Transport and infrared properties of SmFeAs(O1-xFx): from SDW to superconducting ordering

TL;DR

This study investigates the electronic and infrared properties of SmFeAsO and doped SmFeAs(O0.93F0.07), revealing how doping suppresses magnetic order and promotes superconductivity by altering Fermi surface symmetries.

Contribution

It provides a detailed experimental analysis of the transition from spin density wave order to superconductivity in SmFeAsO-based compounds, highlighting the role of doping in Fermi surface symmetry breaking.

Findings

SDW signatures are present in undoped SmFeAsO.

Doping suppresses SDW and induces superconductivity.

Electronic properties show minimal change in density of states upon doping.

Abstract

We report measurements of resistivity, magnetoresistivity, Hall effect, Seebeck coefficient, infrared reflectivity of undoped SmFeAsO and lightly doped SmFeAs(O0.93F0.07) oxypnictides. All the properties measured on SmFeAsO are characterized by clear signatures of the magnetic instability. A self-consistent picture emerges in which below the magnetic transition carrier condensation occurs due to the opening of spin density wave (SDW) gap. This is accompanied by the mobility increase of not gapped carriers due to the suppression of electron-electron scattering. SmFeAs(O0.93F0.07) exhibits an increase of the metallic character on cooling consistent with electron doping, even though at room temperature values of all the properties nearly overlaps with those of SmFeAsO. However, with temperature decrease all anomalies related to the SDW instability are missed and the superconducting transition occurs. This suggests that doping breaks abruptly the symmetries of the Fermi surface inhibiting the SDW formation in favor of the superconducting transition, with no substantial changes in the density of states or in the effective mass.