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Prof. Dr. Gertrud Zwicknagl, Institut f. Mathemat. Physik, TU Braunschweig – Breaking translational invariance by population imbalance in superconductors: The Fulde-Ferrel-Larkin-Ovchinnikov states – 05 de Agosto 14:00
5 de agosto:14:00 - 15:00
An overview is given of our present understanding of superconductivity with spontaneously broken translation symmetry in polarized Fermi systems. The existence of “crystalline” superconducting phases is considered in a wide range of systems, prominent examples being conduction electrons in metals, ultra-cold atoms in a trap, nuclear matter, and dense quark systems. The underlying physics is delineated and theoretical approaches to the inhomogeneous phases and their properties are discussed. In natural metals, prime candidates for the realization of superconductivity with imbalance-induced order parameters are layered organic compounds and potentially in heavy-fermion systems. Exciting candidates are artificially structured materials. In recent years, the manufacturing of controlled ultra-thin superconducting films has made impressive progress. Important examples are monoatomic or monomolecular layers on a substrate, superconducting layers in a superlattice, or superconducting interfaces and surfaces. These systems have in common the absence of inversion symmetry and hence the presence of Rashba-type spin-orbit energy λ. The latter can be tuned to some extent by varying the thickness, the number of layers, or by applying an electric voltage. The subtle interplay of spin imbalance created by a magnetic field and the Rashba spin-orbit interaction gives rise to novel phenomena in quasi-2D superconductors which, in turn, could provide new functionalities. I discuss the results of a microscopic theory of superconducting films with population imbalance which are subject to Rashba spin-orbit interaction. The full range from small to large spin-orbit interaction is covered. A quantum phase transition at a critical value of the spin-orbit energy λc is predicted where abrupt changes in the superconducting state are expected. It is tempting to speculate, that this feature might give rise to novel phenomena. For example, the Josephson interference effects should change dramatically near this point. These and other open issues together with recent work and promising future directions will be discussed.