  The intercalated iron selenide (Li,Fe)OHFeSe has a strongly layered structure
analogous to the quasi two-dimensional (2D) bismuth cuprate superconductors,
and exhibits both high-temperature (Tc) and topological superconductivity.
However, the issue of its superconductivity dimensionality has not yet been
fully investigated so far. Here we report that the quasi-2D superconductivity
features, including the high anisotropy {\gamma} = 151 and the associated
quasi-2D vortices, are also revealed for (Li,Fe)OHFeSe, based on systematic
experiments of the electrical transport and magnetization and model fittings.
Thus, we establish a new vortex phase diagram for (Li,Fe)OHFeSe, which
delineates an emergent quasi-2D vortex-liquid state, and a subsequent
vortex-solid dimensional crossover from a pancake-like to a three-dimensional
state with decreasing temperature and magnetic field. Furthermore, we find that
all the quasi-2D characteristics revealed here for the high-Tc iron selenide
superconductor are very similar to those reported for the high-Tc bismuth
cuprate superconductors.

Superconductivity