Two-band electronic metal and neighboring spin liquid (spin Bose-metal) on a zigzag strip with longer-ranged repulsion

TL;DR

This paper explores how extended electronic interactions on a zigzag strip can stabilize a spin Bose-metal phase, a type of spin liquid, by analyzing a two-band metal model with renormalization group and bosonization techniques.

Contribution

It demonstrates that extended repulsion broadens the metallic phase and facilitates the emergence of the spin Bose-metal phase in a two-band electronic model.

Findings

Extended interactions expand the C2S2 metallic phase.

An eight-fermion Umklapp term induces a Mott insulator.

The spin Bose-metal phase naturally arises with increased repulsion.

Abstract

We consider an electronic model for realizing the Spin Bose-metal (SBM) phase on a 2-leg triangular strip --a spin liquid phase found by D. N. Sheng et al [Phys. Rev. B {\bf 79}, 205112 (2009)] in a spin-1/2 model with ring exchanges. The SBM can be viewed as a "C1S2" Mott insulator of electrons where the overall charge transporting mode is gapped out. We start from a two-band "C2S2" metal and consider extended repulsion motivated by recent ab initio derivation of electronic model for $\kappa$-ET spin liquid material [K. Nakamura et al, J. Phys. Soc. Jpn. {\bf 78}, 083710(2009)]. Using weak coupling renormalization group analysis, we find that the extended interactions allow much wider C2S2 metallic phase than in the Hubbard model with on-site repulsion only. An eight-fermion Umklapp term plays a crucial role in producing a Mott insulator but can not be treated in weak coupling. We use Bosonization to extend the analysis to intermediate coupling and study phases obtained out of the C2S2 metal upon increasing overall repulsion strength, finding that the SBM phase is a natural outcome for extended interactions.