Insulating spin liquid in the lightly doped two-dimensional Hubbard model

TL;DR

This paper uses a two-loop renormalization group approach to show that the lightly doped 2D Hubbard model may exhibit an insulating spin liquid state due to gaps opening in charge and spin spectra at intermediate interactions.

Contribution

It introduces a two-loop RG analysis revealing the possibility of an insulating spin liquid phase in the lightly doped 2D Hubbard model, contrasting with the traditional Mott insulator.

Findings

Charge and spin susceptibilities flow to zero at intermediate couplings.

Gaps open in charge and spin excitation spectra.

Ground state may be an insulating spin liquid rather than a Mott insulator.

Abstract

We calculate the charge compressibility and uniform spin susceptibility for the two-dimensional (2D) Hubbard model slightly away from half-filling within a two-loop renormalization group scheme. We find numerically that both those quantities flow to zero as we increase the initial interaction strength from weak to intermediate couplings. This result implies gap openings in both charge and spin excitation spectra for the latter interaction regime. When this occurs, the ground state of the lightly doped 2D Hubbard model may be interpreted as an insulating spin liquid as opposed to a Mott insulating state.