The Kondo model, which is based on the coupling of conduction electrons with local magnetic impurities, was introduced originally to explain the local minimum in the resistance versus temperature curves of some metals. Nowadays, generalizations of this model give rise to some intriguing phenomena of condensed matter physics such as quantum criticality or the emergence of exotic electronic excitations.
We have explored this physics by implementing a pseudo-magnetic Kondo impurity in a nano-fabricated device: a small metallic island connected to several electronic reservoirs through tunable channels. We measured the conductance through the island versus temperature while tuning the different channels, and achieved a direct visualization of the development of a quantum phase transition: the conductance flows towards universal fixed points while reducing the temperature. We present a quantitative comparison with the theoretical predictions for the critical exponents of the conductance when approaching the two- and three-channel fixed points [1, 2].
PhD thesis work performed at C2N, Marcoussis, under the supervision of Frédéric Pierre and Anne Anthore.
 Z. Iftikhar et al., Nature, 526, 233-236 (2015)
 Z. Iftikhar et al., arXiv :1708.02542