Percolation Transition in the Heterogeneous Vortex State in NbSe2

TL;DR

This study identifies a universal percolation transition in the vortex state of NbSe2, where a critical volume fraction of disordered domains triggers a sharp increase in critical current, revealing fundamental vortex dynamics.

Contribution

It demonstrates the universality of the percolation threshold and critical exponent in the heterogeneous vortex phase of NbSe2, independent of temperature history and measurement speed.

Findings

Critical volume fraction Pc = 0.26 triggers transition.

Critical exponent r = 1.97 ± 0.66 is universal.

Transition depends on vortex heterogeneity and disorder.

Abstract

A percolation transition in the vortex state of a superconducting 2H-NbSe2 crystal is observed in the regime where vortices form a heterogeneous phase consisting of ordered and disordered domains. The transition is signaled by a sharp increase in critical current that occurs when the volume fraction of disordered domains, obtained from pulsed measurements of the current-voltage characteristics, reaches the value Pc= 0.26. Measurements on different vortex states show that while the temperature of the transition depends on history and measurement speed, the value of Pc and the critical exponent characterizing the approach to it, r =1.97 $\pm$ 0.66, are universal.