Dr. Temo Vekua (Institute of Theoretical Physics, Leibniz University of Hannover)
"Spontaneous increase of magnetic flux and chiral-current reversal in bosonic ladders: Swimming against the tide"
The interplay between spontaneous symmetry breaking in many-body systems, the wave-like nature of quantum particles and lattice effects produces an extraordinary behavior of the chiral current of bosonic particles in the presence of a uniform magnetic flux defined on a two-leg ladder. While non-interacting as well as strongly interacting particles, stirred by the magnetic field and for values of the flux between a quarter and half-a-flux quantum, circulate in the ground state along the system's boundary in the counterclockwise direction, interactions can stabilize states with broken translational symmetry, in which the circulation direction can be reversed. For the Bose-Hubbard model on the two-leg ladder, the states with spontaneously broken translational symmetry are vortex lattices that we have observed numerically. We have also observed a ground state where density of bosons gets imballanced spontaneously between the ladder legs.