SrFeAsF as a parent compound for iron pnictide superconductors

TL;DR

This study reports the synthesis and characterization of SrFeAsF, a new parent compound for iron pnictide superconductors, revealing unique electronic properties and a complex SDW transition that challenges previous assumptions.

Contribution

The paper introduces SrFeAsF as a novel parent phase with distinct Hall effect behavior, expanding understanding of electronic structures in iron pnictide systems.

Findings

Anomaly at 173 K indicating a structural/SDW transition

Positive Hall coefficient below T_{an}, opposite to known parent phases

Evidence of complex Fermi surface gapping and variable charge carriers

Abstract

We have successfully synthesized the fluo-arsenide SrFeAsF, a new parent phase with the ZrCuAsSi structure. The temperature dependence of resistivity and dc magnetization both reveal an anomaly at about T_{an} = 173 K, which may correspond to the structural and/or Spin-Density-Wave (SDW) transition. Strong Hall effect and magnetoresistance were observed below T_{an}. Interestingly, the Hall coefficient R_H is positive below T_{an}, which is opposite to the cases in the two parent phases of FeAs-based systems known so far, i.e., LnFeAsO (Ln = rare earth elements) and (Ba, Sr)Fe_2As_2 where the Hall coefficient R_H is negative. This strongly suggests that the gapping to the Fermi surfaces induced by the SDW order is more complex than we believed before that it removes the density of states on some Fermi pockets and leaves one of the electron pockets less-gapped or un-gapped. Our data clearly show that it is possible for the parent phase to have electron-like or hole-like charge carriers.