Effects of heavy-ion irradiation on FeSe

Abstract

We report the effects of heavy-ion irradiation on FeSe single crystals by irradiating Uranium up to a dose equivalent matching field of $B_{\varphi }$ = 16 T. Almost continuous columnar defects along the $c$-axis with a diameter $\sim$10 nm are confirmed by high-resolution transmission electron microscopy. $T_c$ is found to be suppressed by introducing columnar defects at a rate of d$T_c$/d$B_{\varphi }$ $\sim$ -0.29KT${}^{-1}$, which is much larger than those observed in iron pnictides. This unexpected large suppression of $T_c$ in FeSe is discussed in relation to the large diameter of the columnar defects as well as its unique band structure with a remarkably small Fermi energy. The critical current density is first dramatically enhanced with irradiation reaching a value over $\sim$2$\times$10${}^5$ A/cm${}^2$ ($\sim$5 times larger than that of the pristine sample) at 2 K (self-field) with $B_{\varphi }$ = 2 T, then gradually suppressed with increasing $B_{\varphi }$. The $\delta$$l$-pinning associated with charge-carrier mean free path fluctuations, and the $\delta$$T_c$-pinning associated with spatial fluctuations of the transition temperature are found to coexist in the pristine FeSe, while the irradiation increases the contribution from $\delta$$l$-pinning, and makes it dominant over $B_{\varphi }$ = 4 T.

8 pages, 6 figures

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• Increase of critical current density in FeSe superconductor by strain effect
• Enhancement of $J$${}_c$ by Proton Irradiation in HgBa${}_2$Ca${}_2$Cu${}_3$O${}_8$${}_{+}$${}_{\delta }$ Single Crystals