Superconducting nanobridges under magnetic fields

We report on the study of superconducting nanotips and nanobridges of lead with a Scanning Tunnelling Microscope in tunnel and point contact regimes. We deal with three different structures. A nanotip that remains superconducting under a field of 2 T. For this case we present model calculations of the order parameter, which are in good agreement with the experiments. An asymmetric nanobridge of lead showing a two steps loss of the Andreev excess current due to different heating and dissipation phenomena in each side of the structure. A study of the effect of the thermal fluctuations on the Josephson coupling between the two sides of a superconducting nanobridge submitted to magnetic fields. The different experiments were made under magnetic fields up to twenty five times the volume critical field of lead, and in a temperature range between 0.6 K and 7.2 K.Comment: 17 pages, 7 figure

Topological superconductivity in lead nanowires

Superconductors with an odd number of bands crossing the Fermi energy have topologically protected Andreev states at interfaces, including Majorana states in one dimensional geometries. Superconductivity, a low number of 1D channels, large spin orbit coupling, and a sizeable Zeeman energy, are present in lead nanowires produced by nanoindentation of a Pb tip on a Pb substrate, in magnetic fields higher than the Pb bulk critical field. A number of such devices have been analyzed. In some of them, the dependence of the critical current on magnetic field, and the Multiple Andreev Reflections observed at finite voltages, are compatible with the existence of topological superconductivity

Nominal Wage Rigidities in Mexico: Evidence from Social Security Records

This paper analyses the existence and extent of downward nominal wage rigidities in the Mexican labor market using data from the administrative records of the Mexican Social Security Institute (IMSS). This longitudinal, firm-level dataset allows us to track workers employed with the same firm, observe their wage profiles and calculate the nominal-wage changes they experience over time. Based on the estimated density functions of nominal wage changes and other moments of the distribution, we are able to calculate several standard tests of nominal wage rigidity that have been proposed in the literature. Furthermore, we extend these tests to take into account the presence of minimum wage laws that may affect the distribution of nominal wage changes. The densities and tests calculated using these date are similar to those obtained using administrative data from other countries, and constitute a significant improvement over the measures of nominal wage rigidities obtained from household survey data. We find considerably more wage rigidity than previous estimates obtained for Mexico using data from the National Urban Employment Survey suggest. Furthermore, we find evidence that the extent of nominal wage rigidities has been falling over time. We also document the importance of minimum wages in the Mexican labor market, as evidenced by the large fraction of minimum wage earners and the widespread indexation of wage changes to the minimum wage increases.

Quasar Microlensing: when compact masses mimic smooth matter

The magnification induced by gravitational microlensing is sensitive to the size of a source relative to the Einstein radius, the natural microlensing scale length. This paper investigates the effect of source size in the case where the microlensing masses are distributed with a bimodal mass function, with solar mass stars representing the normal stellar masses, and smaller masses (down to $8.5\times 10^{-5}$M$_\odot$) representing a dark matter component. It is found that there exists a critical regime where the dark matter is initially seen as individual compact masses, but with an increasing source size the compact dark matter acts as a smooth mass component. This study reveals that interpretation of microlensing light curves, especially claims of small mass dark matter lenses embedded in an overall stellar population, must consider the important influence of the size of the source.Comment: 6 pages, to appear in ApJ. As ever, quality of figures reduce