Vortex Chains and Vortex Jets in MoSi Microbridges

Superconducting bridges exhibit many properties of a Josephson junction, such
as the electromagnetic radiation at overcritical currents I > I_c and steps in the
microwave-irradiated current–voltage (I–V ) curves. These Josephson effects stem from the periodic motion of magnetic flux quanta (vortices) in the narrowest region of the bridge. According to the Aslamazov and Larkin (AL) theory, the I–V curve of such a constriction should exhibit voltage kinks each time the number of vortices in the 1D vortex chain is increased by one. However, in the presence of defects and fluctuations, the intervortex repulsion stipulates the formation of a 2D vortex jet, which goes beyond the 1D AL model. Here, by milling one or two slits across a MoSi thin strip, we make vortices to move in a vortex–jet or a vortex–chain fashion, respectively. Unexpectedly, for the strip with a vortex jet, we observe equidistant voltage kinks at transport currents I ≃ 2Ic which are rather far from the assumption of I ~ Ic in the AL model. At the moment, we have no explanation for this observation, tending to attribute it to fast relaxation processes in MoSi and looking forward for a comparison with other superconducting materials.