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) standard 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)





Mechanically Controlled Multi-Contact Break Junctions

In this application, small tips made from either glass or graphite were used to locally deform a silicon membrane, creating break junctions in a very controlled fashion. The tips with a typical radius between 50 and 200 microns were precisely controlled using attocube’s nanopositioning technology. The approach of locally creating and controlling individual break junctions can be used to study the influence of optical excitations on the conductance of individual molecules and for controllable metallic single-electron transistors.


      Reprinted with permission from R. Waitz, O. Schecker and E. Scheer, Rev. Sci. Instrum. 79, 093901 (2008). © 2008, American Institute of Physics.





Automatic Mapping of Semiconductor Quantum Dots

Returning to interesting sample positions has never been easier: Yves Delley from the Quantum Photonics Group (QPG) at the ETH Zurich have – based on attocube positioners with resistive encoders – built a micro-photoluminescence (PL) setup and automated it to a great extent. They programmed a fully automated routine for raster-imaging a full sample of up to 4 x 4 mm² as well as implemented an auto-focus routine. Once initiated, the positioners are moved frame-by-frame and a CCD camera takes images of the PL of their semiconductor quantum dot samples. Knowing the coordinates of all individual images, it is easy to put together a complete map of the sample (see figure on the left).

“Now, we have to select the interesting dots, at which we want to take a closer look”, says Yves Delley, the responsible project researcher at QPG and gags: “Yet, in order to find the shortest route between all these quantum dots, we would need a quantum computer to solve this problem.”

      (Image kindly provided by Yves Delley, Quantum Photonics Group, ETH Zurich, Switzerland)





3D g-Factor Mapping of Single Quantum Dots

A xyz linear positioning stack combined with a rotator was used in a novel fiber-based confocal microscope, dedicated for the investigation of certain nanostructures such as InGaAs quantum dots (QDs) using magneto-photoluminescence (PL). The specific arrangement of positioners enabled scientists in this experiment to tilt and rotate samples at low temperature with respect to a magnetic field of up to 10 T while maintaining focus on a single QD.

      T. Kehoe, M. Ediger, R. T. Phillips, and M. Hopkinson, Rev. Sci. Instrum. 81 013906 (2010).





Scanning Microwave Impedance Microscopy at 4 K and 9 T

A set of linear positioners and scanners was implemented into a microwave impedance microscope located inside a liquid Helium flow cryostat equipped with a 9 T superconducting magnet [1]. The 1 GHz microwave signal was guided to the cantilever probe, which detected the dielectric constant and conductivity contrast of the sample during scanning. The system is a versatile tool for fundamental research on complex materials and phase transitions under various conditions.


      [1] K. Lai, M. Nakamura, W. Kundhikanjana, M. Kawasaki, Y. Tokura, M. A. Kelly, and Z.-X. Shen, Science 329, 190 (2010).





Magnetic Resonance Imaging of Nanoscale Tobacco Mosaic Virus at 300 mK

attocube’s ANPx51 positioners were used in an MRFM setup with the task to precisely and reliably position a magnetic tip and a copper nanowire to close proximity of an ultra-sensitive cantilever. The MRFM setup was applied to investigate and reconstruct the 1H spin distribution of Tobacco Mosaic Virus particles, representing a 100-million fold improvement in volume resolution over conventional MRI.


      C. L. Degen, M. Poggio, H. J. Mamin, C. T. Rettner, and D. Rugar,  PNAS 106, 1313 (2009).





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)





Dissipation in Optomechanical Resonators

The acoustic dissipation of microresonators was analyzed via a cryogenic interferometry setup. Hereby, a continuous flow 4He cryostat was utilized as sample chamber, which in turn was equipped with a stack of attocube’s ANPxyz51 positioners for the alignment of the sample with respect to an optical fiber. The fiber was part of a homodyne interferometer, allowing high signal-to-noise measurements of the eigenmodes of the resonator while keeping disturbances due to radiation pressure and optical fluctuations at a minimum. The turbo-pumped cryostat enabled interrogation from room temperature to 20 K, and from atmospheric pressure to vacuum levels of 2.5×10-7 millibar.


