Intrinsic translational symmetry-breaking charge stripes in underdoped iron pnictides

TL;DR

This study uncovers intrinsic unidirectional charge stripe order in underdoped iron pnictides, linking nematicity and superconductivity, and demonstrating charge order as a common feature in high-temperature superconductors.

Contribution

It provides the first direct spectroscopic evidence of intrinsic charge-stripe order in iron pnictides, revealing its role as an intermediate phase between nematicity and superconductivity.

Findings

Charge stripes are unidirectional and near-commensurate.

Charge order correlates with a van Hove singularity near the Fermi level.

Suppressing charge order enhances superconductivity.

Abstract

Despite being well established in cuprates, an intrinsic translational symmetry-breaking charge order has not been clearly identified in iron-based superconductors. Using spectroscopic-imaging scanning tunneling microscopy on epitaxial Ca(Fe1-xCox)2As2 (x = 0 ~ 0.055) thin films, we observe smectic, near-commensurate charge-stripe order in the underdoped regime that intervenes between the nematic parent phase and optimally doped superconductivity. Distinct from the bidirectional checkerboard-like order in cuprates, these charge stripes are unidirectional along the antiferromagnetic Fe-Fe bond direction and are accompanied by a van Hove singularity near the Fermi level, inherited from the Fermi surface reconstruction driven by intertwined antiferromagnetic and nematic correlations. Both local and global suppression of the charge-stripe instability enhance superconductivity, tunable via epitaxial strain and Co doping. These results establish charge-stripe order as an intermediate electronic phase in iron pnictides and reveal a coherent pathway from nematicity to superconductivity. Our findings highlight charge ordering as a unifying element across different families of high-temperature superconductors.