Ordered, disordered and coexistent stable vortex lattices in NbSe_2 single crystals

TL;DR

This study investigates vortex lattice configurations in NbSe2 single crystals near the peak effect using ac susceptibility, revealing stable, metastable, and coexistent vortex states with temperature-dependent order.

Contribution

It provides experimental evidence of stable, metastable, and coexistent vortex lattice states in NbSe2 near the peak effect, using ac susceptibility in the Campbell regime.

Findings

Stable vortex lattices are maximally ordered below T1(H).

Disordered configurations dominate above T2(H).

Intermediate disorder and coexistence occur between T1 and T2.

Abstract

It is commonly accepted that the peak effect (PE) in the critical current density of type II superconductors is a consequence of an order-disorder transition in the vortex lattice (VL). Examination of vortex lattice configurations (VLCs) in its vicinity requires the use of experimental techniques that exclude current induced VL reorganization. By means of linear ac susceptibility experiments in the Campbell regime, where vortices are forced to oscillate (harmonically) around their effective pinning potentials, we explore quasi-static stable and metastable VLCs in NbSe_{2} single crystals near the PE. We identify three different regions: for T<T_{1}(H), stable VLCs are maximally ordered. For T>T_{2}(H) configurations are fully disordered and no metastability is observed. In the T_{1}<T<T_{2} region we find temperature dependent stable configurations with intermediate degree of disorder, possibly associated to coexistence of ordered and disordered lattices throughout the PE. A simple estimation of the equilibrium proportion of ordered and disordered domains is provided.