Superconductivity from doping a spin liquid insulator: a simple one-dimensional example

TL;DR

This paper investigates a one-dimensional Hubbard model with next-nearest neighbor hopping, revealing a doping-induced transition from magnetic insulator to a superconducting phase with a spin gap, despite repulsive interactions.

Contribution

It introduces a detailed phase diagram of a 1D Hubbard model with next-nearest neighbor hopping, highlighting a novel doping-induced superconducting phase.

Findings

Doping a magnetic insulator leads to a metallic phase with a spin gap.

Superconducting fluctuations dominate in the doped phase.

Superconductivity can be achieved through hole doping of the magnetic insulator.

Abstract

We study the phase diagram of a one-dimensional Hubbard model where, in addition to the standard nearest neighbor hopping $t$, we also include a next-to-nearest neighbor hopping $t'$. For strong enough on-site repulsion, this model has a transition at half filling from a magnetic insulator with gapless spin excitations at small $t'/t$ to a dimerized insulator with a spin gap at larger $t'/t$. We show that upon doping this model exhibits quite interesting features, which include the presence of a metallic phase with a spin gap and dominant superconducting fluctuations, in spite of the repulsive interaction. More interestingly, we find that this superconducting phase can be reached upon hole doping the magnetic insulator. The connections between this model and the two chain models, recently object of intensive investigations, are also discussed.