# CMT Seminar: Interacting Hofstadter spectrum of bosons in an artificial gauge field

Monday, January 31, 2011 – 3:15pm

Reiss 261A

Stephen Powell

University of Maryland

In the presence of a magnetic field, noninteracting particles on a lattice have a remarkable fractal spectrum, known as the “Hofstadter butterfly”. Motivated by experimental advances in the synthesis of gauge potentials for ultracold atoms, we consider the superfluid phase of interacting bosons on a square lattice in the presence of a magnetic field. We show that superfluid order implies spatial symmetry breaking, and predict clear signatures of many-body effects in time-of-flight measurements. We then develop a Bogoliubov expansion to describe the quasiparticle excitations, whose spectrum combines the intricacy the Hofstadter butterfly with the characteristic features of the superfluid phase.

References: S. Powell, R. Barnett, R. Sensarma, and S. Das Sarma, Phys. Rev. Lett. 104, 255303 (2010); Phys. Rev. A 83, 013612 (2011)

**Host:** Chris Varney