Landau Theory of Stripe Phases in Cuprates and Nickelates

TL;DR

This paper develops a Landau theory model for stripe phases in cuprates and nickelates, explaining experimental observations of charge and spin orderings and predicting possible spiral magnetic phases.

Contribution

It introduces a coupled charge and spin-density wave Landau theory that distinguishes charge-driven from spin-driven orderings and predicts non-collinear spiral phases.

Findings

Charge density wave period is half that of spin density wave.

Charge-driven orderings match experimental transition sequences.

Spiral spin phases are possible in spin-driven regions with elliptical spin order.

Abstract

We consider a Landau theory of coupled charge and spin-density wave order parameters as a simple model for the ordering that has been observed experimentally in the La_2NiO_4 and La_2CuO_4 families of doped antiferromagnets. The period of the charge-density wave is generically half that of the spin-density wave, or equivalently the charges form antiphase domain walls in the antiferromagnetic order. A sharp distinction exists between the case in which the ordering is primarily charge driven (which produces a sequence of transitions in qualitative agreement with experiment) or spin driven (which does not). We also find that stripes with non-collinear spin order (i.e. spiral phases) are possible in a region of the phase diagram where the transition is spin driven; the spiral is circular only when there is no charge order, and is otherwise elliptical with an eccentricity proportional to the magnitude of the charge order.