Hidden string order in a hole-superconductor with extended correlated hopping

TL;DR

This paper investigates a one-dimensional Hubbard model with extended correlated hopping in ultracold fermions, revealing hidden string order, spin-charge separation, and a persistent spin-gap through exact solutions and numerical studies.

Contribution

It provides an exact solution for a special correlated hopping value and demonstrates the robustness of string order and spin-gap away from integrability.

Findings

Exact and asymmetric spin-charge separation

Presence of a spin-gap related to hole pairing

Persistence of string order away from the integrable point

Abstract

Ultracold fermions in a one-dimensional, spin-dependent, optical lattice are described by a non-standard Hubbard model with next-nearest-neighbour correlated hopping. Periodic driving of the lattice allows wide tuning of the system parameters. We solve this model exactly for a special value of the correlated hopping. The solution reveals the general properties of this system for arbitrary filling: exact and asymmetric spin-charge separation, a gapless spectrum of lowest energy excitations, a spin-gap, which may be interpreted in terms of collective hole pairing and a non-vanishing den Nijs-Rommelse type string correlator. Numerical studies away from the integrable point show the persistence of both long range string order and spin-gap.