Monday, March 25, 2013

1303.5529 (E. B. Sonin)

Transverse force on a vortex in lattice models of superfluids    [PDF]

E. B. Sonin
The Letter addressees vortex dynamics for the lattice models of superfluids in the continuous approximation. The continuous approximation restores translational invariance absent in the original lattice model, but the theory is not Galilean invariant. As a result, calculation of the two transverse forces on the vortex, Magnus force and Lorentz force, requires the analysis of two balances, for the genuine momentum of particles in the lattice (Magnus force) and for the quasimomentum (Lorentz force) similar to that in the Bloch theory of particles in the periodic potential. While the developed theory yields the same Lorentz force, which was well known before, a new general expression for the Magnus force was obtained. The theory demonstrates how a small Magnus force emerges in the Josephson-junction array if the particle-hole symmetry is broken. The continuous approximation for the Bose--Hubbard model close to the superfluid-insulator transition was developed, which was used for calculation of the Magnus force. The theory shows that there is an area in the phase diagram for the Bose--Hubbard model, where the Magnus force has an inverse sign with respect to that which is expected from the sign of velocity circulation.
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