Supersolid He4 as a spontaneous Vortex Crystal
speaker: Ganapathy Baskaran (The Institute of Mathematical Sciences, Chennai 600 113, India)abstract: Superfluid He4 has a soft roton excitation branch. Roton is a quantized vortex loop of atomic dimension. Further, quantized vortices in superfluid He4 are energetically inexpensive, because the radius of the normal core of quantized vortices in He4 has only atomic dimension. It is shown that under pressure a superfluid to supersolid phase transition is induced by a macroscopic condensation of rotons. Condensing rotons fuse to form a dense hexagonal lattice of spontaneous quantized vortex antivortex filaments. In addition, there is a spontaneous staggered modulation of the vortex core radius along the filamens. There is also an interesting quantum effect, namely a small increase in the net atom density at the vortex core. The final result is an atom density wave of hcp symmetry and a complex ground state current pattern, suppored by the background superfluid. The number of atoms per unit cell is determined by parameters of the theory and is close to two. Remarkably, the rigidity of our supersolid (spontaneous vortex crystal) is determined by the underlying superfluid phase rigidity.
We provide two approaches, i) a weak coupling Bogoliubov theory and ii) a strong coupling Gross Pitaevski theory, where existence of soft roton branch is taken care of through a current-current coupling term. In addtion to supersolid phenomena, several of the puzzling anomalies such as existence of crystallization wave gets naturally explained in our theory. Our supersolid phase breaks parity and time reversal symmetry because of atom scale circulation in the ground state.
timetable:
Tue 17 Jul, 17:00 - 18:30, Aula Dini
Wed 18 Jul, 17:00 - 18:30, Aula Dini
documents:
Baskaran.ppt
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