Chiral Bosonic Mott Insulator on the Frustrated Triangular Lattice

TL;DR

This paper investigates the emergence of a chiral Mott insulator phase in frustrated bosonic systems on a triangular lattice, revealing novel symmetry-breaking and current order phenomena through theoretical and numerical methods.

Contribution

It introduces the chiral Mott insulator phase resulting from frustrated hopping, combining variational, bosonization, and DMRG techniques for phase diagram analysis.

Findings

Identification of chiral Mott insulator with current order

Superfluid instability leads to chiral order at nonzero wavevector

Potential experimental signatures in optical lattices

Abstract

We study the superfluid and insulating phases of interacting bosons on the triangular lattice with an inverted dispersion, corresponding to frustrated hopping between sites. The resulting single-particle dispersion has multiple minima at nonzero wavevectors in momentum space, in contrast to the unique zero-wavevector minimum of the unfrustrated problem. As a consequence, the superfluid phase is unstable against developing additonal chiral order that breaks time reversal (T) and parity (P) symmetries by forming a condensate at nonzero wavevector. We demonstrate that the loss of superfluidity can lead to an even more exotic phase, the chiral Mott insulator, with nontrivial current order that breaks T, P. These results are obtained via variational estimates, as well as a combination of bosonization and DMRG of triangular ladders, which taken together permit a fairly complete characterization of the phase diagram. We discuss the relevance of these phases to optical lattice experiments, as well as signatures of chiral symmetry breaking in time-of-flight images.