Extended Coulomb liquid of paired hardcore boson model on a pyrochlore lattice

Abstract

There is growing interest in the U(1) Coulomb liquid in both quantum materials in pyrochlore ice and cluster Mott insulators and cold-atom systems. We explore a paired hardcore boson model on a pyrochlore lattice. This model is equivalent to the XYZ spin model that was proposed for rare-earth-metal pyrochlores with 'dipole-octupole' doublets. Since our model has no sign problem for quantum Monte Carlo (QMC) simulations in a large parameter regime, we carry out both analytical and QMC calculations. We find that the U(1) Coulomb liquid is quite stable and spans a rather large portion of the phase diagram with boson pairing. Moreover, we numerically find a thermodynamic evidence that the boson pairing could induce a possible Z(2) liquid in the vicinity of the phase boundary between Coulomb liquid and Z(2) symmetry-broken phase. Besides the materials' relevance with quantum spin ice, we point to quantum simulation with cold atoms on optical lattices.