Parallel magnetic field suppresses dissipation in superconducting nanostrips

TL;DR

Applying a parallel magnetic field to superconducting nanostrips can suppress vortex-induced dissipation, leading to a reentrant superconducting state, which challenges traditional views on magnetic field effects in superconductors.

Contribution

This study demonstrates that a parallel magnetic field can reduce vortex motion and dissipation in superconducting nanostrips, revealing a novel mechanism for enhancing superconductivity.

Findings

Resistance initially increases then drops with magnetic field

Reentrant superconducting state observed at high magnetic fields

Suppression of vortex unwinding instability due to magnetic field

Abstract

The motion of Abrikosov vortices in type-II superconductors results in a finite resistance in the presence of an applied electric current. Elimination or reduction of the resistance via immobilization of vortices is the "holy grail" of superconductivity research. Common wisdom dictates that an increase in the magnetic field escalates the loss of energy since the number of vortices increases. Here we show that this is no longer true if the magnetic field and the current are applied parallel to each other.Our experimental studies on the resistive behavior of a superconducting Mo$_{0.79}$Ge$_{0.21}$ nanostrip reveal the emergence of a dissipative state with increasing magnetic field, followed by a pronounced resistance drop, signifying a reentrance to the superconducting state. Large-scale simulations of the 3D time-dependent Ginzburg-Landau model indicate that the intermediate resistive state is due to an unwinding of twisted vortices. When the magnetic field increases, this instability is suppressed due to a better accommodation of the vortex lattice to the pinning configuration. Our findings show that magnetic field and geometrical confinement can suppress the dissipation induced by vortex motion and thus radically improve the performance of superconducting materials.