The relationship between transport anisotropy and nematicity in FeSe

TL;DR

This study investigates how large elastic strains influence nematicity and resistive anisotropy in FeSe, revealing a peak and sign change in anisotropy and highlighting the role of stress and orbital effects in nematic behavior.

Contribution

It demonstrates the effects of large elastic strains on nematicity in FeSe and clarifies the conjugate field as stress rather than strain, providing new insights into nematic mechanisms.

Findings

Resistive anisotropy peaks at about 7% as nematicity increases.

Below ~40 K, the nematic resistive anisotropy reverses sign.

Biaxial compression raises resistivity and superconducting Tc.

Abstract

The mechanism behind the nematicity of FeSe is not known. Through elastoresitivity measurements it has been shown to be an electronic instability. However, so far measurements have extended only to small strains, where the response is linear. Here, we apply large elastic strains to FeSe, and perform two types of measurements. (1) Using applied strain to control twinning, the nematic resistive anisotropy at temperatures below the nematic transition temperature Ts is determined. (2) Resistive anisotropy is measured as nematicity is induced through applied strain at fixed temperature above Ts. In both cases, as nematicity strengthens the resistive anisotropy peaks about about 7%, then decreases. Below ~40 K, the nematic resistive anisotropy changes sign. We discuss possible implications of this behaviour for theories of nematicity. We report in addition: (1) Under experimentally accessible conditions with bulk crystals, stress, rather than strain, is the conjugate field to the nematicity of FeSe. (2) At low temperatures the twin boundary resistance is ~10% of the sample resistance, and must be properly subtracted to extract intrinsic resistivities. (3) Biaxial inplane compression increases both in-plane resistivity and the superconducting critical temperature Tc, consistent with a strong role of the yz orbital in the electronic correlations.