Visualizing the Nonlinear Coupling between Strain and Electronic Nematicity in the Iron Pnictides by Elasto-Scanning Tunneling Spectroscopy

TL;DR

This paper introduces a novel spectroscopic technique with atomic resolution to study how anisotropic strain influences electronic nematicity in iron-based superconductors, revealing persistent nematic fluctuations and strong nonlinear coupling effects.

Contribution

It presents a new elasto-scanning tunneling spectroscopy method to quantitatively analyze strain-induced electronic anisotropy and nematic fluctuations in quantum materials.

Findings

Nematic fluctuations persist above the structural transition temperature.

Uniaxial strain significantly enhances nematic fluctuation amplitude.

Strong nonlinear coupling between strain and electronic nematicity is observed.

Abstract

Mechanical strain is a powerful technique for tuning electronic structure and interactions in quantum materials. In a system with tetragonal symmetry, a tunable uniaxial in-plane strain can be used to probe nematic correlations in the same way that a tunable magnetic field is used to probe magnetic correlations. Here, we present a new spectroscopic scanned probe technique that provides atomic-resolution insight into the effect of anisotropic strain on the electronic structure. We use this technique to study nematic fluctuations and nematic order across the phase diagram of a prototypical iron-based superconductor. By extracting quantitatively the electronic anisotropy as function of applied strain, we show that while true long range nematic order is established at the tetragonal to orthorhombic structural transition temperature, sizable nematic fluctuations persist to high temperatures and also to the overdoped end of the superconducting dome. Remarkably, we find that uniaxial strain in the pnictides significantly enhances the amplitude of the nematic fluctuations, indicating a strong nonlinear coupling between structure and electronic nematicity.