Vestigial chiral and charge orders from bidirectional spin-density waves: Application to the iron-based superconductors

TL;DR

The paper explores how certain magnetic phases in iron-based superconductors can undergo two-stage melting, leading to vestigial charge and spin orders that influence superconductivity and are experimentally detectable.

Contribution

It introduces the concept of vestigial charge and spin orders emerging from the melting of bidirectional spin-density waves in iron-based superconductors, with specific predictions for experimental signatures.

Findings

Intermediate vestigial phases with charge and spin order parameters.

Enhanced superconducting transition temperature due to fluctuations.

Proposed experimental signatures for detecting these vestigial orders.

Abstract

Recent experiments in optimally hole-doped iron arsenides have revealed a novel magnetically ordered ground state that preserves tetragonal symmetry, consistent with either a charge-spin density wave (CSDW), which displays a non-uniform magnetization, or a spin-vortex crystal (SVC), which displays a non-collinear magnetization. Here we show that, similarly to the partial melting of the usual stripe antiferromagnet into a nematic phase, either of these phases can also melt in two stages. As a result, intermediate paramagnetic phases with vestigial order appears: a checkerboard charge density-wave for the CSDW ground state, characterized by an Ising-like order parameter, and a remarkable spin-vorticity density-wave for the SVC ground state -- a triplet d-density wave characterized by a vector chiral order parameter. We propose experimentally detectable signatures of these phases, show that their fluctuations can enhance the superconducting transition temperature, and discuss their relevance to other correlated materials.