Macroscopically Strain-Free Fe(Se,Te) Membrane

Thin films differ from bulk single crystals primarily in two aspects:
defect density and strain state. Due to the nature of the growth process,
superconducting thin films generally contain many more structural
defects than single crystals. These include threading dislocations, twin
or anti-phase boundaries, and precipitates. While such defects are
detrimental in some contexts, in superconducting films they often act
as strong pinning centers, significantly enhancing the critical current
density.
Another important difference is strain. Epitaxial films are typically
strained due to lattice mismatch with the substrate. This in-plane strain
can persist through a certain film thickness—and sometimes even
beyond—resulting in compensating strain along the out-of-plane
direction, often along the c-axis. This strain state can lead to
noticeable shifts in the critical temperature Tc, particularly in iron
based superconductors.
To decouple the effects of defect density and strain, and to facilitate a
more accurate comparison between thin films and bulk single crystals,
we have developed multiple techniques to obtain substrate-free
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Fe(Se,Te) thin films. These include adhesive cleavage at or slightly
above the film–substrate interface, as well as the use of a watersoluble
sacrificial buffer layer. In this presentation, I will examine the
structural and superconducting properties of the films prepared by
these two methods and discuss their correspondence to the behavior
observed in bulk single crystals.
References:
1) L. Masuda et al., submitted in Supercond. Sci. Technol.