicates that superconductivity is assisted by magnetic fluctuations, which are frozen whenever a short-range static order appears, and totally vanish above the magnetic dilution threshold x_c.Comment: Approved for publication in Phys. Rev. Letter

Evaluating Health Performance and Inequalities in Marche region of Italy

A worldwide selection of models for measuring performance in health services was appraised, with the internationally recognised Health System Performance Assessment tool chosen for testing in a local health authority in the Marche Region of Italy, utilising local, regional, national and international comparisons. A complementary means of measuring health inequality involving the Concentration Index enabled a holistic evaluation of the local health environment. Whilst the approach addressed a comprehensive range of issues, limitations with data availability were found to present genuine constraints that require future action. Nevertheless, valuable lessons were learned for policy makers, with the relationship between socio-economic inequalities and systematic variations in health indicators highlighted. The Health System Performance Assessment tool presents the opportunity for strategic alignment in performance measurement. This article presents an overview of extensive piece of research