Point Contact Study of the Superconducting Order Parameter in RuSr2GdCu2O8

We have performed a detailed study of the conductance characteristics obtained by point contact junctions realized between a normal Pt/Ir tip and syntered RuSr2GdCu2O8 (Ru-1212) samples. Indeed, this compound is subject of great interest due to the coexistence of both magnetic order and bulk superconductivity. In our experiments, the low temperature tunneling spectra reproducibly show a zero bias conductance peak that can be well reproduced by a generalized BTK model in the case of d-wave symmetry of the superconducting order parameter.Comment: 3 pages, 2 figures, IJMPB style. Presented at New3SC5 Conference, China, June 200

Point-Contact Spectroscopy on RuSr2GdCu2O8

We present Point-Contact experiments on polycrystalline RuSr$_2$GdCu$_2$O$_8$ samples. The majority of tunneling curves shows a zero-bias conductance peak, which is modeled by assuming a d-wave pairing symmetry of the superconducting order parameter.The magnetic field dependence of the conductance spectra has been measured in very stable junctions. In some cases, due to the granularity of the samples, clusters of grains in series introduce peculiar features in the conductance spectra.Comment: 4 pages, 4 figures, published on Journal of Physics and Chemistry of Solid

Role of Inter-Electron Interaction in the Pseudo-Gap Opening in High T c_c Tunneling Experiments

The analysis of tunneling experiments showing the pseudogap type behavior is carried out based on the idea of the renormalization of density of states due to the inter-electron interaction in the Cooper channel (superconducting fluctuations contribution in tunneling current). It is demonstrated that the observed kink of the zero-bias conductance $G(0,T)$ of $YBaCuO/Pb$ junctions in the vicinity of $T_c$ can be explained in terms of fluctuation theory in a quite wide range of temperature above $T_c$, using the values of microscopic parameters of the $YBaCuO$ electron spectrum taken from independent experiments. The approach proposed also permits to explain qualitatively the shape of the tunneling anomalies in $G(V,T)$ and gives a correct estimate for the pseudogap position and amplitude observed in the experiments on $BiSrCaCuO$ junctions.Comment: 5 pages, 3 figure

Subharmonic gap structures and Josephson effect in MgB2/Nb micro-constrictions

Superconducting micro-constrictions between Nb tips and high quality MgB$_{2}$ pellets have been realized by means of a point-contact inset, driven by a micrometric screw. Measurements of the current-voltage characteristics and of the dynamical conductance versus bias have been performed in the temperature range between 4.2 K and 500 K. Above the Nb critical temperature T$_{C}^{Nb}$, the conductance of the MgB$_2$/normal-metal constrictions behaves as predicted by the BTK model for low resistance contacts while high resistance junctions show quasiparticle tunneling characteristics. Consistently, from the whole set of data we infer the value $\Delta_{\pi} = 2.5 \pm 0.2$ meV for the three-dimensional gap of MgB$_2$. Below T$_{C}^{Nb}$, low resistance contacts show Josephson current and subharmonic gap structures (SGS), due to multiple Andreev reflections. Simultaneous observations of both features, unambiguously indicate coupling of the 3D band of MgB$_2$ with the Nb superconducting order parameter. We found that the temperature dependence of the Josephson critical current follows the classical Ambegaokar-Baratoff behavior with a value $I_CR_N=(2.1 \pm 0.1)$ meV at low temperatures.Comment: 8 pages, 5 figures. Replaced with published versio

Reestruturação do quadro de pessoal de enfermagem e seu impacto sobre as horas de assistência

