Effect of symmetry breaking perturbations in the one-dimensional SU(4) spin-orbital model

TL;DR

This paper investigates how symmetry-breaking perturbations affect the low-energy physics of the one-dimensional SU(4) spin-orbital model, revealing new scaling behaviors and phase transitions induced by anisotropy and magnetic fields.

Contribution

The study extends the analysis of the SU(4) spin-orbital model to include anisotropic exchange interactions and magnetic fields, uncovering novel phase transitions and effective theories.

Findings

Massless behavior persists in large anisotropic regions.

Anisotropy induces non-trivial scaling behaviors.

Magnetic field causes additional phase transitions, including a KT transition.

Abstract

We study the effect of symmetry breaking perturbations in the one-dimensional SU(4) spin-orbital model. We allow the exchange in spin ($J_1$) and orbital ($J_2$) channel to be different and thus reduce the symmetry to SU(2) $\otimes$ SU(2). A magnetic field $h$ along the $S^z$ direction is also applied. Using the formalism developped by Azaria et al we extend their analysis of the isotropic $J_1=J_2$, h=0 case and obtain the low-energy effective theory near the SU(4) point in the asymmetric case. An accurate analysis of the renormalization group flow is presented with a particular emphasis on the effect of the anisotropy. In zero magnetic field, we retrieve the same qualitative low-energy physics than in the isotropic case. In particular, the massless behavior found on the line $J_1=J_2>K/4$ extends in a large anisotropic region. We discover though that the anisotropy plays its trick in allowing non trivial scaling behaviors of the physical quantities. When a magnetic field is present the effect of the anisotropy is striking. In addition to the usual commensurate-incommensurate phase transition that occurs in the spin sector of the theory, we find that the field may induce a second transition of the KT type in the remaining degrees of freedom to which it does not couple directly. In this sector, we find that the effective theory is that of an SO(4) Gross-Neveu model with an h-dependent coupling that may change its sign as h varies.