Defect-induced electronic smectic state at the surface of nematic materials

TL;DR

This paper demonstrates that surface defects in nematic materials induce an incommensurate smectic phase localized at the surface, explaining recent experimental observations of modulated nematic states and pre-transitional signatures.

Contribution

It reveals how surface defects cause a shift in the nematic instability wave-vector, leading to a surface smectic phase above the bulk transition temperature.

Findings

Defects induce a non-zero wave-vector of the nematic instability.

Surface smectic phase appears above the bulk nematic transition.

Explains experimental signatures of nematic order prior to structural distortion.

Abstract

Due to the intertwining between electronic nematic and elastic degrees of freedom, lattice defects and structural inhomogeneities commonly found in crystals can have a significant impact on the electronic properties of nematic materials. Here, we show that defects commonly present at the surface of crystals generally shift the wave-vector of the nematic instability to a non-zero value, resulting in an incommensurate electronic smectic phase. Such a smectic state onsets above the bulk nematic transition temperature and is localized near the surface of the sample. We argue that this effect may explain not only recent observations of a modulated nematic phase in iron-based superconductors, but also several previous puzzling experiments that reported signatures consistent with nematic order before the onset of a bulk structural distortion.