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Observation of SU(4) Kondo effect in coupled quantum dots

Gergely Zarand (University of Budapest)

14.06.2013 at 10:15 


Central to condensed matter physics are quantum impurity models, describing how a local degree of freedom interacts with a continuum. We study experimentally and theoretically a double quantum dot device realization of the SU(4) Kondo model, which describes the maximally symmetric screening of a local four-fold degeneracy. As demonstrated through transport measurements and comparison with detailed numerical renormalization group calculations, this device affords an unprecedented probe and exquisite control over the orbital (charge) and spin physics being studied. By performing detailed numerical and analytical computations, we manage to identify the relevant lines of SU(4) fixed points and demonstrate there the universal SU(4) scaling of the conductance. In a magnetic field, a pure charge Kondo state is demonstrated. We are also able to achieve “pseudospin”-resolved bias spectroscopy, providing intimate access to the interplay of spin and orbital degrees of freedom. A careful comparison of the dI/dV spectra with the numerically computed spectral functions reveals the internal charge and spin excitations of the SU(4) Kondo state.

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