Discovery of a strain-stabilised smectic electronic order in LiFeAs

TL;DR

This study reveals how strain induces a novel smectic electronic order in LiFeAs, transitioning from superconductivity to a symmetry-broken phase with reduced rotational and translational symmetry.

Contribution

It demonstrates the direct observation of strain-stabilized smectic order in LiFeAs, linking lattice distortions to complex electronic phases.

Findings

Strain stabilizes a smectic electronic phase in LiFeAs.

Superconductivity is suppressed as the material transitions to the smectic phase.

Electronic symmetry breaking correlates with lattice distortions.

Abstract

In many high temperature superconductors, small orthorhombic distortions of the lattice structure result in surprisingly large symmetry breaking of the electronic states and macroscopic properties, an effect often referred to as nematicity. To directly study the impact of symmetry-breaking lattice distortions on the electronic states, using low-temperature scanning tunnelling microscopy we image at the atomic scale the influence of strain-tuned lattice distortions on the correlated electronic states in the iron-based superconductor LiFeAs, a material which in its ground state is tetragonal, with four-fold ($C_4$) symmetry. Our experiments uncover a new strain-stabilised modulated phase which exhibits a smectic order in LiFeAs, an electronic state which not only breaks rotational symmetry but also reduces translational symmetry. We follow the evolution of the superconducting gap from the unstrained material with $C_4$ symmetry through the new nematic phase with two-fold ($C_2$) symmetry and charge-density-wave order to a state where superconductivity is completely suppressed.