Intrinsic pinning and the critical current scaling of clean epitaxial Fe(Se,Te) thin films

Abstract

We report on the transport properties of clean, epitaxial Fe(Se,Te) thin films prepared on Fe-buffered MgO (001) single crystalline substrates by pulsed laser deposition. Near ${T}_{\mathrm{c}}$ a steep slope of the upper critical field for $H||ab$ was observed (74.1 T/K), leading to a very short out-of-plane coherence length, ${\ensuremath{\xi}}_{\mathrm{c}}(0)$, of 0.2 nm, yielding 2${\ensuremath{\xi}}_{\mathrm{c}}(0)\ensuremath{\approx}0.4\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$. This value is shorter than the interlayer distance (0.605 nm) between the Fe-Se(Te) planes, indicative of modulation of the superconducting order parameter along the $c$ axis. An inverse correlation between the power law exponent $N$ of the electric field-current density($E$-$J$) curve and the critical current density ${J}_{\mathrm{c}}$ has been observed at 4 K, when the orientation of $H$ was close to the $ab$ plane. These results prove the presence of intrinsic pinning in Fe(Se,Te). A successful scaling of the angular dependent ${J}_{\mathrm{c}}$ and the corresponding exponent $N$ can be realized by the anisotropic Ginzburg Landau approach with appropriate $\ensuremath{\Gamma}$ values $2\ensuremath{\sim}3.5$. The temperature dependence of $\ensuremath{\Gamma}$ behaves almost identically to that of the penetration depth anisotropy.