1] Brookhaven National Laboratory, Upton, New York 11973-5000, USA [2] National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA.
Nat Mater. 2013 Oct;12(10):877-81. doi: 10.1038/nmat3719. Epub 2013 Aug 4.
The recent discovery of superconductivity at the interface of two non-superconducting materials has received much attention. In cuprate bilayers, the critical temperature (Tc) can be significantly enhanced compared with single-phase samples. Several explanations have been proposed, invoking Sr interdiffusion, accumulation and depletion of mobile charge carriers, elongation of the copper-to-apical-oxygen bond length, or a beneficial crosstalk between a material with a high pairing energy and another with a large phase stiffness. From each of these models, one would predict Tc to depend strongly on the carrier density in the constituent materials. Here, we study combinatorial libraries of La(2-x)Sr(x)CuO4-La2CuO4 bilayer samples--an unprecedentedly large set of more than 800 different compositions. The doping level x spans a wide range, 0.15 < x < 0.47, and the measured Hall coefficient varies by one order of magnitude. Nevertheless, across the entire sample set, Tc stays essentially constant at about 40 K. We infer that doping up to the optimum level does not shift the chemical potential, unlike in ordinary Fermi liquids. This result poses a new challenge to theory--cuprate superconductors have not run out of surprises.
最近在两种非超导材料的界面发现超导性引起了广泛关注。在铜酸盐双层中，与单相样品相比，临界温度 (Tc) 可以显著提高。已经提出了几种解释，涉及 Sr 互扩散、可移动载流子的积累和耗尽、铜-顶氧键长的延长，或者高配对能材料与大相刚度材料之间的有益串扰。从这些模型中的每一个，人们都会预测 Tc 强烈依赖于组成材料中的载流子密度。在这里，我们研究了 La(2-x)Sr(x)CuO4-La2CuO4 双层样品的组合库——这是一个前所未有的超过 800 种不同成分的大型集合。掺杂水平 x 跨越很宽的范围，0.15 < x < 0.47，测量的霍尔系数变化了一个数量级。然而，在整个样品集中，Tc 基本上保持在约 40 K 不变。我们推断，与普通费米液体不同，掺杂到最佳水平不会改变化学势。这一结果对理论提出了新的挑战——铜酸盐超导体还有更多的惊喜。
