Single-particle versus pair condensation of hard-core bosons with correlated hopping

TL;DR

This study explores how correlated hopping influences the ground state of hard-core bosons on a square lattice, revealing a novel low-density pairing phase with long-range two-particle correlations, challenging standard simulation methods.

Contribution

It demonstrates that modest nearest-neighbor repulsion suppresses phase separation and induces a pairing phase without single-particle BEC in hard-core bosons with correlated hopping.

Findings

Correlated hopping induces phase separation in non-interacting hard-core bosons.

Nearest-neighbor repulsion suppresses phase separation.

A low-density pairing phase with long-range two-particle correlations emerges.

Abstract

We investigate the consequences of correlated hopping on the ground state properties of hard-core bosons on a square lattice as revealed by extensive exact diagonalizations and quantum Monte Carlo simulations. While for non interacting hard-core bosons the effective attraction induced by the correlated hopping leads to phase separation at low density, we show that a modest nearest-neighbor repulsion suppresses phase separation, leading to a remarkable low-density pairing phase with no single particle Bose-Einstein condensation but long-range two-particle correlations, signaling a condensation of pairs. We also explain why the unusual properties of the pairing phase are a real challenge for standard one-worm quantum Monte Carlo simulations.