Alternating Spin and Orbital Dimerization in Strong-coupling Two-band Models

TL;DR

This paper investigates a one-dimensional coupled spin and orbital model, revealing complex phases including gapless lines and a gapped phase with alternating singlet formations, using advanced numerical methods.

Contribution

It introduces a detailed phase diagram of a coupled spin-orbital model and identifies a novel gapped phase with alternating singlet states.

Findings

Identification of a gapless line connecting ferromagnetic and SU(4) critical points.

Discovery of a gapped phase with alternating spin and orbital singlets.

Relevance to recently discovered spin-gap materials.

Abstract

We study a one-dimensional Hamiltonian consisting of coupled SU(2) spin and orbital degrees of freedom. Using the density matrix renormalization group, we calculate the phase-diagram and the ground state correlation functions for this model. We find that, in addition to the ferromagnetic and power-law antiferromagnetic phases for spin and orbital degrees of freedom, this model has a gapless line extending from the ferromagnetic phase to the Bethe ansatz solvable SU(4) critical point, and a gapped phase with doubly degenerate ground states which form alternating spin and orbital singlets. The spin-gap and the order parameters are evaluated and the relevance to several recently discovered spin-gap materials is discussed.