Impurity-Induced Electronic Nematic State in Iron-Pnictide Superconductors

TL;DR

This paper proposes that impurities induce an electronic nematic state in iron-pnictide superconductors above the structural transition temperature, revealing strong orbital fluctuations and explaining observed resistivity anisotropy.

Contribution

It demonstrates that impurities can induce non-local orbital order with C2 symmetry above T_S, supported by theoretical analysis and experimental observations.

Findings

Impurity-induced orbital order aligns along the a-axis under uniaxial pressure.

Resistivity shows in-plane anisotropy ($\rho_b/\rho_a \sim 2$) above T_S.

Strong orbital fluctuations are present in iron-pnictide superconductors.

Abstract

We propose that impurity-induced electronic nematic state is realized above the orthorhombic structure transition temperature $T_S$ in iron-pnictide superconductors. In the presence of strong orbital fluctuations near $T_S$, it is theoretically revealed that a single impurity induces non-local orbital order with $C_2$-symmetry, consistently with recent STM/STS measurements. Each impurity-induced $C_2$ orbital order aligns along a-axis by applying tiny uniaxial pressure along b-axis. In this impurity-induced nematic phase, the resistivity shows sizable in-plane anisotropy ($\rho_b/\rho_a \sim 2$) even above $T_S$, actually observed in various "detwinned" samples. The present study indicates the existence of strong orbital fluctuations in iron-pnictide superconductors.