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Spin effects in transport through magnetic nanostructures in the Kondo regime

Final Report Summary - SPINKOND (Spin effects in transport through magnetic nanostructures in the Kondo regime)

The limitations of further miniaturization of present-day electronic circuits stimulate the search for new technologies to store and manipulate information. Spintronics is one of the major new directions that emerged in recent years - it aims at using the additional degree of freedom - the spin - to store and process information. One of the most promising candidates for future spintronic devices is nanostructures such as molecules and quantum dots. However, in order to exploit such devices in spin nanoelectronics, it is crucial to fully understand their behavior and properties. The transport properties of considered nanostructures depend greatly on the quality of contact to external electrodes. When the coupling to the leads is relatively weak, Coulomb blockade and single-electron charging phenomena become relevant. On the other hand, if the coupling is strong and the temperature sufficiently low, the electronic correlations can give rise to the Kondo effect, which manifests itself as maximum conductance through the system.

The main objective of the SPINKOND project was to explore the transport characteristics of quantum dot and molecular structures coupled to external electrodes in the Kondo regime. The considerations involved hybrid nanostructures, such as quantum dots coupled to ferromagnetic and/or superconducting electrodes. Moreover, thermoelectric phenomena in spin-polarized transport through quantum dots and molecules were also addressed. Depending on the ground state of the system and particular device’s setup, there can be different types of the Kondo effect. Within the SPINKOND project the so-called fully-screened, under-screened and over-screened Kondo phenomena were thoroughly investigated. The calculations were mainly performed with the aid of the numerical renormalization group method, which is an essentially exact and very powerful numerical method to study transport through quantum impurity systems coupled to external leads.

The results obtained during the execution of the SPINKOND project were published in 22 papers and presented at 13 conferences. The obtained results are expected to contribute to the general understanding of transport phenomena in various nanostructures exhibiting nontrivial correlations. On one hand, they are expected to stimulate further theoretical and experimental research into the spin-polarized properties of quantum dots and molecules and, on the other hand, to be of assistance in explaining and understanding the current and future experiments on transport through magnetic nanostructures. Since nanoscience and nanotechnology play a crucial role in the development of many different areas, ranging e.g. from information and communication technology to medical therapy, the research project contributes to the general improvement of the well-being and the quality of life of European societies.

Contact: Dr. hab. Ireneusz Weymann ( Mesoscopic Physics Division, Faculty of Physics, Adam Mickiewicz University, Poznan, Poland