Document Type

Article

Publication Date

Fall 9-5-2003

Publication Title

Physical Review Letters

ISSN

0031-9007

Volume

91

Issue

10

First Page

100402-1

Last Page

100402-4

DOI

10.1103/PhysRevLett.91.100402

Abstract

We directly image Tkachenko waves in a vortex lattice in a dilute-gas Bose-Einstein condensate. The low (sub-Hz) resonant frequencies are a consequence of the small but nonvanishing elastic shear modulus of the vortex-filled superfluid. The frequencies are measured for rotation rates as high as 98% of the centrifugal limit for the harmonically confined gas. Agreement with a hydrodynamic theory worsens with increasing rotation rate, perhaps due to the increasing fraction of the volume displaced by the vortex cores. We also observe two low-lying m=0 longitudinal modes at about 20 times higher frequency.

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