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Vortices in transition

Rotating a bucket of superfluid and putting a superconductor in external magnetic fields have one thing in common: the flux can only penetrate the system in the form of vortex lines. For an ideal system without any impurity, these vortex lines form a triangular vortex lattice, called the Abrikosov lattice. In the presence of impurities that are always there in any real materials, the vortex lines are subject to an additional “pinning’’ force that tends to pin the vortices to the impurities. Study of vortex pinning is of great importance in many practical applications of high Tc superconductors.

Cooling and confining a cloud of atoms can force them to form a type of matter known as a Bose-Einstein condensate. A condensate under rotation also supports a triangular vortex lattice. These gaseous atomic systems, unlike solids or liquids, are intrinsically clean. It is, however, possible to design the “impurities” for them. For example, by putting a rotating condensate in laser light field with spatially varying intensity patterns, the vortices will be pushed and pulled by the grid of laser beams and get pinned at the antinodes of the light field. Tuning the lasers will force the vortices to go through a series of different arrangements. Therefore, exploring the structural patterns of condensate vortex lattice allows us to study the vortex pinning problem in a controlled way, as proposed by the research group of Han Pu at Rice, with collaborators Nick Bigelow at Univ. of Rochester and Leslie Baksmaty at Georgia Tech.

 

Pu Feb 06
Vortices (little black holes) are pinned onto the antinodes of a laser field with square intensity patterns.