Peak effects induced by particle irradiations in 2H-NbSe2

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 (O-DO) 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 J(c) reveal the formation of non-uniform J(c) 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 O-DO 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.

Automated summary

Various peak effects induced by particle irradiations were investigated in 2H-NbSe2 single crystals. The peak effect induced by order-disorder transition of vortices was magnified by 3 MeV proton irradiation, while the peak effect in NbSe2 with splayed columnar defects showed a shift towards low fields with increasing splayed angle. Numerical calculations confirmed the mechanism behind the peak effect, and field dependence analysis revealed the formation of non-uniform J(c) flow. Coexistence of different peak effects was observed in symmetric splayed CD samples generated by Xe and Au ions, and a broad anomalous peak effect similar to iron-based superconductors was observed in Au-irradiated samples with small splay angle, which was suppressed by an externally applied magnetic field parallel to one of the splayed CDs.