Enhancement of the vortex critical velocity in superconducting/normal metal bilayers

This study investigates the influence of normal metal thickness on the Larkin-Ovchinnikov (LO) instability in superconductor/normal metal heterostructures. Bilayers were fabricated using a 22 nm-thick Mo2N layer, with varying Pt, W, and Al thicknesses. The samples exhibited a critical temperature of approximately 7.5 K. The LO instability was characterized through current-voltage curves, which relate the maximum vortex velocity to the recombination time of normal electrons into Cooper pairs (tau). The results reveal a significant enhancement in vortex velocity at moderate and high magnetic fields when a metallic layer with thickness exceeding the coherence length is added. Furthermore, a direct correlation is observed between velocity values and the thermal conductance of the metal, indicating a contribution from phonons and heat dissipation to the maximum achievable velocity in the heterostructures.