Two-fold symmetric superconductivity in few-layer NbSe2
Two-fold symmetric superconductivity in few-layer NbSe2
复制标题
少层NbSe2的双对称超导性
DOI：
10.1038/s41567-021-01219-x
复制
发表时间：
2021-04-15
期刊：
影响因子：
19.6
通讯作者：
Pribiag, Vlad S.
中科院分区：
文献类型：
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作者：
Hamill, Alex;Heischmidt, Brett;Pribiag, Vlad S.
某些二维过渡金属二硫族化合物的强伊辛自旋-轨道耦合可以深刻地影响少数层样品的超导态。例如，在NbSe2中，这种效应与降维相结合，在高达35 T的磁场下稳定超导状态，并可能导致拓扑超导。在这里，我们报道了在平面外磁场作用下，与晶格的三重对称性相反，在少层NbSe2中超导态具有双重旋转对称性。在NbSe2/CrBr3超导-磁体隧道结中，磁电阻和临界场均表现出这种双重对称性，并且在超导态深处也表现出这种对称性。在这两种情况下，各向异性在正常状态下消失，表明它是超导相的固有性质。我们将这种行为归因于两种紧密竞争的配对不稳定性之间的混合，即块状NbSe2中典型的常规s波不稳定性和在少数层NbSe2中出现的非常规d或p波通道。我们的研究结果证明了在少层过渡金属二硫族化合物中配对相互作用的非常规特征，并突出了这类二维材料中的奇异超导性。
The strong Ising spin-orbit coupling in certain two-dimensional transition metal dichalcogenides can profoundly affect the superconducting state in few-layer samples. For example, in NbSe2, this effect combines with the reduced dimensionality to stabilize the superconducting state against magnetic fields up to similar to 35 T, and could lead to topological superconductivity. Here we report a two-fold rotational symmetry of the superconducting state in few-layer NbSe2 under in-plane external magnetic fields, in contrast to the three-fold symmetry of the lattice. Both the magnetoresistance and critical field exhibit this two-fold symmetry, and it also manifests deep inside the superconducting state in NbSe2/CrBr3 superconductor-magnet tunnel junctions. In both cases, the anisotropy vanishes in the normal state, demonstrating that it is an intrinsic property of the superconducting phase. We attribute the behaviour to the mixing between two closely competing pairing instabilities, namely the conventional s-wave instability typical of bulk NbSe2 and an unconventional d- or p-wave channel that emerges in few-layer NbSe2. Our results demonstrate the unconventional character of the pairing interaction in few-layer transition metal dichalcogenides and highlight the exotic superconductivity in this family of two-dimensional materials.