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Abstract - In this talk the problem of doping-induced variations in the physical properties of carbon nanotubes is addressed. In particular, transport and magnetic properties are considered. Regarding the transport properties, nanotube-based sensors depend on sizable conductivity changes induced by impurities. Predictions of which impurity/nanotube combination provides good sensor characteristics are usually made on a case-by-case basis, following the study of how a particular nanotube responds to the presence of a specific doping agent. With a multitude of possible combinations, this so-called forward modeling approach is unable to address questions of general nature, like, for instance, the necessary features the components must have to produce certain physical properties on the device. Questions of this nature call for an inverse modeling scheme in which information about the sensor components can be extracted from the knowledge of a few physical quantities demanded for the device. Here we make use of a mathematically transparent formalism that works in both the forward and the inverse directions. We argue that this method can provide general guidelines on the absorption process and is a first step to narrow down the universe of combinations of tube and doping agents capable of producing efficient nano-scale sensors. Regarding the magnetic properties, we are interested in establishing the nature of the indirect coupling that arises when magnetic impurities are present. This coupling is known to play a central role in determining the magnetic order in systems composed of adsorbed magnetic moments in metallic hosts. For low-dimensional metallic structures, such as nanotubes, this interaction is predicted to decay rather slowly. Ab-initio calculations have nevertheless been unable to reproduce this prediction. To clarify this matter, we make use of a simple analytical expression for the indirect coupling that, on the one hand, confirms the long ranged nature of this interaction, and, on the other hand, points to situations in which the coupling may display unexpectedly shorter ranges. We show that the interaction range depends rather sensitively on the location of the magnetic moments, which explains the difficulty in probing the long range character of the indirect coupling from standard ab-initio calculations. Finally, we consider the nature of the magnetic coupling when these impurities are allowed to precess. By calculating the frequency-dependent spin susceptibility we are able to identify resonant peaks whose respective widths provide information about the dynamic aspect of the indirect coupling. We show that by departing from a purely static representation to another in which the moments are allowed to precess, we change from what is already considered a long range interaction to another whose range is far superior. In other words, localized magnetic moments embedded in a metallic structure can feel each other’s presence more easily when they are set in precessional motion. We argue that such an effect may have useful applications leading to large-scale spintronics devices
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