Half-integer Shapiro steps at the 0-pi crossover of a ferromagnetic Josephson junction.
We investigate the current-phase relation of S/F/S junctions near the crossover between the 0 and the pi ground states. We use Nb/CuNi/Nb junctions where this crossover is driven both by thickness and temperature. For a certain thickness a nonzero minimum of critical current is observed at the crossover temperature. We analyze this residual supercurrent by applying a high frequency excitation and observe the formation of half-integer Shapiro steps. We attribute these fractional steps to a doubling of the Josephson frequency due to a sin((2phi) current-phase relation. This phase dependence is explained by the splitting of the energy levels in the ferromagnetic exchange field.
Sellier
Hermann
H
Département de Recherche Fondamentale sur la Matière Condensée, CEA-Grenoble, 17 rue des Martyrs, 38054 Grenoble, France.
Baraduc
Claire
C
Lefloch
François
F
Calemczuk
Roberto
R