Influence of the passive region on zero field steps for 
window junctions


A. Benabdallah*, J. G. Caputo+ and N. Flytzanis#

*Max Planck Institute
 for the Physics of Complex Systems
 Noethnitzer Str. 38
 D-01187 Dresden, Germany

+ Laboratoire de Physique Mathematique
  Universite Montpellier II
  34095 Montpellier cedex, France

#Department of Physics
University of Crete
Heraklio, Greece

Modern Josephson junctions due to their process of
fabrication are surrounded by a passive (linear)
region where the thickness of the oxide layer prevents
the passage of the supercurrent. This protects the
oxide layer from degradations due to the environment
and provides an electromagnetic cavity to enhance the
power of the device.
We present a numerical and analytic study of the influence
of the passive region on fluxon dynamics where we examine
the effect of the extension of the passive region and its 
electromagnetic characteristics, its surface inductance
$L_I$ and capacitance $C_I$. 
When the velocity in the passive region $v_s$ is equal to the
Swihart velocity (1) a one dimensional model describes well
the operation of the device. When $v_s$ is different from
1, the fluxon adapts its velocity to $v_s$. In both cases
we give simple formulas for the position of the limiting
voltage of the zero field steps. Large values of 
$L_I$ and $C_I$ lead to different types of solutions which 
are analysed.