Brookhaven National Laboratory, Upton, NY 11973, USA.
Quantum Condensed Matter Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
Sci Rep. 2017 Apr 5;7:45896. doi: 10.1038/srep45896.
In copper-oxides that show high-temperature superconductivity (HTS), the critical temperature (T) has a dome-shaped doping dependence. The cause of demise of both T and superfluid density n on the overdoped side is a major puzzle. A recent study of transport and diamagnetism in a large number of overdoped LaSrCuO (LSCO) films shows that this cannot be accounted for by disorder within the conventional Bardeen-Cooper-Schrieffer theory. This brings to focus an alternative explanation - competition of HTS with ferromagnetic order, fluctuating in superconducting samples and static beyond the superconductor-to-metal transition. Here, we examine this proposal by growing single-crystal LSCO thin films with doping on both sides of the transition by molecular beam epitaxy, and using polarized neutron reflectometry to measure their magnetic moments. In a heavily overdoped, metallic but non-superconducting LSCO (x = 0.35) film, the spin asymmetry of reflectivity shows a very small static magnetic moment (~2 emu/cm). Less-doped, superconducting LSCO films show no magnetic moment in neutron reflectivity, both above and below T. Therefore, the collapse of HTS with overdoping is not caused by competing ferromagnetic order.
在具有高温超导性（HTS）的铜氧化物中，临界温度（T）具有穹顶形掺杂依赖性。在过掺杂侧，T 和超流密度 n 的消失的原因是一个主要的难题。最近对大量过掺杂 LaSrCuO（LSCO）薄膜的输运和抗磁性的研究表明，这不能用传统的 Bardeen-Cooper-Schrieffer 理论中的无序来解释。这将焦点转移到另一种解释上 - HTS 与铁磁有序的竞争，在超导样品中波动，在超导到金属转变之外则是静态的。在这里，我们通过分子束外延在转变的两侧生长单晶 LSCO 薄膜，并使用极化中子反射测量其磁矩，来检验这一建议。在一个过掺杂、金属但非超导的 LSCO（x=0.35）薄膜中，反射率的自旋不对称性显示出一个非常小的静态磁矩（约 2 emu/cm）。在中子反射率中，掺杂较少的超导 LSCO 薄膜在 T 以上和以下都没有磁矩。因此，过掺杂时 HTS 的崩溃不是由竞争的铁磁有序引起的。
