  In layered superconductors the order parameter may be modulated within the
unit cell, leading to non-trivial modifications of the vortex core if the
interlayer coherence length $\xi_c(T)$ is comparable to the interlayer
distance. In the iron-pnictide SmFeAs(O,F) ($T_c \approx 50$K) this occurs
below a cross-over temperature $T^\star \approx 41$K, which separates two
regimes of vortices: anisotropic Abrikosov-like at high and Josephson-like at
low temperatures. Yet in the transition region around $T^\star$, hybrid
vortices between these two characteristics appear. Only in this region around
$T^\star$ and for magnetic fields well aligned with the FeAs layers, we observe
oscillations of the c-axis critical current $j_c(H)$ periodic in
$\frac{1}{\sqrt{H}}$ due to a delicate balance of intervortex forces and
interaction with the layered potential. $j_c(H)$ shows pronounced maxima when a
hexagonal vortex lattice is commensurate with the crystal structure. The narrow
temperature window in which oscillations are observed suggests a significant
suppression of the order parameter between the superconducting layers in
SmFeAs(O,F), despite its low coherence length anisotropy ($\gamma_\xi \approx
3-5$).
