# Pair hopping in systems of strongly interacting hard-core bosons

## TL;DR

This study uses quantum Monte Carlo simulations to explore how pair-hopping processes influence the phase diagram of strongly interacting hard-core bosons on a square lattice, revealing their role in destabilizing Mott phases.

## Contribution

It introduces the effect of pair hopping in the hard-core boson model and demonstrates its impact on the stability of Mott phases, a novel aspect not previously analyzed.

## Key findings

- Pair hopping destabilizes Mott phases at certain fillings.
- Different Mott phases melt at different pair-hopping amplitudes.
- Pair hopping influences the competition between superfluid, insulating, and supersolid phases.

## Abstract

We have used the Stochastic Series Expansion quantum Monte Carlo method to study interacting hard-core bosons on the square lattice, with pair-hopping processes supplementing the standard single-particle hopping. Such pair hopping arises in effective models for frustrated quantum magnets. Our goal is to investigate the effects of the pair hopping process on the commonly observed superfluid, insulating (Mott), and super-solid ground-state phases in the standard hard-core boson model with various interaction terms. The model is specifically motivated by the observation of finite dispersion of 2-magnon bound states in neutron diffraction experiments SrCu$_2$(BO$_3$)$_2$. Our results show that the pair hopping has different effects on Mott phases at different filling fractions, "melting" them at different critical pair-hopping amplitudes. Thus, it appears that pair hopping may have an important role in determining which out of a potentially large number of Mott phases (stabilized by details of the charge-diagonal interaction terms) actually survive the totality of quantum fluctuations present.