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

Modeling Hybrid Stars with an SU(3) non-linear sigma model

We study the behavior of hybrid stars using an extended hadronic and quark SU(3) non-linear sigma model. The degrees of freedom change naturally, in this model, from hadrons to quarks as the density/temperature increases. At zero temperature, we reproduce massive neutron stars containing a core of hybrid matter of 2 km for the non-rotating case and 1.18 km and 0.87 km, in the equatorial and polar directions respectively, for stars rotating at the Kepler frequency (physical cases lie in between). The cooling of such stars is also analyzed.Comment: Revised version, references and figures added. Accepted for publication in Physical Review

Quark core impact on hybrid star cooling

In this paper we investigate the thermal evolution of hybrid stars, objects composed of a quark matter core, enveloped by ordinary hadronic matter. Our purpose is to investigate how important are the microscopic properties of the quark core to the thermal evolution of the star. In order to do that we use a simple MIT bag model for the quark core, and a relativistic mean field model for the hadronic envelope. By choosing different values for the microscopic parameters (bag constant, strange quark mass, strong coupling constant) we obtain hybrid stars with different quark core properties. We also consider the possibility of color superconductivity in the quark core. With this simple approach, we have found a set of microscopic parameters that lead to a good agreement with observed cooling neutron stars. Our results can be used to obtain clues regarding the properties of the quark core in hybrid stars, and can be used to refine more sophisticated models for the equation of state of quark matter.Comment: 8 pages, 10 figures. Accepted for publication in Physical Review

Hybrid confinement of optical and mechanical modes in a bullseye optomechanical resonator

Optomechanical cavities have proven to be an exceptional tool to explore fundamental and technological aspects of the interaction between mechanical and optical waves. Such interactions strongly benefit from cavities with large optomechanical coupling, high mechanical and optical quality factors, and mechanical frequencies larger than the optical mode linewidth, the so called resolved sideband limit. Here we demonstrate a novel optomechanical cavity based on a disk with a radial mechanical bandgap. This design confines light and mechanical waves through distinct physical mechanisms which allows for independent control of the mechanical and optical properties. Our device design is not limited by unique material properties and could be easily adapted to allow large optomechanical coupling and high mechanical quality factors with other promising materials. Finally, our demonstration is based on devices fabricated on a commercial silicon photonics facility, demonstrating that our approach can be easily scalable.Comment: 16 pages, 11 figure

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