13 research outputs found
Chemical-potential standard for atomic Bose-Einstein condensates
When subject to an external time periodic perturbation of frequency , a
Josephson-coupled two-state Bose-Einstein condensate responds with a constant
chemical potential difference , where is Planck's constant
and is an integer. We propose an experimental procedure to produce
ac-driven atomic Josephson devices that may be used to define a standard of
chemical potential. We investigate how to circumvent some of the specific
problems derived from the present lack of advanced atom circuit technology. We
include the effect of dissipation due to quasiparticles, which is essential to
help the system relax towards the exact Shapiro resonance, and set limits to
the range of values which the various physical quantities must have in order to
achieve a stable and accurate chemical potential difference between the
macroscopic condensates.Comment: 13 pages, 4 figure
Effect of the magnetic field orientation on the modulation period of the critical current of ramp-type Josephson junctions
We have investigated the dependence of the critical current I-C on the value and orientation of an externally applied magnetic field H for interface-engineered YBa2Cu3O7-x ramp-type Josephson junctions. The results are compared with measurements of Nb ramp-type junctions with a PdAu interlayer. The I-C versus H dependences are similar to Fraunhofer patterns and their modulation period changes several orders of magnitude with the orientation of the magnetic field. For both junction types, the dependence of the modulation period on the orientation of the magnetic field can be well described by the change of the relevant projection of the junction area and the influence of flux-focusing. Therefore the features of the I-C(H) curves have to be attributed to the ramp geometry and not to specific properties of the superconducting material. (C) 2001 American Institute of Physics