Impairment of double exchange mechanism in electron transport of iron pnictides

TL;DR

This paper investigates why the double exchange mechanism fails to explain resistivity anisotropy in iron pnictides, highlighting the roles of orbital ordering, Hund's coupling, and second neighbor hoppings in electron transport.

Contribution

It identifies key microscopic factors, especially orbital ordering and second neighbor hoppings, that influence electron transport beyond the traditional double exchange model in iron pnictides.

Findings

Orbital ordering explains resistivity anisotropy trends.

Second neighbor hoppings oppose double exchange effects.

Orbital degrees of freedom are crucial in electron transport.

Abstract

Double exchange mechanism is believed to favor transport along ferromagnetic directions, the failure of which in explaining the unusual resistivity anisotropy in iron pnictides is investigated. Several factors intrinsic to the microscopic mechanism of transport in iron pnictides are identified and analyzed, including the moderate Hund's coupling, low local moment, and presence of two anisotropic degenerate orbitals xz and yz. In particular, the substantial second neighbor hoppings are found to be decisive in giving results opposite to the double exchange picture. In high temperature nonmagnetic phase, orbital ordering is shown to give the right trend of resistivity anisotropy as observed experimentally, advocating its essential role in electron transport of iron pnictides.