Discovery of mesoscopic nematicity wave in iron-based superconductors

TL;DR

This paper reports the discovery of mesoscopic sinusoidal waves of electronic nematicity in iron-based superconductors, revealing a long-range coherence of the nematic order parameter through direct real-space visualization.

Contribution

It introduces the first direct real-space imaging of mesoscopic nematicity waves in IBSCs, showing an unexpectedly long coherence length of the nematic order.

Findings

Nematicity exhibits sinusoidal wave patterns with mesoscopic wavelength.

The nematic order has a coherence length over 1000 times the lattice constant.

Direct visualization uncovers a new aspect of quantum liquid crystalline states.

Abstract

Nematicity is ubiquitous in electronic phases of high transition temperature superconductors, particularly in iron-based superconductors (IBSCs). Order parameter that characterizes the nematic phase has been investigated in momentum space, but its real-space arrangement remains largely unclear. We use linear dichroism (LD) in low-temperature laser-photoemission electron microscope to map out the nematic order parameter of nonmagentic FeSe and antiferromagnetic BaFe2(As0.87P0.13)2. In contrast to the structural domains that have atomic-scale domain walls, the LD patterns in both materials show peculiar sinusoidal waves of electronic nematicity with mesoscopic wavelength. The analysis reveals that the nematic order has an extremely long coherence length, more than 1000 times longer than the unit cell. Our direct visualization of electronic spatial variation uncovers a new fundamental aspect of quantum liquid crystalline states of correlated electrons in IBSCs.