SrFeAsF as a parent compound for iron pnictide superconductors

Abstract

We have successfully synthesized the fluo-arsenide SrFeAsF, a new parent phase with the ZrCuSiAs structure. The temperature dependence of resistivity and dc magnetization both reveal an anomaly at about Tan = 173 K, which may correspond to the structural and/or Spin-Density-Wave (SDW) transition. Strong Hall effect and moderate magnetoresistance were observed below Tan. Interestingly, the Hall coefficient RH is positive below Tan, 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)Fe2As2 where the Hall coefficient RH is negative. This strongly suggests that the gapping of the Fermi surface induced by the SDW order leaves one of the hole pockets fully or partially ungapped in SrFeAsF. Our data show that it is possible for the parent phases of the arsenide superconductors to display dominant carriers that are either electronlike or holelike.PACS numbers: 74.70. Dd, 74.25.Fy, 75.30.Fv, 74.10.+v The discovery of superconductivity in the quaternary compound LaFeAsO 1−x F x which is abbreviated as the FeAs-1111 phase, has attracted great attentions in the fields of condensed matter physics and material sciences.1 The family of the FeAs-based superconductors has been extended rapidly. As for the FeAs-1111 phase, most of the discovered superconductors are characterized as electron-doped ones and the superconducting transition temperature has been quickly raised to T c = 55∼ 56 K via replacing lanthanum with other rare earth elements. 2,3,4,5,6,7 Meanwhile, the first holedoped superconductor La 1−x Sr x FeAsO with T c ≈ 25 K was discovered, 8,9 followed with the observation of superconductivity in hole-doped Nd 1−x Sr x FeAsO 10 and Pr 1−x Sr x FeAsO.11 Later on, (Ba, Sr) 1−x K x Fe 2 As 2 which is denoted as FeAs-122 for simplicity 12,13,14 , and Li x FeAs as an infinite layered structure (denoted as FeAs-111) were discovered. 15,16,17 It is assumed that the superconductivity both in the FeAs-1111 phase and FeAs-122 phase is intimately connected with a Spin-DensityWave (SDW) anomaly in the FeAs layers.12,18 For undoped LaFeAsO, an SDW-driven structural phase transition around 150 K was found.19 It seems that any new parent phase will initiate a series of new superconductors by doping it away from the state with features of a bad metal and the SDW order.In this paper, we report the discovery of a new FeAsbased layered compound SrFeAsF which has the ZrCuSiAs structure. As we know SrZnPF is a compound with the ZrCuSiAs structure 20 . We replace the ZnP sheets with FeAs sheets and get a new compound of SrFeAsF. The compound SrFeAsF has the tetragonal space group P4/nmm at 300 K. Both the resistivity and the dc magnetic susceptibility exhibit a clear anomaly at about 173 K, which is attributed to the structural and/or SDW transition. Surprisingly, a positive Hall coefficient R H has been found implying a dominant conduction by holelike charge carriers in this parent phase.The SrFeAsF samples were prepared using a two-step solid s...

Sr3Sc2Fe2As2O5as

“…1,13,20,22 The skeleton shown in the right hand side of Fig.1 gives the structure model of our sample. It is clear that the Fe ions construct a square lattice and the FeAs-layer stacks with the (Sr 3 Sc 2 O 5 ) building block along c-axis.…”

“…Superconductivity at about 2.2 K has also been found in a NiP-based layered structure La 3 Ni 4 O 2 P 4 with the inter growth of NiP-1111 and 122 building blocks. 12 Very recently, another kind of parent compounds (Sr,Ca,Eu)FeAsF were reported, 13,14,15,16 which may lead to high temperature superconductors by doping charges into the system.…”

Discovery of a novel 112-type iron-pnictide and La-doping induced superconductivity in Eu 1− x La x FeAs 2 ( x = 0–0.15)

“…Since the first report of high-T c superconductivity in LaFeAs(O,F) at 26 K in 2008, hundreds of new layered iron pnictide superconductors have been discovered, with all of them formed by the typical Fe 2 As 2 layers stacking with various types of blocking layers [1][2][3][4][5][6][7][8][9][10]. Among them, the 1111-type SmFeAs(O,F) still holds the highest T c around 55 K in bulk materials after 8 years [11].…”

New Layered Fluorosulfide SrFBiS2

“…Therefore, the replacement of LaO by SrF should not change the band structure and thus physical properties too much, especially at low temperature, similar to the relation between SrFFeAs and LaOFeAs. 18,31 The slight differences between LaOBiS 2 and SrFBiS 2 , such as larger a-axial and smaller c-axial lattice parameters, could result in changing of physical properties at higher temperature. Note that the semiconducting ρ(T ) in LaOBiS 2 and SrFBiS 2 are different from those in parent compounds of iron pnictide superconductors.…”