Dynamics and transport in strongly interacting disordered materials
Final Report Abstract
Our findings cover new results on quantum wires, disordered Bose systems and magneto-superconducting hybrid systems. The studies of quantum wires are relevant for understanding transport of charge and spin (spintronic) in those systems and may influence the construction of new nanodevices. We focused on realistic cases when transport is influenced by imperfections (such as external impurities or constrictions), the role of interaction with gates (i.e. other parts of a nanodevice) and external magnetic field. While the reduction of the conductance by imperfections may be avoided under certain conditions (resonance), the interaction with gates (causing dissipation) spoils this effect and leads to an exponential suppression of the current. For systems with two impurities in external magnetic fields (but in the absence of dissipation) we found that the resonance condition depends on the spin projection and allows to produce a spin polarized current and hence act as a spin valve. This observation may have implications for the field of spintronics. The study of Bose-Einstein condensates in disordered media is a recent new direction in the physics of cold atoms but relevant as well for superconductors and superfluids in random media. Our theory of disordered Bose systems exposed in describes nontrivial many-body effects due to the interplay between interaction and disorder. New technological achievements made it possible to produce magneto superconducting hybrid systems under the full control of their parameters. Therefore, it is desirable to predict and explain different phenomena that may occur in such systems. We calculated the resulting magnetic field of a superconductor when a single nanomagnet is placed on top of it. We predicted that many weakly magnetized dots placed on the superconducting film do not change the superconducting phase and found the critical magnetization strength which destroys it. One of our initial aims of the research proposal was to study transport phenomena in quantum wires exposed to magnetic fields. Recent results by other researchers showed that the interaction of the system with its environment can affect the transport by generating dissipation. Taking this as a starting point, we developed a more realistic theory for the charge transport in quantum wires in various cases when the system contains impurities. A second unexpected achievement of the project were the results obtained for dirty Bose sytems, motivated by the recent rapid experimental development on cold atoms and dirty superconductors.
Publications
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"Absence of the Mott Glass Phase in ID Disordered Fermionic Systems" ,Phys. Rev. Lett. 99, 186402 (2007)
T. Nattermann, A. Petkovic, Z. Ristivojevic, and F. Schütze
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"Bose-Einstein Condensates in Strongly Disordered Traps",Phys. Rev. Lett. 100, 060402 (2008)
T. Nattermann and V. L. Pokrovsky
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"Transport in a Dissipative Luttinger Liquid",Phys. Rev. Lett. 101, 016405 (2008). Also in Vir. J. Nan. Sci. Tech. 18, 13 (2008)
Z. Ristivojevic and T. Nattermann
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"Ground state configurations of vortices in a superconducting film with a magnetic dot",Phys. Rev. B (2009)
Z. Ristivojevic
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"Interaction-Localization Paradigm: Bose Gas in a Random Environment" ,Advances in Theoretical Physics, Ed. by V. Lebedev and M. Feigel'man, AIP Conference Proceedings 1134 (2009)
V. L. Pokrovsky, G. M. Falco, and T. Nattermann
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"Localized states and interaction-induced delocalization in Bose gases with quenched disorder",Europhys. Lett. 85, 30002 (2009)
G. M. Falco, T. Nattermann, and V. L. Pokrovsky
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"Order and transport- in interacting disordered low-dimensional systems" ,PhD thesis, University of Cologne (2009)
Z. Ristivojevic
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"Superconducting film with randomly magnetized dots: a realization of the 2D XY model with random phase shifts" ,Phys. Rev. B (2009)
Z. Ristivojevic
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"Transport in a Luttinger liquid with dissipation: two impurities",Phys. Rev. B (2009)
L. Chen, Z. Ristivojevic, and T. Nattermann
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"Weakly interacting Bose gas in a random enviromnent", Phys. Rev. B (2009)
G. M. Falco, T. Nattermann, and V. L. Pokrovsky