This descriptive study aimed to calculate and compare the nursing staff at the medical-surgical clinical units of a philanthropic hospital in current and projected situations, and to investigate how much time the nursing team delivers patient care in the current and projected situations. Gaidzinski's method was used to calculate the nursing staff, and the equation proposed by the Hospital Quality Commitment (HQC) to estimate care hours. The findings showed an increase of 33% in the staff, with a 68.4% increase in the number of nurses and 15.6% in the number of technicians / nursing auxiliaries. According to the projected situation, the care hours varied from 5.7 to 7.2. The number of nursing and the mean care time provided to the patients were inadequate according to the clientele's care needs. This could impair the quality of care.Este estudio descriptivo tuvo por objetivo dimensionar y comparar el cuadro de personal de enfermería de las unidades de clínica médico-quirúrgica de un hospital filantrópico, en las situaciones actuales y proyectadas, e investigar el tiempo de asistencia utilizado en los pacientes por el equipo de enfermería en las dos situaciones. Para dimensionar se utilizó el método propuesto por Gaidzinski, y, para el cálculo de las horas de asistencia, la ecuación propuesta por el Compromiso con la Calidad Hospitalaria (CCH). Lo encontrado colocó en evidencia la necesidad de aumentar en 33% el cuadro de personal, con aumento de 68,4% de enfermeros y de 15,6% en el número de técnicos/auxiliares de enfermería. En la situación proyectada, las horas de asistencia variaron de 5,7 a 7,2. El cuantitativo de enfermería y el tiempo promedio utilizado con los pacientes se revelaron inadecuados para atender las necesidades de la clientela, lo que puede comprometer la calidad de la asistencia.Este estudo descritivo objetivou dimensionar e comparar o quadro de pessoal de enfermagem das unidades de clínica médico-cirúrgica de um hospital filantrópico, nas situações atuais e projetadas, e investigar o tempo de assistência dispensado aos pacientes pela equipe de enfermagem nas duas situações. Utilizou-se, para o dimensionamento, o método proposto por Gaidzinski, e, para o cálculo das horas de assistência, a equação proposta pelo Compromisso com a Qualidade Hospitalar (CQH). Os achados evidenciaram necessidade de acréscimo de 33% no quadro de pessoal, com aumento de 68,4% de enfermeiros e de 15,6% no número de técnicos/auxiliares de enfermagem. Na situação projetada, as horas de assistência variaram de 5,7 a 7,2. O quantitativo de enfermagem e o tempo médio dispensado aos pacientes revelaram-se inadequados às necessidades de atendimento da clientela, podendo comprometer a qualidade da assistência

Point Contact Spectra on YBa2_2Cu3_3O7−x_{7-x}/La0.7_{0.7}Ca0.3_{0.3}MnO3_3 bilayers

We present conductance characteristics of point contact junctions realized between a normal Pt-Ir tip and YBa$_2$Cu$_3$O$_{7-x}$/La$_{0.7}$Ca$_{0.3}$MnO$_3$ (YBCO/LCMO) bilayers. The point contact characteristics show a zero bias conductance peak, as a consequence of the formation of Andreev bound states at the YBCO Fermi level. The temperature evolution of the spectra reveals a depressed zero bias peak and a reduced superconducting energy gap, both explainable in terms of spin polarization effects due to the LCMO layer.Comment: 4 pages, 4 EPS figures. Proceedings of EUCAS 2005. Accepted in Journal of Physics: Conference Serie

Pairing state in the rutheno-cuprate superconductor RuSr2GdCu2O8: A point contact Andreev Reflection Spectroscopy study

The results of Point Contact Andreev Reflection Spectroscopy on polycrystalline RuSr$_2$GdCu$_2$O$_8$ pellets are presented. The wide variety of the measured spectra are all explained in terms of a modified BTK model considering a \emph{d-wave} symmetry of the superconducting order parameter. Remarkably low values of the energy gap $\Delta=(2.8\pm 0.2)meV$ and of the $2\Delta/k_BT_c\simeq 2$ ratio are inferred. From the temperature evolution of the $dI/dV$ vs $V$ characteristics we extract a sublinear temperature dependence of the superconducting energy gap. The magnetic field dependence of the conductance spectra at low temperatures is also reported. From the $\Delta$ vs $H$ evolution, a critical magnetic field $H_{c_2}\simeq 30 T$ is inferred. To properly explain the curves showing gap-like features at higher voltages, we consider the formation of a Josephson junction in series with the Point Contact junction, as a consequence of the granularity of the sample.Comment: 8 pages, 7 EPS figures. Accepted in Phys. Rev.