Energetic stability and magnetic properties of Mn dimers in silicon

We present an accurate first-principles study of magnetism and energetics of single Mn impurities and Mn dimers in Si. Our results, in general agreement with available experiments, show that (i) Mn atoms tend to aggregate, the formation energy of dimers being lower than the sum of the separate constituents, (ii) ferromagnetic coupling is favored between the Mn atoms constituting the dimers in p-type Si, switching to an antiferromagnetic coupling in n-type Si, (iii) Mn atoms show donors (acceptor) properties in p-type (n-type) Si, therefore they tend to compensate doping, while dimers being neutral or acceptors allow for Si to be doped p-type. (C) 2004 American Institute of Physics

Giant follicular cysts extended in pterygo-maxillary fossa, antro-naso-ethmoidal and orbital space associated to exophtalmos and diplopia in young patients

Abstract Follicular cysts develop from the enamel epithelium of an un-erupted tooth. Two cases of extremely large and extended follicular cysts related to the upper impacted third molars in young patients and treatments are described. Case 1 Female, aged 16 with swelling of the right cheek and oral vestibule, right exophthalmos and diplopia. Spiral Computed Tomography (CT) showed a massive lesion occupying the maxillary sinus with extension into the pterygo-maxillary space, due to the destruction of the posterior antral bone wall. Above the lesion was compressing the orbital floor. Transantral surgical excision was performed approaching to the pterygo-maxillary space and orbital structure also using the operating microscope. 5-years follow-up shows good restoring of the involved structures without relapse. Case 2 - Female, aged 22, with swelling of the left cheek and oral vestibule, left nasal obstruction, orbital pain and diplopia. Spiral CT-MR integrated study allowed a very accurate analysis: the lesion occupied the entire maxillary sinus, the pterygo-maxillary space, the left nasal cavity, ethmoidal structures with posterior orbital compression. Transantral surgical excision was performed approaching to the pterygo-maxillary space; nasal-ethmoidal and orbital structures were approached by endoscopic technique. Follow-up shows good clinical, anatomical and functional conditions. Histological examination confirmed in both cases the diagnosis of follicular cyst. Giant follicular cysts require an accurate preoperative study due to the delicate structures that may be involved. In the reported cases, the operating microscope and endoscopic surgical procedures were needed in the delicate surgical steps to perform the detachment in deep areas

Optical and magneto-optical properties of ferromagnetic full-Heusler films: experiments and first-principles calculations

We report a joint theoretical and experimental study focused on understanding the optical and magneto-optical properties of Co-based full-Heusler compounds. We show that magneto-optical spectra calculated within ab-initio density functional theory are able to uniquely identify the features of the experimental spectra in terms of spin resolved electronic transitions. As expected for 3d-based magnets, we find that the largest Kerr rotation for these alloys is of the order of 0.3o in polar geometry. In addition, we demonstrate that (i) multilayered structures have to be carefully handled in the theoretical calculations in order to improve the agreement with experiments, and (ii) combined theoretical and experimental investigations constitute a powerful approach to designing new materials for magneto-optical and spin-related applicationsComment: 20 pages, including 6 figures and 1 table. 40 refs. To be published in Phys. Rev.

Recent transmission clustering of HIV-1 C and CRF17_BF strains characterized by NNRTI-related mutations among newly diagnosed men in central Italy

Increased evidence of relevant HIV-1 epidemic transmission in European countries is being reported, with an increased circulation of non-B-subtypes. Here, we present two recent HIV-1 non-B transmission clusters characterized by NNRTI-related amino-acidic mutations among newly diagnosed HIV-1 infected men, living in Rome (Central-Italy)

Preface Special Issue on novel superconducting and magnetic materials

Superconductivity and magnetism -- and their entanglement in a single material -- are among the most studied phenomena in condensed matter physics and continue to pose new challenges for fundamental research and exciting opportunities for technological applications. The last decade has witnessed ground-breaking discoveries in both fields: high-temperature superconductivity in compressed hydrides, unconventional superconductivity in iron-based materials and new types of magnetic states in spin-orbit coupled materials with topological and nematic characteristics. The prediction of material-specific properties and the interpretation of superconducting and magnetic phase transitions have been crucially aided by advances in ab-initio electronic structure methods within the density functional theory and its extensions. This special issue gathers together selected theoretical and experimental contributions on novel aspects of superconductivity and magnetism, %that have been collected in memory of Prof. Sandro Massidda. The collection aims to provide an updated view on timing issues and challenges in this active research field that have been at the hearth of Sandro's scientific interests. As commemorated in the obituary by Continenza and Colombo, Sandro has dedicated his scientific work to the development and application of \textit{ab-initio} computational and theoretical methods, yet never losing focus to the ultimate goal of theoretical and computational physics, that is to support, complement and understand the experimental observations

MgB2 and BeB2: A comparative study of their electronic and superconducting properties

We report a detailed study of the electronic and dynamical properties of superconducting MaB(2) and BeB2. Carefully comparing their band structure at different volumes and the corresponding phonon frequencies for the E-2g mode, we are able to explain their very different superconducting behavior in terms of different electron-phonon coupling. Our calculations are performed within the local-density approximation to the density-functional theory, using the full-potential linearized augmented plane wave and plane-wave pseudopotential in order to calculate phonon frequencies with frozen-phonon approach and linear-response theory, respectively. Our results highlight differences and similarities between the two compounds and give information regarding the zone center E-2g phonon frequencies, electron-phonon coupling, valence-band top deformation potentials at different volumes, and Gruneisen parameters. Our results compare well with available experimental measurements

Electronic, dynamical and superconducting properties of MgB2: doping, surface and pressure effects

We report a detailed first-principles local-density-functional investigation of the structural, electronic, dynamical and superconducting properties of MgB2 focusing on different aspects related to this material. In particular, we examine Al doping, as well as reduced dimensionality and pressure effects on the electronic and superconducting properties of this compound. Our ab initio calculations for the case of 50% Al doping are able to correctly reproduce the measured frequencies of the E-2g phonon and explain the disappearance of superconductivity in terms of filling effects on both carrier concentration and electron-phonon coupling. The surface study shows that an enhanced density of states at the Fermi level is found in the B-terminated case. However, we find the Mg-terminated surface to be the most stable structure in the whole range admitted by the chemical potentials, in agreement with very recent experimental results. Finally, the study of the E-2g phonon frequency under pressure is able to explain the critical temperature lowering under applied pressure

Disorder-induced localisation and suppression of superconductivity in YSr 2 Cu 3 O 6+ x

International audienceBy means of ab initio calculations within the local density approximation to density functional theory, we investigate the electronic structure of the 60 K superconductor YSr 2 Cu 3 O 6+x (YSCO). We focus on the effects of the Sr/Ba substitution and on the main structural modifications induced by this substitution experimentally found in the Sr compound, namely the tetragonal symmetry and the oxygen disorder in the basal plane. In the calculations, this disorder is simulated by using a supercell approach. Due to band structure effects, we find a larger stabilisation free energy of the orthorhombic structure in YBa 2 Cu 3 O 6+x (YBCO). In YSCO, the tetragonal disordered phase is found to be stabilized by oxygen overdoping (x > 1) and by sufficiently large mass-enhancement factors, γ > 5. The analysis of the atomic site projected density of states suggests that oxygen disorder in the CuO basal planes of YSCO induces hole localisation, which accounts for the large 30 K reduction of T c with respect to YBCO