Enhancement of $J$$_c$ by Proton Irradiation in HgBa$_2$Ca$_2$Cu$_3$O$_8$$_+$$_\delta$ Single Crystals

TL;DR

Proton irradiation significantly enhances the critical current density in HgBa$_2$Ca$_2$Cu$_3$O$_8$$_+eta$ single crystals by introducing effective pinning centers, with notable improvements at low temperatures and specific doses.

Contribution

This study demonstrates the effectiveness of proton irradiation in increasing the critical current density of Hg-based cuprate superconductors by modifying their vortex pinning properties.

Findings

Critical current density increased from 5.5 MA/cm$^2$ to 26 MA/cm$^2$ at 2 K after irradiation.

Critical current density remains above 0.1 MA/cm$^2$ at 77 K for irradiated samples.

A change in the pinning mechanism was observed post-irradiation.

Abstract

Critical current density is the key parameter for the practical application of superconductivity. In this study, 3 MeV proton irradiation experiments were conducted on HgBa$_2$Ca$_2$Cu$_3$O$_8$$_+$$_\delta$ single crystals to introduce pinning centers. The critical current density is found to be strongly enhanced after the irradiation with its maximum at a dose of 1$\times$10$^{16}$/cm$^2$, where the self-field critical current density at 2 K is enhanced from 5.5 MA/cm$^2$ to 26 MA/cm$^2$. At 77 K, the self-field critical current density for all irradiated crystals is over 0.1 MA/cm$^2$. The power-law dependence of the critical current density on the magnetic field is observed after irradiation, with a large power-law exponent $\alpha$ close to 1. A monotonic magnetic field dependence of the normalized magnetic relaxation rate is observed, which could be attributed to the low irreversibility field caused by the large anisotropy in Hg1223 single crystals. Through the analysis of the pinning force density of the crystal before and after irradiation, a clear mechanism change has been observed.