NBIA Colloquium by David Nelson – Niels Bohr Institutet - Københavns Universitet

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NBIA Colloquium by David Nelson

(Harvard University and NBIA)

Defects on Cylinders:  Bacterial Cell Walls and Superfluid Helium Films

There is a deep analogy between the physics of crystalline solids and the behavior of superfluids, dating back to pioneering work of Philip Anderson, Paul Martin and others. The stiffness to shear deformations in a periodic crystal resembles the superfluid density that controls the behavior of supercurrents in neutral superfluids such as He4. Dislocations in solids have a close analogy with quantized vortices in superfluids.    Remarkable recent experiments on the way rod-shaped bacteria elongate their cell walls have focused attention on the dynamics and interactions of point-like dislocation defects in a cylindrical crystalline shell.   In this lecture, we review the physics of superfluid helium films on cylinders and discuss how confinement in one direction affects vortex interactions with supercurrents. Although there are similarities with the way dislocations respond to strains on cylinders, important differences emerge, due to the vector nature of the topological charges characterizing the dislocations.

Refreshments will be available in the NBIA lounge after the colloquium.