Driving and controlling nanoscale electron correlations

The proposed research project concerns the theoretical description of strongly correlated electron systems confined in low dimensions ranging from quantum dots and quantum wires to organic molecules and clusters of transition metal oxides. The general aim of the project is two-fold: (i) the understanding of correlation effects stemming from the Coulomb interaction in low dimensions; (ii) the search for new routes to manipulate the electronic, magnetic, and transport properties of correlated materials, relevant for technological application. Both aspects stand at the forefront of research in modern theoretical condensed matter physics. In order to achieve this challenging goals the project merges aspects of method development with physical applications. Despite the wide range of physical systems considered, from the methodological point of view the proposed research project takes advantage of a unified many-body formalism, which is able to provide a quantitative description of the electronic structure of both low-dimensional and inhomogeneous systems. In this respect, the dynamical mean-field theory (DMFT) and its extensions allow for a completely non-perturbative treatment of electronic correlations. The underlying diagrammatic many-body formalism allows to compute dynamical correlation functions, which are directly related to experimentally accessible physical quantities. Moreover, the knowledge of two-particle vertex functions also represents a fundamental building block in order to include non-local spatial correlations beyond mean-field, within the dynamical vertex approximation, as it was recently shown by the principal investigator and coworkers in the context of correlated nanostructures. The development of a suitable analytic continuation procedure will grant the access to charge and spin transmission function for a direct comparison with experiments. Finally, within the present project the method will also be extended to the Keldysh contour in order to explore the quantum dynamics and the relaxation toward the steady-state of correlated quantum systems far from equilibrium, as well as the electronic structure and the transport properties of correlated nanostructures in the presence of bias voltage and driving external fields. The flexibility of the proposed approach will allow to investigate the role of electronic correlation in a wide range of physical systems of interest. The applications include the study of both charge and spin correlations in strongly correlated nanostructures. In particular, the principal investigator will explore: (i) the entanglement properties of spatially-separated Cooper pairs in systems of coupled quantum dots in the presence of a superconducting environment; (ii) the possibility of tuning the edge magnetism and the magnetic correlations in graphene nanoflakes by means of carrier doping; (iii) the possibility to manipulate transport properties of fullerenes through static and dynamical distortions.

We established a novel paradigm in the field of nanoelectronics. We demonstrated how to exploit the quantum properties of the electrons to realize next-generation electronic devices. The idea behind it all is that electrons propagate with characteristics which are typical of waves. Waves display properties such as reflection, diffraction, and interference, i.e., the redistribution of the intensity when two waves overlap. Experiments demonstrated that electrons display interference patterns, and thus behave like waves. The realization of an electronic device requires the existence of two states: ON/OFF, depending on whether it allows or denies the transmission of electrons (i.e., the electric current). Under specific conditions, in organic materials, the OFF state can be realized with destructive interference, which completely blocks electronic transmission. Moreover, we suggested to exploit the destructive quantum interference in combination with an internal degree of freedom of the electron, i.e., the spin, which have no classical counterpart. The electron spin exists in two states (polarizations) labeled as up and down, and is at the origin of the magnetic properties of materials. Combining these two properties of quantum electrons it is possible to realize a spin filter, i.e., a device which allows to select one of the two spin polarization with high efficiency, by blocking the transmission of either the up or down channel through destructive interference. This opens a new landscape of possibilities in the field of spintronics, which is based on the interpretation of spin as binary code. For instance, our discovery can be relevant for the realization for memory storage and information technologies.