Effective action approach to the p-band Mott insulator and superfluid transition
Xiaopeng Li,1, 2
and W. Vincent Liu1, 2,
Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
Kavli Institute for Theoretical Physics, University of California, Santa Barbara, CA 93106, USA
Department of Physics and Astronomy, George Mason University, Fairfax, Virginia 22030, USA
Motivated by the recent experiment on p-orbital band bosons in optical lattices, we study the-
oretically the quantum phases of Mott insulator and superfluidity in two-dimensions. The system
features a novel superfluid phase with transversely staggered orbital current at weak interaction,
and a Mott insulator phase with antiferro-orbital order at strong coupling and commensurate filling.
We go beyond mean field theory and derive from a microscopic model an effective action that is
capable of describing both the p-band Mott insulating and superfluid phases in strong coupling. We
further calculate the excitation spectra near the quantum critical point and find two gapless modes
away from the tip of the Mott lobe but four gapless modes at the tip. Our effective theory reveals
how the phase coherence peak builds up in the Mott regime when approaching the critical point.