Spin scatterer and possible Kondo effects near a quantum point contact

Full text: The influence of electron spin on electrical transport measurements in semiconductor nanostructures is presently a subject of great interest. Spin-derived effects in nanostructures, including apparent spin-splitting measurements at zero magnetic field, remain incompletely understood. A proper understanding of spin dynamics is required before correlated electron physics in one dimension can be meaningfully analysed. The novel manifestation of spin based scattering reported here is therefore of great interest. Undoped GaAs/AlGaAs nanostructures have been fabricated to investigate correlation- and spin-related phenomena in one dimension, in systems free of dopant-related disorder. The electron systems in these undoped structures have been demonstrated already to be of unprecedented quality. Quantized conductance structure is observed in quantum point contacts and quantum wires. In a few devices, a strong conductance reduction affecting many conductance plateaux is observed. Strong dependence on thermal cycling indicates that scattering arises at a single site. Furthermore, in-plane magnetic field data imply that the scattering is via a spin- rather than charge-related interaction. Strong spin interactions which can qualitatively alter conductance data are new in point contacts, but have been reported in other nanostructures such as quantum dots. The temperature- and voltage-dependent spin scattering data are reminiscent of recent Kondo effect studies in other semiconductor architectures. In the Kondo effect, an isolated site with a magnetic moment can interact with the spins of current-carrying electrons, providing a new scattering mechanism. In some devices, such spin-flip processes can measurably alter device behaviour. The relevance of the undoped nanostructure results to Kondo physics is therefore of interest. Further measurements in this system are expected to yield new insight into the role of spin in several branches of electron transport studies