Evolution of superconductivity dependence on substrate temperature with thickness of Fe(Se,Te) coated conductors deposited on metal tapes

Abstract

Fe(Se,Te) films of different thicknesses were deposited on metal tapes by pulsed laser deposition at different substrate temperatures. It is found that the substrate temperature dependence of superconductivity changes with the Fe(Se,Te) film thickness. When fabricating thin Fe(Se,Te) films with a thickness of about 150 nm, moderate substrate temperatures are conducive to balancing the influence of texture and stoichiometry on superconductivity, contributing to the obtainment of good superconductivity. When the Fe(Se,Te) films’ thickness is about 300 nm, the optimal substrate temperatures are lowered due to the determination of film superconductivity by the inhomogeneity of longitudinal chalcogen distribution via the cooperation of Te loss in the long-term-ablated target and the attraction of metal ions in the buffer layer. In addition, with a further increase in thickness from 300 to 600 nm, the self-field critical current of thick Fe(Se,Te) films continuously increases, but the critical current density increases first and then decreases, which is thought to be a result of the misoriented grains or non-superconducting phase due to the large deviation between the actual deposition temperature and the set substrate temperature, and the Se excess in the film. In addition, the 450-nm-thick Fe(Se,Te) film exhibits excellent self-field and in-field performances at 4.2 K: 1.308 MA/cm2 at self-field and over 0.5 MA/cm2 at 9 T. Point pinning, which is the local lattice disturbance randomly distributed in the film observed by transmission electron microscopy, dominates over the entire temperature range.

Unveiling the growth mechanism of FeSeTe films by pulsed laser deposition technique

“…These isolated islands result in the poor grain connectivity and rough surface of FeSeTe film [34]. With increasing T s , the isolated islands become larger due to the enhanced diffusion rate and nucleation rate [35,36], which can be evidenced by the gradually decreasing voids density and the reduced R rms . In addition, the thickness of the FeSeTe films increases with increasing T s within the T s range of 25 • C-400 • C (figure 2(p)), indicating the enhanced diffusion rate and nucleation rate with T s , which is consistent with the results of surface morphologies observed in the AFM images.…”

Performance improvement of iron chalcogenide films grown at high laser repetition rates by pulsed laser deposition

“…This is caused by the lack of iron in FST films, resulting in a relatively high amount of the semiconductor elements Se and Te. 37,46 A criterion of 10% and 90% of the normal state resistance at 20 K is used to define 𝑇 zero c and 𝑇 onset c , respectively. The difference between 𝑇 zero c and 𝑇 onset c is defined as the transition width Δ𝑇 c .…”

“…It is observed that the resistance of all FST films decreases with increasing temperature in the normal state, exhibiting a semiconducting behavior. This is caused by the lack of iron in FST films, resulting in a relatively high amount of the semiconductor elements Se and Te 37,46 . A criterion of 10% and 90% of the normal state resistance at 20 K is used to define $$T_{\mathrm{c}}^{{\mathrm{zero}}}$$ and $$T_{\mathrm{c}}^{{\mathrm{onset}}}$$, respectively.…”

“…The laser energy density was 2 J/cm 2 . The FST films with the thickness of 300 ± 20 nm were grown using a process of high substrate temperature of 430 • C followed by low substrate temperature of 330 • C. 37 During the deposition process, the tape moved back and forth across the coating area at a speed of 6 m/h. When the deposition process finished, the samples were moved away from the heating zone and naturally cooled to room temperature while maintaining vacuum.…”

“…The laser energy density was 2 J/cm 2 . The FST films with the thickness of 300 ± 20 nm were grown using a process of high substrate temperature of 430°C followed by low substrate temperature of 330°C 37 . During the deposition process, the tape moved back and forth across the coating area at a speed of 6 m/h.…”