  A system consisting of two independently contacted quantum dots with strong
electrostatic interaction shows interdot Coulomb blockade when the dots are
weakly tunnel coupled to their leads. It is studied experimentally how the
blockade can be overcome by correlated tunneling when tunnel coupling to the
leads increases. The experimental results are compared with numerical
renormalization group calculations using predefined (measured) parameters. Our
results indicate Kondo correlations due to the electrostatic interaction in
this double quantum dot system.
