Orbital multicriticality in spin gapped quasi-1D antiferromagnets

TL;DR

This paper investigates spin-orbital interactions in quasi-1D antiferromagnets, revealing gapless orbital liquid phases and a multicritical point leading to coexisting orbital order, using simplified models and field theory analysis.

Contribution

It introduces a simplified model showing gapless orbital liquids without strict orbital symmetry and analyzes multicritical behavior in CaV$_2$O$_4$-like systems.

Findings

Gapless orbital liquid phases with power-law correlations.

Emergence of coexisting orbital order near multicritical points.

Phase diagram constructed using field theory and exact solutions.

Abstract

Motivated by the quasi-1D antiferromagnet CaV$_2$O$_4$, we explore spin-orbital systems in which the spin modes are gapped but orbitals are near a macroscopically degenerate classical transition. Within a simplified model we show that gapless orbital liquid phases possessing power-law correlations may occur without the strict condition of a continuous orbital symmetry. For the model proposed for CaV$_2$O$_4$, we find that an orbital phase with coexisting order parameters emerges from a multicritical point. The effective orbital model consists of zigzag-coupled transverse field Ising chains. The corresponding global phase diagram is constructed using field theory methods and analyzed near the multicritical point with the aid of an exact solution of a zigzag XXZ model.