Determination of New Magnetic Structures in LaFeAs1-xPxO

LaFeAs1-xPxO has recently been proposed to display unusual properties as a function of P doping with two distinct superconducting (SC) domes separated by a possible AFM phase as suggested by NMR spectroscopy. Initial neutron diffraction data obtained over this composition range (0.4 < x < 0.7) failed to reveal the existence of long range magnetic order between the SC domes. The absence of any obvious physical ground state is difficult to understand especially in a range where superconductivity is clearly suppressed without any apparent driving force! Recently, we performed preliminary proof-of-principle measurements using muon spin rotation at EMU and neutron diffraction (long data collection time) on WISH and successfully proved the existence of at least two magnetic phases at different P contents. Careful measurements are needed on WISH, HRPD and EMU as described in the proposal.

近期有研究提出，LaFeAs₁₋ₓPₓO的反常物性随磷(P)掺杂量变化呈现出两个独立的超导（SC, Superconducting）穹顶，且两超导穹顶之间可能存在反铁磁（AFM, Antiferromagnetic）相，该结论得到核磁共振（NMR, Nuclear Magnetic Resonance）光谱学的佐证。针对组分范围0.4 < x < 0.7的初始中子衍射数据，未能观测到超导穹顶间存在长程磁有序。在超导性被显著抑制却无明显驱动因素的组分区间内，未发现明确物理基态的现象尤其难以阐释。近期，我们依托EMU装置开展了μ子自旋旋转的原理验证初步实验，并在WISH装置上完成了长采集时长的中子衍射测试，成功证实了不同P掺杂量下至少存在两种磁相。如本提案所述，需在WISH、HRPD及EMU装置上开展精细化测量工作。