Abstract
We investigate the current-phase relation of junctions near the crossover between the 0 and the ground states. We use 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 current-phase relation. This phase dependence is explained by the splitting of the energy levels in the ferromagnetic exchange field.
- Received 10 February 2004
DOI:https://doi.org/10.1103/PhysRevLett.92.257005
©2004 American Physical Society