Nanogallery
Nanogallery
TODAY DECEMBER 12, 2018

Magnetic enhancement of superconductivity

Critical current increase in response to the applied magnetic field
Magnetic fields have long been known to suppress superconductivity through two main effects: first, by aligning the electron spins (Zeeman effect) and second, by raising the kinetic energy of condensed electrons via Meissner screening currents. Remarkably, in contrast with these expectations that have stood for some fifty years, it was recently discovered that magnetic fields can enhance the critical supercurrent in Nb and MoGe wires with very small diameters (typically less than 10 nm). The anomalous enhancement reaches the maximum at the field of 2-4 Tesla and is followed by usual decrease at higher fields.

The graph shows curves representing how the critical supercurrent of nanowires changes with applied magnetic field. The increase of the critical current is clearly seen. It is followed by the usual decline at higher fields.

To explain this phenomenon it is conjectured that magnetic moments are spontaneously generated on the surface of nanowires. Their destructive effect (with regard to superconductivity), active at lower magnetic fields, is suppressed by higher fields. Microscopic theory which quantitatively explains all experimental observations is shown as black dashed curves. The experimental group is lead by Prof. Alexey Bezryadin at Physics/UIUC. The theory group is lead by Prof. Paul Goldbart at Physics/UIUC.
See also images:
Magnetic field tends to line up the moments. Thus their destructive effect on the superconducting characteristics of the nanowire is reduced.
Magnetic field tends to line up the moments. Thus their destructive effect on the superconducting characteristics of the nanowire is reduced.

Related Links:
  • Full text of the paper ("Magnetic-Field Enhancement of Superconductivity in Ultranarrow Wires" Phys.Rev.Lett V.97 p.137001 (2006))
  • This electron microscope image clearly shows the tightly packed cylinders of gold nanoparticles.
The image is courtesy Eugene Zubarev/Rice University
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    Biomolecules
    http://perso.curie.fr/Simon.Sc..


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