Molecular Beam Epitaxy Growth of Superconducting Sr1-xKxFe₂As₂and Ba1-xKxFe₂As₂

We report on the molecular beam epitaxy growth of nonsuperconducting SrFe 2 As 2 and BaFe 2 As 2 and superconducting Sr 1- x K x Fe 2 As 2 and Ba 1- x K x Fe 2 As 2 thin films. SrFe 2 As 2 and BaFe 2 As 2 films were obtained rather easily at the growth temperatures of 540–600 °C, which are not much different from those for GaAs growth. However, superconducting Sr 1- x K x Fe 2 As 2 and Ba 1- x K x Fe 2 As 2 films cannot be obtained at the same growth temperatures as elemental K is highly volatile. The key to incorporating K into films is low-temperature growth (≤350 °C) in reduced As flux. The resultant films showed good superconducting properties: T c on ( T c end ) = 33.2 K (30.0 K) and 38.3 K (35.5 K) for Sr 1- x K x Fe 2 As 2 and Ba 1- x K x Fe 2 As 2 thin films respectively.