Effective action approach to the p-band Mott insulator and superfluid transition

TL;DR

This paper develops an effective action framework to analyze quantum phase transitions between Mott insulator and superfluid phases in p-band bosons in 2D optical lattices, revealing novel phases and critical behaviors.

Contribution

It introduces a microscopic-derived effective action that captures both Mott insulator and superfluid phases, including novel orbital order and excitation spectra near criticality.

Findings

Discovery of a superfluid phase with transverse orbital current

Identification of four gapless modes at the Mott lobe tip

Analysis of phase coherence buildup near the quantum critical point

Abstract

Motivated by the recent experiment on p-orbital band bosons in optical lattices, we study theoretically 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. We also discuss the finite temperature phase transition of p-band superfluidity.