STM study of multiband superconductivity in NbSe2 using a superconducting tip

We present a method to produce superconducting tips to be used in Scanning Tunneling Microscopy/Spectroscopy experiments. We use these tips to investigate the evolution of the electronic density of states of NbSe2 from 0.3K up to its critical temperature (7.2K). The use of a superconducting tip (Pb) as ounterelectrode provides an enhancement of the different features related to the DOS of NbSe2 in the tunneling conductance curves, along all the studied thermal range. The analysis of the experimental results gives evidence of the presence of multiband superconductivity in NbSe2.Comment: 5 pages, 5 figures, PDF fil

Towards linking freshwater plants and ecosystems via functional biogeography

Functional biogeography has advanced the field of functional ecology into a more spatiallypredictive science. However, freshwater plants are still underrepresented in these traitbased advancements. Here, we argue that there is a need for developing a functional biogeographical framework for freshwater plants and initiate global mapping efforts focusing on the form and function of freshwater plants. Specific attention should be given to (1) the placement of freshwater plants in the global plant trait space and show how this placement links to global traitenvironment relationships; (2) the theoretical framework for major structural traittrait correlations based on the physical constraints in aquatic ecosystems; (3) the evolutionary and environmental drivers underlying the global distribution of inter and intraspecific variation in different life forms; and (4) the level of equilibrium between spatial and temporal traitenvironment relationships in freshwater plants. By putting freshwater plants in the context of these spatial aspects, we could advance our understanding of freshwater plant adaptations and responses to environmental gradients, and thereby facilitate predicting the consequences of global changes for freshwater ecosystem functions and services.Environmental Biolog

Proximity effect and strong coupling superconductivity in nanostructures built with an STM

We present high resolution tunneling spectroscopy data at very low temperatures on superconducting nanostructures of lead built with an STM. By applying magnetic fields, superconductivity is restricted to length scales of the order of the coherence length. We measure the tunneling conductance and analyze the phonon structure and the low energy DOS. We demonstrate the influence of the geometry of the system on the magnetic field dependence of the tunneling density of states, which is gapless in a large range of fields. The behavior of the features in the tunneling conductance associated to phonon modes are explained within current models.Comment: 4 figures, 4 page

Two qubits of a W state violate Bell's inequality beyond Cirel'son's bound

It is shown that the correlations between two qubits selected from a trio prepared in a W state violate the Clauser-Horne-Shimony-Holt inequality more than the correlations between two qubits in any quantum state. Such a violation beyond Cirel'son's bound is smaller than the one achieved by two qubits selected from a trio in a Greenberger-Horne-Zeilinger state [A. Cabello, Phys. Rev. Lett. 88, 060403 (2002)]. However, it has the advantage that all local observers can know from their own measurements whether their qubits belongs or not to the selected pair.Comment: REVTeX4, 5 page

Connecting Numerical Relativity and Data Analysis of Gravitational Wave Detectors

Gravitational waves deliver information in exquisite detail about astrophysical phenomena, among them the collision of two black holes, a system completely invisible to the eyes of electromagnetic telescopes. Models that predict gravitational wave signals from likely sources are crucial for the success of this endeavor. Modeling binary black hole sources of gravitational radiation requires solving the Eintein equations of General Relativity using powerful computer hardware and sophisticated numerical algorithms. This proceeding presents where we are in understanding ground-based gravitational waves resulting from the merger of black holes and the implications of these sources for the advent of gravitational-wave astronomy.Comment: Appeared in the Proceedings of 2014 Sant Cugat Forum on Astrophysics. Astrophysics and Space Science Proceedings, ed. C.Sopuerta (Berlin: Springer-Verlag

Balancing the popularity bias of object similarities for personalised recommendation

Network-based similarity measures have found wide applications in recommendation algorithms and made signicant contributions for uncovering users' potential interests. However, existing measures are generally biased in terms of popularity, that the popular objects tend to have more common neighbours with others and thus are considered more similar to others. Such popularity bias of similarity quantification will result in the biased recommendations, with either poor accuracy or poor diversity. Based on the bipartite network modelling of the user-object interactions, this paper firstly calculates the expected number of common neighbours of two objects with given popularities in random networks. A Balanced Common Neighbour similarity index is accordingly developed by removing the random-driven common neighbours, estimated as the expected number, from the total number. Recommendation experiments in three data sets show that balancing the popularity bias in a certain degree can significantly improve the recommendations' accuracy and diversity simultaneously

Scanning microscopies of superconductors at very low temperatures

We discuss basics of scanning tunneling microscopy and spectroscopy (STM/S) of the superconducting state with normal and superconducting tips. We present a new method to measure the local variations in the Andreev reflection amplitude between a superconducting tip and the sample. This method is termed Scanning Andreev Reflection Spectroscopy (SAS). We also briefly discuss vortex imaging with STM/S under an applied current through the sample, and show the vortex lattice as a function of the angle between the magnetic field and sample's surface

Greenberger-Horne-Zeilinger paradoxes for N quNits

In this paper we show the series of Greenberger-Horne-Zeilinger paradoxes for N maximally entangled N-dimensional quantum systems.Comment: 6 page

Upper critical field Hc2H_{c2} calculations for the high critical temperature superconductors considering inhomogeneities

We perform calculations to obtain the $H_{c2}$ curve of high temperature superconductors (HTSC). We consider explicitly the fact that the HTSC possess intrinsic inhomogeneities by taking into account a non uniform charge density $\rho(r)$. The transition to a coherent superconducting phase at a critical temperature $T_c$ corresponds to a percolation threshold among different superconducting regions, each one characterized by a given $T_c(\rho(r))$. Within this model we calculate the upper critical field $H_{c2}$ by means of an average linearized Ginzburg-Landau (GL) equation to take into account the distribution of local superconducting temperatures $T_c(\rho(r))$. This approach explains some of the anomalies associated with $H_{c2}$ and why several properties like the Meissner and Nernst effects are detected at temperatures much higher than $T_c$.Comment: Latex text, add reference

Investigation of stimulated dynamics in strongly anisotropic high-temperature superconductors system Bi-Pb-Sr-Ca-Cu-O

It is used the mechanical method of Abrikosov vortex stimulated dynamics investigation in superconductors. With its help it was studied relaxation phenomena in vortex matter of high-temperature superconductors. It established that pulsed magnetic fields change the course of relaxation processes taking place in vortex matter. The study of the influence of magnetic pulses differing by their durations and amplitudes on vortex system of strongly anisotropic high-temperature superconductors system Bi1.7Pb0.3Sr2Ca2Cu3O10-d showed the presence of threshold phenomena. The small duration pulses do not change the course of relaxation processes taking place in vortex matter. When the duration of pulses exceeds some critical value (threshold), then their influence change the course of relaxation process which is revealed by stepwise change of relaxing mechanical moment.. These investigation showed that the time for formatting of Abrikosov vortex lattice in Bi1.7Pb0.3Sr2Ca2Cu3O10-d is of the order of 150 us which on the order of value exceeds the time necessary for formation of a single vortex observed in isotropic high-temperature superconductor HoBa2Cu3O7-d and on two orders exceeds the creation time of a single vortex observed in classical type II superconductors.Comment: 6 pages, 0 figure