Special Seminar by Prof. Sonia Haddad
2. Place: Presentation Room in Samsung Library (2nd floor on the north side)
3. Speaker: Prof. S. Haddad (Faculté des Sciences de Tunis)
4. Title: Inhomogeneous organic superconductors: role of disorder and magnetic field
Several experimental studies in low dimensional organic superconductors have given evidence for a phase segregated state where superconducting coexist with and non superconducting domains. The superconducting properties are found to be strongly dependent on the amount of disorder introduced in the sample regardless its origin. The suppression of the superconducting transition temperature Tc shows clear discrepancy with the result expected from the Abrikosov-Gor’kov law giving the behavior of Tc with impurities. Based on the time dependent Ginzburg-Landau theory, we derive a model to account for the striking feature of Tc in organic superconductors for different types of disorder by considering the segregated texture of the system. We also address the possibility of enhanced upper critical field and Nernst signal in a stack of superconducting slabs alternating with nonsuperconducting domains. This enhancement is ascribed to the superconducting fluctuations which become more important as the dimensionality of the system is reduced. We derive, as a function of the superconducting slab thickness L, the upper critical field Hc2 along the slabs and the Peltier coefficient on which depends the Nernst signal. We show that Hc2 exhibits an upward curvature in the two dimensional (2D) limit where the interplane coherence length ξ is smaller than the superlattice periodicity D = L+d, d being the size of the nonsuperconducting domain. In this limit, Nernst signal is found to be strongly enhanced compared to the 3D case. The results are discussed in connection with experimental observations in quasi-1D organic superconductors and superlattices of high-Tc films.