Spectroscopy of the Fractional Vortex Eigenfrequency in a Long Josephson 0-κ Junction

Fractional Josephson vortices carry a magnetic flux Φ, which is a fraction of the magnetic flux quantum Φ₀≈2.07×10^-15Wb. Their properties are very different from the properties of the usual integer fluxons. In particular, fractional vortices in 0-κ Josephson junctions are pinned and have an oscillation eigenfrequency which is expected to be within the Josephson plasma gap. Using microwave spectroscopy, we investigate the dependence of the eigenfrequency of a fractional Josephson vortex on its magnetic flux Φ and on the bias current. The experimental results are in good agreement with the theory.