Spin Bose-Metal and Valence Bond Solid phases in a spin-1/2 model with ring exchanges on a four-leg triangular ladder

TL;DR

This paper investigates a spin-1/2 model with ring exchanges on a four-leg triangular ladder, revealing a spin Bose-metal phase, a staggered dimer phase, and a rung phase, and discusses potential two-dimensional phase diagrams.

Contribution

It introduces a detailed analysis of phase transitions in a spin-1/2 ring exchange model using DMRG and variational methods, highlighting the existence of a spin Bose-metal phase.

Findings

Identification of a spin Bose-metal phase with a spinon Fermi sea.

Discovery of a staggered dimer phase near the square lattice regime.

Observation of a featureless rung phase at small ring exchanges.

Abstract

We study a spin-1/2 system with Heisenberg plus ring exchanges on a four-leg triangular ladder using the density matrix renormalization group and Gutzwiller variational wave functions. Near an isotropic lattice regime, for moderate to large ring exchanges we find a spin Bose-metal phase with a spinon Fermi sea consisting of three partially filled bands. Going away from the triangular towards the square lattice regime, we find a staggered dimer phase with dimers in the transverse direction, while for small ring exchanges the system is in a featureless rung phase. We also discuss parent states and a possible phase diagram in two dimensions.