The Nonintrinsic Sector of Landau Theory

TL;DR

This paper introduces a nonintrinsic sector in Landau theory where external microscale fields influence the free-energy functional, expanding the traditional understanding of fixed thermodynamic parameters.

Contribution

It demonstrates how externally imposed microscale fields can persist through coarse graining and affect Landau free-energy coefficients, revealing a new sector of the theory.

Findings

External fields can survive coarse graining in Landau theory.

Ion-patterned FeRh is a plausible realization of this nonintrinsic sector.

Hierarchy of length scales is key to this phenomenon.

Abstract

Landau theory usually treats free-energy coefficients as intrinsic parameters fixed by thermodynamic variables. We show that externally written microscale fields can survive coarse graining and enter the free-energy functional as spatially prescribed coefficient fields. This defines a nonintrinsic sector of Landau theory. The key condition is a hierarchy of correlation, writing, and frustration lengths. We identify ion-patterned FeRh as a plausible realization.