Anisotropic electrical resistivity of LaFeAsO: evidence for electronic nematicity

TL;DR

This study measures the anisotropic electrical resistivity of LaFeAsO single crystals, revealing in-plane anisotropy above structural transition temperature, indicating electronic nematicity, and observes a magnetic structure change at low temperature.

Contribution

It provides direct experimental evidence for electronic nematicity in LaFeAsO through anisotropic resistivity measurements and advanced fabrication techniques.

Findings

In-plane resistivity anisotropy observed above structural transition temperature.

Evidence for electronic nematic phase formation.

Magnetic structure changes from antiferromagnetic to ferromagnetic at 11 K.

Abstract

Single crystals of LaFeAsO were successfully grown out of KI flux. Temperature dependent electrical resistivity was measured with current flow along the basal plane, \rho_perpend(T), as well as with current flow along the crystallographic c-axis, \rho_parallel(T), the latter one utilizing electron beam lithography and argon ion beam milling. The anisotropy ratio was found to lie between \rho_parallel/\rho_perpend = 20 - 200. The measurement of \rho_perpend(T) was performed with current flow along the tetragonal [1 0 0] direction and along the [1 1 0] direction and revealed a clear in-plane anisotropy already at T \leq 175 K. This is significantly above the orthorhombic distortion at T_0 = 147 K and indicates the formation of an electron nematic phase. Magnetic susceptibility and electrical resistivity give evidence for a change of the magnetic structure of the iron atoms from antiferromagnetic to ferromagnetic arrangement along the c-axis at T^\ast = 11 K.