9,834 research outputs found
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
Tunneling spectroscopy of the superconducting state of URu2Si2
We present measurements of the superconducting gap of URuSi made with
scanning tunneling microscopy (STM) using a superconducting tip of Al. We find
tunneling conductance curves with a finite value at the Fermi level. The
density of states is V shaped at low energies, and the quasiparticle peaks are
located at values close to the expected superconducting gap from weak coupling
BCS theory. Our results point to rather opened gap structures and gap nodes on
the Fermi surface
Efeitos de diferentes substratos na produção de mudas de alface.
O presente trabalho teve por objetivo testar diferentes tipos de substratos, bem como as mais adequadas proporções entre seus constituintes, para a produção de mudas de alface.bitstream/item/46772/1/COT-1420001.pd
Pressure induced effects on the Fermi surface of superconducting 2H-NbSe
The pressure dependence of the critical temperature and upper critical
field has been measured up to 19 GPa in the layered superconducting
material 2H-NbSe. Relating the behavior of to Fermi surface
parameters, we find that the electron phonon coupling of the 2D Nb 4d derived
bands shows a peak at 5 GPa when the charge density wave (CDW) order is
suppressed. On the other hand, shows a bell shaped curve with a
maximum at 10.5 GPa, well above the pressure for the suppression of the CDW
order. Changes in the band structure produce this shift in the maximum of
, demonstrating that 2H-NbSe shows important differences with
respect to other compounds where has a maximum in the temperature-density
phase diagram shaped by the suppression of another, non-superconducting, ground
state.Comment: 5 pages, 4 figures. Small changes in discussion. Typos correcte
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