Mn在LaFe（1-x）Mn（x）AsO（0.89）F（0.11）中的中毒效应：揭示铁基超导体phase diagram中的量子临界点
The poisoning effect of Mn in LaFe(1-x)Mn(x)AsO(0.89)F(0.11): unveiling a quantum critical point in the phase diagram of iron-based superconductors
摘要：
报道了LaFe $_{1-x}$ Mn $_x$ AsO $_{0.89}$ F $_{0.11}$的超导-磁转变，其中千分之一的Mn杂质分散。通过对Mn含量从x=0.025%到x= 0.75%的化合物采用μ子自旋旋转（muSR）和核四极共振（NQR）等局域光谱技术，我们发现Mn杂质对化合物的电子性质非常敏感。事实上，低至0.2%的少量Mn完全抑制超导电性。静态磁性，涉及的FeAs平面，观察到出现x > 0.1%，并成为进一步增强后，增加Mn取代。此外，低能自旋涨落的逐步增加，导致NQR自旋-晶格弛豫速率1/T1的增强，观察到Mn取代后。对最接近超导性和磁性之间的交叉（x = 0.2%）的样品的1/T1的分析指向在该掺杂水平附近存在反铁磁量子临界点。
英文摘要：
A superconducting-to-magnetic transition is reported for LaFe$_{1-x}$Mn$_x$AsO$_{0.89}$F$_{0.11}$ where a per thousand amount of Mn impurities is dispersed. By employing local spectroscopic techniques like muon spin rotation (muSR) and nuclear quadrupole resonance (NQR) on compounds with Mn contents ranging from x=0.025% to x=0.75%, we find that the electronic properties are extremely sensitive to the Mn impurities. In fact, a small amount of Mn as low as 0.2% suppresses superconductivity completely. Static magnetism, involving the FeAs planes, is observed to arise for x > 0.1% and becomes further enhanced upon increasing Mn substitution. Also a progressive increase of low energy spin fluctuations, leading to an enhancement of the NQR spin-lattice relaxation rate 1/T1, is observed upon Mn substitution. The analysis of 1/T1 for the sample closest to the the crossover between superconductivity and magnetism (x = 0.2%) points towards the presence of an antiferromagnetic quantum critical point around that doping level.
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