Observation of anion-stoichiometry phase separation in Fe(Te,Se) film

Nanostructure control is of fundamental and technological importance because various properties such as vortex pinning in superconductors are determined by the nanostructure. While the nanostructure in superconducting oxides is well controlled, the nanostructure control of iron-based superconductors is required. The nanostructure has not yet been well controlled even in Fe(Te,Se) with the simplest structure among Fe-based superconductors because the anion may be non-stoichiometric and anionic substitution is possible. In this study, we observed the compositional inhomogeneity originating from phase separation in Fe(Te,Se) films, which were prepared by pulsed laser deposition. The films deposited at lower temperature do not show nanoscale compositional inhomogeneity. On the other hand, the high-temperature deposited films contain an inhomogeneous anion distribution with the size of similar to 8 nm due to phase separation. The spacing of the compositional inhomogeneity is similar to 16 nm. This structure obtained by phase separation is expected to be an effective pinning center in high magnetic fields after further optimization. Thus, the method of nanostructure control other than nanocomposite formation in oxides is demonstrated for Fe(Te,Se). Published under an exclusive license by AIP Publishing.

Automated summary

The control of nanostructure is crucial in both fundamental and technological aspects, as it determines various properties of superconductors such as vortex pinning. Although the nanostructure control in superconducting oxides is well-established, it remains challenging in iron-based superconductors due to the possibility of anionic substitution and non-stoichiometric anion. In this study, compositional inhomogeneity originating from phase separation was observed in Fe(Te,Se) films prepared through pulsed laser deposition. The compositional inhomogeneity was absent in films deposited at lower temperature, while high-temperature deposited films showed an anion distribution with the size of about 8 nm due to phase separation. The obtained structure is expected to function as an effective pinning center in high magnetic fields after further optimization, demonstrating a novel method of nanostructure control in Fe(Te,Se) different from nanocomposite formation in oxides.