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Register a new userSystematic study on transport properties of FeSe thin films with various degrees of strain
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We performed systematic studies on the transport properties of FeSe thin films with controlled degrees of in-plane lattice strain, including both tensile and compressive strains. The superconducting transition temperature, $T_{mathrm c}$, increases up to 12 K for films with compressive strain while the superconductivity disappears for films with large tensile strains. On the other hand, the structural (nematic) transition temperature, $T_{mathrm s}$, slightly decreases as the in-plane strain is more compressive. This suggests that the structural transition can be extinguished by a smaller amount of Te substitution for films with more compressive strain, which may lead to higher $T_{mathrm c}$ in FeSe$_{1-x}$Te$_x$. It was also found that the carrier densities evaluated via transport properties increase as the in-plane strain becomes more compressive. A clear correlation between $T_{mathrm c}$ and the carrier densities suggests that it is essential to increase carrier densities for the $T_{mathrm c}$ enhancement of iron chalcogenides.
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FeSe0.5Te0.5 thin films were grown by pulsed laser deposition on CaF2, LaAlO3 and MgO substrates and structurally and electro-magnetically characterized in order to study the influence of the substrate on their transport properties. The in-plane lattice mismatch between FeSe0.5Te0.5 bulk and the substrates shows no influence on the lattice parameters of the films, whereas the type of substrates affects the crystalline quality of the films and, therefore, the superconducting properties. The film on MgO showed an extra peak in the angular dependence of critical current density Jc({theta}) at {theta} = 180{deg} (H || c), which arises from c-axis defects as confirmed by transmission electron microscopy. In contrast, no Jc({theta}) peaks for H || c were observed in films on CaF2 and LaAlO3. Jc({theta}) can be scaled successfully for both films without c-axis correlated defects by the anisotropic Ginzburg-Landau (AGL) approach with appropriate anisotropy ratio {gamma}J. The scaling parameter {gamma}J is decreasing with decreasing temperature, which is different from what we observed in FeSe0.5Te0.5 films on Fe-buffered MgO substrates.
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