Bose Hubbard Model in a Strong Effective Magnetic Field: Emergence of a Chiral Mott Insulator Ground State

TL;DR

This paper investigates the phase diagram of the frustrated Bose-Hubbard model under strong magnetic fields, revealing a novel chiral Mott insulator state with broken time-reversal symmetry, using numerical simulations.

Contribution

It introduces the existence of a chiral Mott insulator in the frustrated Bose-Hubbard model at intermediate correlations, supported by DMRG and Monte Carlo methods.

Findings

Identification of a chiral Mott insulator with a gap to all excitations

Observation of staggered loop currents breaking time-reversal symmetry

Characterization of the CMI as a vortex supersolid or exciton condensate

Abstract

Motivated by experiments on Josephson junction arrays, and cold atoms in an optical lattice in a synthetic magnetic field, we study the "fully frustrated" Bose-Hubbard (FFBH) model with half a magnetic flux quantum per plaquette. We obtain the phase diagram of this model on a two-leg ladder at integer filling via the density matrix renormalization group approach, complemented by Monte Carlo simulations on an effective classical XY model. The ground state at intermediate correlations is consistently shown to be a chiral Mott insulator (CMI) with a gap to all excitations and staggered loop currents which spontaneously break time reversal symmetry. We characterize the CMI state as a vortex supersolid or an indirect exciton condensate, and discuss various experimental implications.