University of Minnesota
School of Physics & Astronomy
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Oriol T. Valls

Supra-oscillatory critical temperature dependence of Nb-Ho bilayers
F. Chiodi, J.D.S. Witt, R.G.J. Smits, L. Qu, G.B. Halasz, C-T Wu, O.T. Valls, K. Halterman, J.W.A. Robinson, M.G. Blamire, Europhys. Lett., 101, 37002 (2013)

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We investigate the critical temperature, $T_c$, of a thin s-wave superconductor (Nb) proximity coupled to a helical rare earth ferromagnet (Ho). As a function of the Ho layer thickness, we observe multiple oscillations of $T_c$, superimposed on a slow decay with a characteristic length of $\sim$40 nm. We fit our experimental results with the self consistent Bogoliubov-de Gennes equations, including both singlet and triplet pair correlations, and obtain a good agreement. We also observe non-trivial transitions into the superconducting state, the zero resistance state being attained after two successive transitions related to the magnetic structure of Ho.