  A triangular triple quantum dot gives various Kondo effects, such as the
emergence of an electric polarization accompanied by a complete compensation of
spin degrees of freedom. The interplay of spin and charge of electrons in
quantum dots is investigated using an Anderson model with an equilateral
triangular spin cluster, in which a single electron state at one site is
hybridized with a conduction band in a lead. The numerical renormalization
group analysis shows how a nonzero electric polarization develops with local
electrons traveling in the loop and how it depends on the hybridization
strength as an experimentally controllable parameter in the Kondo effect.
