Selected Applications
Premium Line - transport measurements
Slow & Fast Vortices in Iron Pnictide Superconductors
Using the attocube ANR31 rotator, a precise nano-rotator setup was designed
to fit on a small (25 mm diameter) standard sample carrier. We have investi-
gated the vortex matter of the iron-pnictide high temperature superconduc-
tors [1]. We studied the mobility of magnetic vortices in the layered super-
conductor SmFeAs(O,F) and could show an enormous enhancement of vortex
mobility associated with a transition of the vortex nature itself, changing
from Abrikosov to Josephson-type. A perfectly in-plane Josephson vortex,
centered in a “non-superconducting” Sm(O,F) layer, can only be weakly pinned
and thus experiences the mentioned enhancement in mobility.
This feature, however, is immediately lost if the field is tilted out of the FeAs
planes and even the smallest misalignment (< 0.1°) completely destroys the
effect as the misaligned vortex is not parallel to the crystallographic layers
anymore. As mobile vortices cause dissipation, their mobility is observed as a
very sharp spike in voltage as shown in Fig. 1 (see also [1]). Therefore angular
precision and stability is the key to observing this effect. The discovered
Abrikosov to Josephson transition was unexpected, as the materials’ elec-
tronic anisotropy is low. Moreover, Josephson vortices are b