Evidence of quantum phase transition in double charge Kondo quantum dots

The Kondo effect is one of the simplest many body phenomena, in which a single magnetic impurity couples to a continuum of states. Adding a second impurity coupled to the first has been suggested to provide insight into heavy fermion systems. Implementing such impurities in nanofabricated systems with tunable parameters has proven to be a powerful way to compare experiments to theoretical predictions. Recent experimental work demonstrated a new way to realize this type of physics: the charge on a hybrid metal-semiconductor quantum dot coupled to a quantum hall edge state acts as a pseudospin [1]. We build off this design to create a two impurity configuration, with a competition between a dot-dot Kondo interaction and a dot-lead Kondo interaction. We believe this yields a novel quantum critical state. In our device, we controllably tune the various interaction strengths to explore the distinct phases. We provide evidence of a phase transition via transport measurements, with an enhanced conductance when the interaction strengths are comparable.

[1] Iftikhar, Z., et al. Nature, 526(7572), 233–236. (2015)