      G. D. Cole, et al., 23rd IEEE International Conference on Microelectromechanical Systems, Hong Kong SAR, China, 24–28 January 2010, TP133.





Lensless Imaging with X-Ray Waveguides

A synchrotron generated X-ray beam was coupled into an X-ray waveguide located in the focus of Kirkpatrick-Baez mirrors. The resulting filtered wave was then used to illuminate a sample coherently, yielding a magnified hologram of the sample recorded by a pixel detector. Several linear positioners, goniometers, and rotators were applied for precision alignment of the waveguide with respect to the sample, which in turn was mounted on a high-precision tomographic rotation stage.


      Reprinted with permission from S. Kalbfleisch et al., AIP. Conf. Proc., 1234, 433-436 (2010). © 2010, American Institute of Physics.





Special Micro X-ray Fluorescence Analysis (micro-XRF) Spectrometer

Confocal micro-XRF is a method to determine the spatial distribution of major, minor and trace elements within a sample in three dimensions. The employed polycapillary x-ray optics need to be aligned precisely to get optimal results. Very compact positioners had to be used inside the vacuum chamber for this purpose. Long time stability of the alignment is also a major requisite. ANPxyz101 nanopositioners fulfill these
requirements very well.
The figure to the left shows a 3D sample measurement of a cross made from 10 μm copper wire which is placed on an x-ray screen and fixed
using adhesive tape [1].


      [1] S. Smolek, C. Streli, N. Zoeger, and P. Wobrauschek, Rev. Sci. Instr. 81, 053707 (2010). (The data was kindly provided by S. Smolek and C. Streli, Atominstitut of the TU Wien.)





Development of a micromanipulator with an haptic interface

M. A. Srinivasan of MIT, USA and UCL, London, with support from TUM-IAS, Munich, has developed a micromanipulator with an haptic interface to enable manual exploration, manipulation, and assembly of micro-structures. In collaboration with A. Schmid of UCL, London, S. Thalhammer of Helmholtz Zentrum, Munich, and R. Yechangunja of Yantric, Inc., USA, he has demonstrated manual grasping and moving of 10 to 100 µm sized objects with direct haptic feedback of the gripping force in real-time, so that the objects can be placed in three dimensions with nanometer precision [1].
A force-sensing microgripper with 100 µm opening is mounted on an ANPxyz101/NUM stack of attocube’s closed loop positioners. Measured forces by the microgripper in the micro-Newton range are scaled up and exerted on the operator’s fingers through a haptic interface.


      [1] A. Schmid, R. Yechangunja, S. Thalhammer, and M. A. Srinivasan, Proceedings of the
IEEE Haptics Symp., 517-522 (2012). (Images are courtesy of A. Schmid, S. Thalhammer,
and M. A. Srinivasan)





Controlling Electron Emission in Space and Time

The dynamics of electrons emitted from a sharp tungsten tip triggered by femtosecond laser pulses have been investigated. The setup shown to the left is situated in an UHV chamber at p = 10-10 mbar pressure. A xyz positioning stack enables precision alignment of the tip. Photoelectron spectra are recorded while the phase between carrier wave and intensity envelope is varied in small steps. The lower figure shows two electron spectra, recorded with a phase difference of 180 degrees. In a), pronounced peaks are visible caused by interference of two electron wave packets emitted during subsequent optical cycles. In b), no peak structure is visible; only one electron wave packet contributes. This energy domain effect allows conclusions about the time dynamics of the electrons. By shaping the laser electric field with the carrier-envelope phase, the dynamics of the electrons can be controlled with attosecond precision. The presented system enables control over photoelectrons from a metal tip in space (nanometer scale) and time (attosecond scale).


      (The data was kindly provided by M. Krüger, M. Schenk, and P. Hommelhoff, Max Planck Institute of Quantum Optics, Garching, Germany.)

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