Random-strain-induced correlations in materials with intertwined nematic and magnetic orders

TL;DR

This paper introduces a novel random Baxter-field model to simulate the effects of random strain on intertwined nematic and magnetic orders in correlated materials, revealing disorder-induced magnetic correlations and domain structures.

Contribution

It develops a new theoretical model capturing the dual role of random strain in nematic systems with intertwined magnetic orders, extending beyond traditional models.

Findings

Random strain causes nematic domain breakup.

Disorder promotes nontrivial magnetic correlations.

Magnetic noise spectrum shows characteristic signatures.

Abstract

Electronic nematicity is rarely observed as an isolated instability of a correlated electron system. Instead, in iron pnictides and in certain cuprates and heavy-fermion materials, nematicity is intertwined with an underlying spin-stripe or charge-stripe state. As a result, random strain, ubiquitous in any real crystal, creates both random-field disorder for the nematic degrees of freedom and random-bond disorder for the spin or charge ones. Here, we put forward an Ashkin-Teller model with random Baxter fields to capture the dual role of random strain in nematic systems for which nematicity is a composite order arising from a stripe state. Using Monte Carlo to simulate this $\textit{random Baxter-field model}$, we find not only the expected break-up of the system into nematic domains, but also the emergence of nontrivial disorder-promoted magnetic correlations. Such correlations enhance and tie up the fluctuations associated with the two degenerate magnetic stripe states from which nematicity arises, leaving characteristic signatures in the spatial profile of the magnetic domains, in the configurational space of the spin variables, and in the magnetic noise spectrum. We discuss possible experimental manifestations of these effects in iron-pnictide superconductors. Our work establishes the random Baxter-field model as a more complete alternative to the random-field Ising model to describe complex electronic nematic phenomena in the presence of disorder.