Time-resolved photoresponse studies of ferromagnet/superconductor nano-bilayers and nanostructures

Thesis (Ph. D.)--University of Rochester. Dept. of Physics and Astronomy, 2010.Interactions of superconducting nanostructures with external ultrafast optical radiation represent a very interesting topic in both the framework of nonequilibrium physics and photodetector applications. Heterogeneous proximized ferromagnet/superconductor nano-bilayers are very promising since they exhibit the ultrafast Cooper-pair and quasiparticle dynamics. In this thesis, to study on the role of proximity effect on electron-phonon coupling in F/S heterostructures, we have characterized NiCu/Nb, NiCu/Au/YBaCuO, and LaSrMnO/YBaCuO nano-bilayers, using time-resolved, all optical, femtosecond pump-probe spectroscopy method and transient photoimpedance measurement. We fitted the experimental data with the two-temperature (2-T) model and our own extension model, the three-temperature (3-T) model, which involves relaxation quasiparticles with both optical and acoustic phonons. The 3-T model gives more accurate fitting results than the 2-T model. Moreover, our time-resolved studies of the carrier dynamics in oxide-based F/S structures open the way to novel basic-physics investigations of nonequilibrium effects in correlated systems. Our research results demonstrate that the F/S nanobilayers represent a new class of designed superconducting structures, which can be used in future for ultrafast photodetectors