Magnetoresistive Effects in Ferromagnet-Superconductor Multilayers

We consider a nanoscale system consisting of Manganite-ferromagnet and Cuprate-superconductor multilayers in a spin valve configuration. The magnetization of the bottom Manganite-ferromagnet is pinned by a Manganite-antiferromagnet. The magnetization of the top Manganite-ferromagnet is coupled to the bottom one via indirect exchange through the superconducting layers. We study the behavior of the critical temperature and the magnetoresistance as a function of an externally applied parallel magnetic field, when the number of Cuprate-superconductor layers are changed. There are two typical behaviors in the case of a few monolayers of the Cuprates: a) For small magnetic fields, the critical temperature and the magnetoresistance change abruptly when the flipping field of the top Manganite-ferromagnet is reached. b) For large magnetic fields, the multilayered system re-enters the zero-resistance (superconducting) state after having become resistive (normal).Comment: 3 pages, 3 figures. 2004 Magnetism and Magnetic Materials Conferenc

Two-band superfluidity from the BCS to the BEC limit

We analyze the evolution of two-band superfluidity from the weak coupling Bardeen-Cooper-Schrieffer (BCS) to the strong coupling Bose-Einstein condensation (BEC) limit. When the interband interaction is tuned from negative to positive values, a quantum phase transition occurs from a 0-phase to a $\pi$-phase state, depending on the relative phase of two order parameters. Furthermore, population imbalances between the two bands can be created by tuning the intraband or interband interactions. We also find two undamped low energy collective excitations corresponding to in-phase and out-of-phase modes. Lastly, we derive the coupled Ginzburg-Landau equations, and show that they reduce to coupled Gross-Pitaevskii equations for two types of bosons in the BEC limit.Comment: 4 pages and 3 figure

BCS-BEC crossover of collective excitations in two-band superfluids

We use the functional integral approach to study low energy collective excitations in a continuum model of neutral two-band superfluids at T=0 for all couplings with a separable pairing interaction. In the long wavelength and low frequency limit, we recover Leggett's analytical results in weak coupling (BCS) for s-wave pairing, and further obtain analytical results in strong coupling (BEC) for both two and three dimensional systems. We also analyse numerically the behavior of the out-of-phase {\it exciton} (finite frequency) mode and the in-phase {\it phonon} (Goldstone) mode from weak to strong coupling limits, including the crossover region. In principle, the evolution of Goldstone and finite frequency modes from weak to strong coupling may be accessible experimentally in the superfluid phase of neutral Fermi atomic gases, and could serve as a test of the validity of the theoretical analysis and approximations proposed here.Comment: 14 pages, 9 figures. Submitted to PR

Validação da BRBN-T: adaptação do Selective Reminding Teste do Word List Generation

Objective: This study aims to present the Selective Reminding Test (SRI) and Word List Generation (WLG) adaptation to the Portuguese population, within the validation of the Brief Repeatable Battery of Neuropsychological Tests (BRBN-T) for multiple sclerosis .(MS) patients. Method: 66 healthy participants (54.5% female) recruited from the community volunteered to participate in this study. Results: A combination of procedures from Classical Test Theory (OTT) and Item Response Theory (ITR) were applied to item analysis and selection. For each SRT list, 12 words were selected and 3 letters were chosen for WLG to constitute the final versions of these tests for the Portuguese population. Conclusion: The combination of CTT and ITR maximized the decision making process in the adaptation of the SRI and WLG to a different culture and language (Portuguese). The relevance of this study lies on the production of reliable standardized neuropsychological tests, so that they can be used to facilitate a more rigorous monitoring of the evolution of MS, as well as any therapeutic effects and cognitive rehabilitation.info:eu-repo/semantics/publishedVersio

Psychological and social factors in rheumatic diseases

Rheumatic diseases are major causes of different degrees of pain, disability and deformity. They have strong impact in patient’s lives, especially in psychological and social dimensions, as a result of their healthcare needs. The present study has a qualitative nature and is based on the evaluation of the impact of changes related to the progression of rheumatic diseases and on how the disease affects patients, namely at psychological, professional and social level. We conducted a focus-group to understand how illness could limit the daily life of these adult patients, women and men, with rheumatic diseases. Along the analysis and discussion of the results, we found out that the patients with rheumatic diseases have a health condition extremely complex, particularly in a psychological and emotional dimension. They have suffered severe changes, associated to emotional disturbances, related with demotivation, anxiety, nervousness, and physical limitations of multiple sorts, which lead to frustration or dissatisfaction. The rheumatic diseases can strongly affect the profession and social activity of the patients, but the family and friends support was proven to have a positive impact in the individuals, softening some negative effects of the illness. Our study emphasizes that it is recommended that nurse practitioners participate in the evaluation of these patients, in order to provide the adequate healthcare that they require, and aiming to promote their wellbeing.info:eu-repo/semantics/acceptedVersio

Generation of Superposition States and Charge-Qubit Relaxation Probing in a Circuit

We demonstrate how a superposition of coherent states can be generated for a microwave field inside a coplanar transmission line coupled to a single superconducting charge qubit, with the addition of a single classical magnetic pulse for chirping of the qubit transition frequency. We show how the qubit dephasing induces decoherence on the field superposition state, and how it can be probed by the qubit charge detection. The character of the charge qubit relaxation process itself is imprinted in the field state decoherence profile.Comment: 6 pages, 4 figure

Phase Fluctuations and Vortex Lattice Melting in Triplet Quasi-One-Dimensional Superconductors at High Magnetic Fields

Assuming that the order parameter corresponds to an equal spin triplet pairing symmetry state, we calculate the effect of phase fluctuations in quasi-one-dimensional superconductors at high magnetic fields applied along the y (b') axis. We show that phase fluctuations can destroy the theoretically predicted triplet reentrant superconducting state, and that they are responsible for melting the magnetic field induced Josephson vortex lattice above a magnetic field dependent melting temperature Tm.Comment: 4 pages (double column), 1 eps figur

Two-species fermion mixtures with population imbalance

We analyze the phase diagram of uniform superfluidity for two-species fermion mixtures from the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensation (BEC) limit as a function of the scattering parameter and population imbalance. We find at zero temperature that the phase diagram of population imbalance versus scattering parameter is asymmetric for unequal masses, having a larger stability region for uniform superfluidity when the lighter fermions are in excess. In addition, we find topological quantum phase transitions associated with the disappearance or appearance of momentum space regions of zero quasiparticle energies. Lastly, near the critical temperature, we derive the Ginzburg-Landau equation, and show that it describes a dilute mixture of composite bosons and unpaired fermions in the BEC limit.Comment: 4 pages with 3 figures, accepted version to PR