Evidence for s-wave pairing with atomic scale disorder in the van der Waals superconductor NaSn2As2
Evidence for s-wave pairing with atomic scale disorder in the van der Waals superconductor NaSn2As2
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DOI：
10.1103/physrevb.98.020503
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发表时间：
2018-07-13
影响因子：
3.7
通讯作者：
Shibauchi, T.
中科院分区：
文献类型：
--
作者：
Ishihara, K.;Takenaka, T.;Shibauchi, T.
最近发现的具有范德华层状结构的NaSn2As2的超导性对其配对机制和潜在的电子结构提出了直接的问题。在这里，我们给出了温度相关的磁穿透深度λ (T)在NaSn2As2单晶中的测量值，低至类似于40 mK。我们发现一个非常长的穿透深度λ (0) = 960 nm，这比第一原理计算的估计值强得多。这种增强来自于一个接近1.7 nm的短平均自由程，这表明原子尺度上的无序可能与Sn的跳价态有关。超流体密度的温度依赖性与脏极限下常规的全间隙s波状态完全一致。这些结果表明，NaSn2As2具有可控的维数，是研究强无序超导体量子相涨落的理想材料。
The recent discovery of superconductivity in NaSn2As2 with a van der Waals layered structure raises immediate questions on its pairing mechanism and underlying electronic structure. Here, we present measurements of the temperature-dependent magnetic penetration depth lambda(T) in single crystals of NaSn2As2 down to similar to 40 mK. We find a very long penetration depth lambda(0) = 960 nm, which is strongly enhanced from the estimate of first-principles calculations. This enhancement comes from a short mean free path l approximate to 1.7 nm, indicating atomic scale disorder possibly associated with the valence-skipping states of Sn. The temperature dependence of superfluid density is fully consistent with the conventional fully gapped s-wave state in the dirty limit. These results suggest that NaSn2As2 is an ideal material to study quantum phase fluctuations in strongly disordered superconductors with its controllable dimensionality.