Phase diagram of a 1 dimensional spin-orbital model

TL;DR

This paper investigates the phase diagram of a one-dimensional spin-orbital model using analytical and numerical methods, revealing a previously overlooked gapless phase with SU(4) symmetry and characterizing the phase transition to a gapped phase.

Contribution

It identifies an extended gapless phase with SU(4) symmetry near an integrable point, and characterizes the phase transition as a generalized Kosterlitz-Thouless transition.

Findings

Existence of a gapless SU(4) invariant phase

Different velocities for spin and orbital excitations

Phase transition in a generalized Kosterlitz-Thouless universality class

Abstract

We study a 1 dimensional spin-orbital model using both analytical and numerical methods. Renormalization group calculations are performed in the vicinity of a special integrable point in the phase diagram with SU(4) symmetry. These indicate the existence of a gapless phase in an extended region of the phase diagram, missed in previous studies. This phase is SU(4) invariant at low energies apart from the presence of different velocities for spin and orbital degrees of freedom. The phase transition into a gapped dimerized phase is in a generalized Kosterlitz-Thouless universality class. The phase diagram of this model is sketched using the density matrix renormalization group technique.