Lattice configurations and magnetic oscillations in stacks of Josephson junctions
We studied static lattice structures and magnetic oscillations of the critical current in stacks of intrinsic Josephson junctions, which are realized in mesas fabricated from layered high-temperature superconductors. The oscillation behavior is very different from the case of a single junction. Depending on the stack lateral size, oscillations may have either the period of half flux quantum per junction (wide-stack regime) or one flux quantum per junction (narrow-stack regime). We study the crossover between these two regimes. Typical size separating the regimes is proportional to magnetic field meaning that the crossover can be driven by the magnetic field. In the narrow-stack regime the lattice structure experiences periodic series of phase transitions between aligned rectangular configuration and triangular configuration. Triangular configurations in this regime is realized only in narrow regions near magnetic-field values corresponding to integer number of flux quanta per junction.


Figure: Example of oscillating dependences of the critical current on the magnetic field (red line) for different lateral sizes of the mesas. Filled regions show locations of the rectangular lattice.

 

Figure: Size-magnetic field phase diagram of the Josephson-junction stack. Black lines correspond to integer flux quanta per junction. Cyan areas within red curves correspond to regions of rectangular-lattice ground state. Patterns of the oscillating Josephson current in two neighboring layers are illustrated for two points. Red points mark centers of Josephson vortices.

For more details see Phys. Rev. B, 75 (2007) 214513., and talk (use Internet Explorer !)