Hebrew University

Title: Coulomb blockade and non-Fermi-liquid behavior in a double-dot device

Abstract:

The two-channel Kondo effect is a prototype for non-Fermi-liquid behavior in correlated electron systems. It occurs when a spin-1/2 local moment is coupled antiferromagnetically with equal strength to two independent conduction-electron channels that overscreen the moment, and is characterized by anomalous thermodynamic and dynamic properties. While certain ballistic metallic point contacts, two-level systems, and heavy fermion alloys have been argued to display the two-channel Kondo effect, a conclusive experimental observation of this elusive effect remains lacking. In this talk I will discuss a possible realization of the two-channel Kondo effect in a double-dot device, comprised of a large quantum dot, indirectly coupled to a lead via an ultrasmall quantum dot. A line of two-channel fixed points is found as a function of the gate voltages, extending to all regimes of the ultrasmall dot. This critical line separates two distinct Fermi-liquid regimes, which are characterized by different values of the conductance. For an asymmetric dot, spin and charge degrees of freedom are entangled: a continuous transition from a spin to a charge two-channel Kondo effect evolves. The crossover temperature to the two-channel Kondo effect is greatly enhanced away from the local-moment regime, making this exotic effect accessible in realistic quantum-dot devices.