  We report measurements of the Kondo effect in a double quantum dot (DQD),
where the orbital states act as pseudospin states whose degeneracy contributes
to Kondo screening. Standard transport spectroscopy as a function of the bias
voltage on both dots shows a zero-bias peak in conductance, analogous to that
observed for spin Kondo in single dots. Breaking the orbital degeneracy splits
the Kondo resonance in the tunneling density of states above and below the
Fermi energy of the leads, with the resonances having different pseudospin
character. Using pseudospin-resolved spectroscopy, we demonstrate the
pseudospin character by observing a Kondo peak at only one sign of the bias
voltage. We show that even when the pseudospin states have very different
tunnel rates to the leads, a Kondo temperature can be consistently defined for
the DQD system.
