Why pinning by surface irregularities can explain the peak effect in transport properties and neutron diffraction results in NbSe2 and Bi-2212 crystals?

TL;DR

This paper presents a model explaining the peak effect in transport properties of NbSe2 and Bi-2212 superconductors through surface irregularities, aligning well with experimental data and neutron diffraction results.

Contribution

It introduces a quantitative model of vortex pinning by surface irregularities that accurately predicts critical currents and explains the peak effect in anisotropic superconductors.

Findings

Model accurately estimates critical current in different phases.

Surface irregularities can explain the peak effect phenomena.

Neutron diffraction data supports the coexistence of vortex states.

Abstract

The existence of a peak effect in transport properties (a maximum of the critical current as function of magnetic field) is a well-known but still intriguing feature of type II superconductors such as NbSe2 and Bi-2212. Using a model of pinning by surface irregularities in anisotropic superconductors, we have developed a calculation of the critical current which allows estimating quantitatively the critical current in both the high critical current phase and in the low critical current phase. The only adjustable parameter of this model is the angle of the vortices at the surface. The agreement between the measurements and the model is really very impressive. In this framework, the anomalous dynamical properties close to the peak effect is due to co-existence of two different vortex states with different critical currents. Recent neutron diffraction data in NbSe2 crystals in presence of transport current support this point of view.