Heidelberg 2015 – scientific programme
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A: Fachverband Atomphysik
A 18: Poster: Ultra-cold atoms, ions and BEC (with Q)
A 18.4: Poster
Tuesday, March 24, 2015, 17:00–19:00, C/Foyer
Degeneracy and inversion of band structure for Wigner crystals on a closed helix — •Alexandra Zampetaki1, Jan Stockhofe1, and Peter Schmelcher1,2 — 1Zentrum für Optische Quantentechnologien, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany — 2The Hamburg Centre for Ultrafast Imaging, Luruper Chaussee 149, 22761 Hamburg, Germany
Constraining long-range interacting particles to move on a curved manifold can drastically alter their effective interactions. As a prototype we explore the structure and vibrational dynamics of crystalline configurations formed on a closed helix. We show that the ground state undergoes a pitchfork bifurcation from a symmetric polygonic to a zig-zag-like configuration with increasing radius of the helix.
Remarkably, we find that for a specific value of the helix radius, below the bifurcation point, the vibrational frequency spectrum collapses to a single frequency. This allows for an essentially independent small-amplitude motion of the individual particles and consequently localized excitations can propagate in time without significant spreading. Increasing the radius beyond the degeneracy point, the band structure is inverted, with the out-of-phase oscillation mode becoming lower in frequency than the mode corresponding to the centre of mass motion.