Crossover between 0.7-anomaly and Kondo effect - theory, transport measurements and all-optical spin detection

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Recent theoretical progress from the vDelft group shows (in accord with a scenario due to Y Meir) that the 0.7- anomaly in the conductance of a quantum point contact (QPC) has the same microscopic origin as the Kondo effect for a quantum dot (QD): both arise from a subtle interplay of spin and interaction effects that cause an enhanced local spin susceptibility in the vicinity of low electron density in the QPC or QD. We propose to conduct an in-depth study of the relation between these two phenomena by combining the expertise of three groups: (I) Theory (vDelft): Studying a one-dimensional Hubbard model to describe the QPC-QD crossover, we will generalize our functional renormalization group calculations to finite temperatures and source-drain voltages; we will also aim to model realistically the QPC/QD confinement potentials. (II) Transport experiments (Ludwig): We will fabricate samples and study them, using transport spectroscopy to conduct precise experimental tests of theoretical predictions; thoroughly characterized samples will then be used for optical spin detection, (ill) Optical spin detection (Högele): We will extend our optical spin detection technique with ^m spatial resolution for operation at sub-Kelvin temperatures, and use it to measure local spin polarization in our lateral defined QDs and QPCs. By this unique combination of methods we plan not only to conclusively unravel the microscopic origin of the 0.7-anomaly but also to establish a new technique for optical spin detection whose potential impact in the field of spintronics goes far beyond the scope of the present proposal.