In this talk, I will discuss recent measurements in which we investigate spin blockade and Kondo physics in carbon nanotube double quantum dots. Spin blockade is observed in weakly coupled double quantum dots when electron transitions between the dots are forbidden by spin conservation. As such, this phenomenon is of considerable importance in spin-based quantum information processing schemes as a way to convert the spin degree of freedom to a much easier detectable charge state or current. Here I discuss results on spin blockade in carbon nanotube double quantum dots and coupling to impurity spins in the nanotube environment.
The ability to control the tunnel couplings in the nanotube devices also allows us to investigate carbon nanotube double quantum dots which are much more strongly coupled to their leads. In this case, we observe pronounced Kondo features. Of particular interest here is the competition between Kondo correlations and exchange coupling between the spins, when both quantum dots contain an odd number of electrons. These effects have been studied as a function of tunnel coupling, temperature and magnetic field and will be discussed during the second part of the talk, as well as recent radio-frequency reflectometry measurements on the nanotube double quantum dots.