Doped Singlet-Pair Crystal in the Hubbard model on the checkerboard lattice

TL;DR

This paper explores the Hubbard model on the checkerboard lattice, revealing a novel insulating phase at quarter-filling and examining how doping affects phase separation and potential superconductivity.

Contribution

It introduces the Resonating Singlet-Pair Crystal as a new quantum state and analyzes doping effects, highlighting differences from quantum antiferromagnets.

Findings

Discovery of the Resonating Singlet-Pair Crystal phase.

Restricted phase separation for small hopping.

Fragile superconducting pairing at large hopping.

Abstract

In the limit of large nearest--neighbor and on--site Coulomb repulsions, the Hubbard model on the planar pyrochlore lattice maps, near quarter-filling, onto a doped quantum fully packed loop model. The phase diagram exhibits at quarter filling a novel quantum state of matter, the Resonating Singlet-Pair Crystal, an insulating phase breaking lattice symmetry. Properties of a few doped holes are investigated. In contrast to the doped quantum antiferromagnet, phase separation is restricted to very small hopping leaving an extended``window'' for superconducting pairing. However the later is more fragile for large hopping than in the case of the antiferromagnet.