The mobility of dual vortices in honeycomb, square, triangular, Kagome and dice lattices

TL;DR

This paper investigates the Hofstadter bands of vortices in various lattices, revealing exponential decay of bandwidths and flat bands at specific flux values, with implications for boson ground states in these lattices.

Contribution

It provides a detailed numerical analysis of Hofstadter bands for vortices on five common lattices, including bandwidth decay laws and flat band conditions at specific flux values.

Findings

Bandwidths generally decay exponentially with flux denominator q.

At q=2, Kagome and dice lattices have flat lowest Hofstadter bands.

Flat bands at q=2 suggest superfluid ground states in Kagome and dice lattices.

Abstract

It was known that by a duality transformation, interaction bosons at filling factor $ f=p/q $ hopping on a lattice can be mapped to interacting vortices hopping on the dual lattice subject to a fluctuating{\em dual} " magnetic field" whose average strength through a dual plaquette is equal to the boson density $ f=p/q $.So the kinetic term of the vortices is the same as the Hofstadter problem of electrons moving in a lattice in the presence of $ f=p/q $ flux per plaquette. Motivated by this mapping, we study the Hofstadter bands of vortices hopping in the presence of magnetic flux $ f=p/q $ per plaquette on 5 most common bi-partisian and frustrated lattices such as square, honeycomb, triangular, dice and Kagome lattices. We also determine the number of minima and their locations in the lowest band. We numerically calculate the bandwidths of the lowest Hofstadter bands in these lattices and find that except the Kagome lattice at odd $ q $, they all satisfy the exponential decay law $ W = A e^{-cq} $ even at the smallest $ q $. We determine $ (A, c) $ for the 5 different lattices. When $ q=2 $, we find that the lowest Hofstadter band is completely flat for both Kagome and dice lattices. This indicates that the boson ground state at half filling with nearest neighbor hopping on Kagome and dice lattice is always a superfluid state,in contrast to the triangular lattice where the boson ground state was shown previously to undergo a transition from superfluid to supersolid state.