Force-free state in a superconducting single crystal and angle-dependent vortex helical instability

Abstract

Superconducting 2H-NbSe_2 single crystals show intrinsic low pinning values. Therefore, they are ideal materials with which to explore fundamental properties of vortices. (V, I) characteristics are the experimental data we have used to investigate the dissipation mechanisms in a rectangular-shaped 2H-NbSe_2 single crystal. Particularly, we have studied dissipation behavior with magnetic fields applied in the plane of the crystal and parallel to the injected currents, i.e., in the force-free state where the vortex helical instability governs the vortex dynamics. In this regime, the data follow the elliptic critical state model and the voltage dissipation shows an exponential dependence, V α e^{[( α ( I-I_(c _II))]}, I_(cII)being the critical current in the force-free configuration and a a linear temperature-dependent parameter. Moreover, this exponential dependence can be observed for in-plane applied magnetic fields up to 40 ° off the current direction, which implies that the vortex helical instability plays a role in dissipation even out of the force-free configuration.