Vortex Chains and Vortex Jets in MoSi Microbridges

Abstract

Superconducting bridges exhibit many properties of a Josephson junction, such as the electromagnetic radiation at overcritical currents 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 which are rather far from the assumption of 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.

Fast dynamics of vortices in superconductors

“…An approach for the quantitative determination of n v and v * has recently been demonstrated experimentally [213][214][215]. The idea is based on the Aslamazov and Larkin (AL) prediction [216] of kinks in the I-V curves of wide and short superconducting constrictions when the number of vortices crossing the constriction is increased by one.…”

“…The idea is based on the Aslamazov and Larkin (AL) prediction [216] of kinks in the I-V curves of wide and short superconducting constrictions when the number of vortices crossing the constriction is increased by one. Such conditions were realized for a-few-micrometer-wide MoSi [213,214] and MoN [215] thin strips in which slits, milled by a focused ion beam [217], locally suppress the edge barrier and allow for a controllable vortex entry. The edge-barrier asymmetry gives rise to negative differential resistance [218] and superconducting diode effects [219], opening up prospects for studies of vortex guiding [100,111,112] and ratchet [17,220,221] effects in the few-and single-fluxon regimes.…”