Superconductivity in fluoride-arsenide SrLa_xFeAsF compounds

National Laboratory for Superconductivity, Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences - P. O. Box 603, Beijing 100190, PRC

Corresponding author: hhwen@aphy.iphy.ac.cn

Received: 17 November 2008
Accepted: 8 December 2008

Abstract

By using a two-step solid-state reaction method, we successfully fabricated the new family of fluoride-arsenide AeFeAsF compounds (Ae = alkaline-earth elements, Sr, Eu and Ca) with the ZrCuSiAs structure and with the new building block AeF instead of the REO (both the formal charge of the AeF Layer and the REO layer are “+1"). The undoped parent phase has a Spin-Density-Wave–like transition at about 173 K for SrFeAsF, 118 K for CaFeAsF and 153 K for EuFeAsF. By doping electrons into the system the resistivity anomaly associated with this SDW transition is suppressed and superconductivity appears at 29.5 K (with the criterion of 90% of the normal-state resistivity) in the fluoride-arsenide SrLa_xFeAsF (x = 0.4). Our discovery here suggests that other new superconductors may be obtained if one uses different rare-earth elements to substitute the alkaline-earth elements in AeFeAsF.