Peak-effect and surface crystal-glass transition for surface-pinned vortex array

TL;DR

This study investigates the peak effect in Nb crystals with surface pinning, revealing a transition from collective to individual pinning and a vortex crystal-glass transition caused by surface defects.

Contribution

It provides a combined experimental and theoretical analysis linking the peak effect to surface pinning transitions and vortex lattice softening.

Findings

Peak effect related to transition from collective to individual surface pinning.

Vortex crystal-glass transition induced by surface defects.

Softening of shear rigidity due to disorder-induced lattice deformations.

Abstract

The peak effect has been investigated in clean Nb crystals with artificially corrugated surfaces by measuring the linear surface impedance in the 1kHz-1MHz frequency range. From a two-mode analysis of the complex spectra, we establish that vortex dynamics is governed by surface pinning and deduce the associated vortex slippage length. We demonstrate experimentally and theoretically that the peak effect is related to a transition from collective to individual surface pinning. A proper account of the peak-effect anomalies implies softening of the shear rigidity by disorder-induced lattice deformations. This leads to a vortex crystal-glass transition induced by surface defects.