Independent Geometrical Control of Spin and Charge Resistances in Curved Spintronics.

Spintronic devices operating with pure spin currents represent a new paradigm in nanoelectronics, with a higher energy efficiency and lower dissipation as compared to charge currents. This technology, however, will be viable only if the amount of spin current diffusing in a nanochannel can be tuned on demand while guaranteeing electrical compatibility with other device elements, to which it should be integrated in high-density three-dimensional architectures. Here, we address these two crucial milestones and demonstrate that pure spin currents can effectively propagate in metallic nanochannels with a three-dimensional curved geometry. Remarkably, the geometric design of the nanochannels can be used to reach an independent tuning of spin transport and charge transport characteristics. These results laid the foundation for the design of efficient pure spin current-based electronics, which can be integrated in complex three-dimensional architectures.

Edge States and Topological Insulating Phases Generated by Curving a Nanowire with Rashba Spin-Orbit Coupling.

We prove that curvature effects in low-dimensional nanomaterials can promote the generation of topological states of matter by considering the paradigmatic example of quantum wires with Rashba spin-orbit coupling, which are bent in a nanoscale periodic serpentine structure. The effect of the periodic curvature generally results in the appearance of insulating phases with a corresponding novel butterfly spectrum characterized by the formation of finite measure complex regions of forbidden energies. When the Fermi energy lies in the gaps, the system displays localized end states protected by topology. We further show that for certain superstructure periods the system possesses topologically nontrivial insulating phases at half filling. Our results suggest that the local curvature and the topology of the electronic states are inextricably intertwined in geometrically deformed nanomaterials.

Spin-orbital coupling in a triplet superconductor-ferromagnet junction.

We study the interplay of spin and orbital degrees of freedom in a triplet superconductor-ferromagnet junction. Using a self-consistent spatially dependent mean-field theory, we show that increasing the angle between the ferromagnetic moment and the triplet vector order parameter enhances or suppresses the p-wave gap close to the interface, according to whether the gap antinodes are parallel or perpendicular to the boundary, respectively. The associated change in condensation energy establishes an orbitally dependent preferred orientation for the magnetization. When both gap components are present, as in a chiral superconductor, first-order transitions between different moment orientations are observed as a function of the exchange field strength.

Magnetic intragap states and mixed parity pairing at the edge of spin-triplet superconductors.

We show that a spontaneous magnetic moment may appear at the edge of a spin-triplet superconductor if the system allows for pairing in a subdominant channel. To unveil the microscopic mechanism behind such an effect, we combine numerical solution of the Bogoliubov-de Gennes equations for a tight-binding model with nearest-neighbor attraction, and the symmetry based Ginzburg-Landau approach. We find that a potential barrier modulating the electronic density near the edge of the system leads to a nonunitary superconducting state close to the boundary where spin-singlet pairing coexists with the dominant triplet superconducting order. We demonstrate that the spin polarization at the edge appears due to the inhomogeneity of the nonunitary state and originates in the lifting of the spin degeneracy of the Andreev bound states.

Prevalência de alterações do índice tornozelo-braço em indivíduos portadores assintomáticos de doença obstrutiva periférica / Prevalence of ankle-brachial index alteractions in patients with asymptomatic peripheral arterial occlusive disease

Fundamentos: A doença arterial obstrutiva periférica é caracterizada por redução do fluxo sanguíneo para os membros inferiores devido a processo oclusivo nos leitos arteriais. Sua manifestação mais comum é a claudicação intermitente. Objetivos: Avaliar a prevalência de alterações na medida do índica tornozelo-braço (ITB) em indivíduos acima de 55 anos sem sintomas de doença arterial periférica e verificar sua relação com fatores de risco cardiovascular. Métodos: Estudo observacional e transversal. A amostra foi composta de 168 indivíduos com idade superior a 55 anos e residentes em Vassouras-RJ. Foi realizada a medida do ITB através do aparelho de ultrassonografia Doppler e aparelho de pressão aneroide. Utilizou-se entrevista para avaliar fatores de risco cardiovascular e o questionário de claudicação de Edimburgo para definir a presença de claudicação intermitente. Resultados: Dos 161 indivíduos estudados, 102 (63,35%) apresentavam índice entre 0,90-1,30: 45 (27,95%) apresentaram ITM<0,90 sem queixas de claudicação intermitente e 14(8,70%) apresentavam ITB<0,90 e claudicação intermtente como sintoma da doença. Quanto aos fatores de risco nos indivíduos com doençaa arterial obstrutiva periférica, prevaleceu no sexo masculino: hipertensão arterial (64,28%), sedentarismo (57,14%) e dislipidemia (46,42). Já no sexo feminino: sedentarismo (48,38%)...

Is the nature of itinerant ferromagnetism playing a role in the competition between spin polarization and singlet pair correlations?

We consider the competition between spin singlet pairing and itinerant ferromagnetism whose magnetization is yielded by a relative shift of the bands with opposite spin polarization or by asymmetric spin-dependent bandwidths. Within the framework of the exact solution of an extended version of the reduced BCS model, the structure of the coexisting state is shown to have general features that are not related to the character of the ferromagnetism. The role of different types of ferromagnet is then investigated for the proximity effect in a system made of a bilayer junction with a spin singlet superconductor interfaced with a ferromagnet in the clean limit. We show that the qualitative behaviour of the proximity effect does not depend on the nature of the ferromagnetism. Differences emerge at the borderline with the half-metallic regime. For the spin-dependent bandwidth type of ferromagnetism the pairing amplitude exhibits an oscillating behaviour until the density of the minority spin carrier becomes almost zero. The crossover from an oscillating to an exponentially damped profile occurs away from the half-metallic limit when a spin exchange type ferromagnet is considered.

Coexistence of ferromagnetism and singlet superconductivity via kinetic exchange.

We propose a novel mechanism for the coexistence of metallic ferromagnetism and singlet superconductivity assuming that the magnetic instability is due to kinetic exchange. Within this scenario, the unpaired electrons which contribute to the magnetization have a positive feedback on the gain of the kinetic energy in the coexisting phase by undressing the effective mass of the carriers involved in the pairing. The evolution of the magnetization and pairing amplitude and the phase diagram are first analyzed for a generic kinetic exchange model and then are determined within a specific case with spin dependent bond-charge occupation.