Peak Effects Induced by Particle Irradiations in 2H-NbSe2

TL;DR

This study investigates peak effects in 2H-NbSe2 caused by particle irradiation, revealing how irradiation dose and defect splay angle influence vortex behavior and peak phenomena, supported by experimental and numerical analysis.

Contribution

It presents new experimental and numerical insights into how particle irradiation and defect splay angles induce and modify peak effects in 2H-NbSe2 superconductors.

Findings

Proton irradiation shifts peak effect from high to low fields with increased dose.

Splayed defect angles cause a transition from high to low field peak effects.

Coexistence of different peak effects observed in irradiated samples.

Abstract

Various peak effects in 2H-NbSe2 single crystals induced by particle irradiations were studied. 3 MeV proton irradiation magnified the peak effect induced by order-disorder transition of vortices, where the peak field shifts from high fields to low fields with increasing irradiation dose. For the peak effect in NbSe2 with splayed columnar defects (CDs), as the splayed angle increases, peak field gradually shifts from high fields to low fields. Numerical calculations have been conducted to investigate the mechanism of the peak effect. The calculated results exhibit excellent agreement with experimental observations. Analyses of field dependence of Jc reveal the formation of non-uniform Jc flow with increasing splayed angle, which plays a crucial role in inducing the self-field peak effect in superconductors with splayed CDs. In samples with symmetric splayed CDs with respect to the c-axis generated by 800 MeV Xe and 320 MeV Au ions, coexistence of order-disorder transition-induced peak effect and self-field peak effect was observed. In the case of 320 MeV Au irradiated samples, when the splay angle is small, the two peak effects transform into a broad peak, which has similarity to the anomalous peak effect observed in iron-based superconductors. Interestingly, the broad anomalous peak effect is strongly suppressed when the external magnetic field is applied parallel to one of splayed CDs.