Structural, electro-magnetic, and optical properties of Ba(Fe,Ni)₂As₂ single-crystal thin film

We investigated the superconducting transition temperature (T _c), critical current density (J _c) and optical properties of optimally doped Ba(Fe_0.95Ni_0.05)₂As₂ (Ni-Ba122) single-crystalline epitaxial thin films grown by pulsed laser deposition for the first time. The T _c at zero resistivity was about 20.5 K and the J _c at self-field and 4.2 K was 2.8 MA cm^-2 calculated by the Bean model. The superconducting properties such as T _c and J _c of thin films are comparable to those of bulk single-crystal samples. The superfluid plasma frequency (λ _p,S) of Ni-Ba122 thin film is ∼7033 cm^-1 obtained by optical spectroscopic technique. Based on this plasma frequency, we obtained the London penetration depth (λ _L), ∼226 nm at 8 K, which is comparable to those of optimally Co- and K-doped BaFe₂As₂ single crystals.