  Superconducting (Li1-xFex)OHFe1-ySe films are attractive for both the basic
research and practical application. However, the conventional vapor deposition
techniques are not applicable in synthesizing the films of such a complex
system. So no intrinsic charge transport measurements on the films are
available so far to reveal the nature of charge carriers, which is fundamental
to understanding the iron-based superconductivity mechanism. Herein we report a
soft chemical film technique (matrix-assisted hydrothermal epitaxial growth),
by which we have succeeded in growing a series of (Li1-xFex)OHFe1-ySe films
covering the whole superconducting regime, with the superconducting transition
temperature (Tc) from 4 K up to 42 K. This film technique opens up a new way
for fabricating other complex functional materials as well. Furthermore, our
systematic transport investigation on the film samples indicates that both the
electron and hole carriers contribute to the charge transport, with the
scattering rates deviating from the Fermi liquid. We find that the
superconductivity occurs upon the electron and hole mobility becoming
divergent. And in the high Tc samples, the electron carriers are found much
more mobile than the holes, a feature distinct from the low Tc samples. Hence,
our transport results provide key insights into the underlying physics for
iron-based high-Tc superconductivity.
