attoMOTION
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Selected Applications
attoMOTION
mK STM Image with Atomic Resolution
STM image of an aluminum (100) surface with atomic resolution. The image size is
about 29 x 20 nm². The corrugation is between 300fm and 800fm, depending on the
direction of the line profile. Defects show up as ring-like structures with different radii
depending of their depth. The image was measured in a homebuilt mK-STM at the
Max-Planck Institute for Solid State Research in Stuttgart, which uses an attocube
ANPz51 positioner for coarse approach.
(Image courtesy of Department of K. Kern, Max-Planck Institute for Solid State Research, Stuttgart, Germany)
Al(100)
T=15mK
U=10mV
I=1nA
Transition from Slow Abrikosov to Fast Moving Josephson 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) st andard sample carrier. We have investigated the vortex matter
of the iron-pnictide high temperature superconductors [1]. We studied the mobility of
magnetic vortices in the layered superconductor 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’
electronic anisotropy is low. Moreover, Josephson vortices are believed to be a feature of
highly anisotropic superconductors. This finding challenges our “global” understanding
of superconducting anisotropies and their relevance for the microscopic, intra-unit cell
modulation of the order parameter.
[1] P.J.W. Moll, L. Balicas, V. Geshkenbein, G. Blatter, J. Karpinski, N.D. Zhigadlo, and B. Batlogg, Nature Materials 12, 134 (2013)
(Data and Images courtesy of Philip Moll,et al. Laboratory of Solid State Physics, ETH Zurich, Switzerland)