Thermal properties of SmFeAsO 1 − x F x as a probe of the interplay between electrons and phonons

A comparative study of thermal properties of SmFeAsO, $\text{SmFeAs}({\text{O}}_{0.93}{\text{F}}_{0.07})$, and $\text{SmFeAs}({\text{O}}_{0.85}{\text{F}}_{0.15})$ samples is presented. Specific heat and thermal conductivity show clear evidence of the spin-density wave (SDW) ordering below ${T}_{\text{SDW}}\ensuremath{\sim}135\text{ }\text{K}$ in undoped SmFeAsO. At low level of F doping, $\text{SmFeAs}({\text{O}}_{0.93}{\text{F}}_{0.07})$, SDW ordering is suppressed and superconducting features are not yet optimally developed in both specific heat and thermal conductivity. At optimal level of F-doping $\text{SmFeAs}({\text{O}}_{0.85}{\text{F}}_{0.15})$ anomalies related to the superconducting transition are well noticeable. By a compared analysis of doped and undoped samples we conclude that despite the fact that F doping modifies definitely the electronic ground state, it does not substantially alter phonon and electron parameters, such as phonon modes, Sommerfeld coefficient, and electro-phonon coupling. The analysis of the thermal conductivity curves provides an evaluation of the SDW and superconducting energy gap, showing that phonons can suitably probe features of the electronic ground state.