"Hybrid ferromagnetic-superconductor nanosystems"
Prof. Sergei P. Kruchinin

物理学会北海道支部講演会（第204回エンレイソウの会との共催）

講演題目：　Hybrid ferromagnetic-superconductor nanosystems
講　師　：　Prof. Sergei P. Kruchinin
　　　　　Bogolyubov Institute for Theoretical Physics, Ukraine
日　時　：　平成26年10月16日 (火) 16:30-18:00
場　所　：　北海道大学工学部A棟A1-17

要　旨　：
Recent advances in nanoscience have demonstrated that fundamentally new physical phenomena are found, when systems are reduced in size to dimensions that become comparable to the fundamental microscopic length scales of a material under study. Superconductivity is a macroscopic quantum phenomenon, and therefore it is of particular interest to see how this quantum state is influenced when the samples are reduced to nanometer sizes. Nowadays, developments in nanotechnologies and measurement techniques allow the experimental investigation of the magnetic and thermodynamic superconducting properties of mesoscopic samples in this regime. In this lecture, we will present theoretical models to describe such nanoscale superconducting systems and discuss possible new experimental phenomena we can predict within these theoretical models. We will consider the theory of interactions between two nanoscale ferromagnetic particles embedded in a superconductor. In the London limit approximation, we show that the interactions between ferromagnetic particles can lead to either parallel or antiparallel spin alignment. The crossover between those is dependent on the ratio of the interparticle spacing and the London penetration depth. We will show that a phase transition between spin orientations can occur as the temperature is varied. Finally, we comment on the extension of these results to arrays of nanoparticles in different geometries. In view of modern experimental data, we consider also composite nanowires made from both superconducting and ferromagnetic metals in the case of cylindrical geometry, where one metal forms the core of a nanowire, and the second forms an outer cylindrical sheath. Moreover, we analyze also the inverse situation, in which a normal or ferromagnetic core is surrounded by a superconducting sheath. In this case, it is interesting to examine the spectrum of Andreev bound states in the normal or ferromagnetic core.

世話人　 浅野 泰寛
（asano@eng.hokudai.ac.jp）
北海道大学大学院工学研究院応用物理学部門

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