Department of Physics, Kyoto University, Kyoto 606-8502, Japan.
Max-Planck Institute for Chemical Physics of Solids, D-01187 Dresden, Germany.
Phys Rev Lett. 2018 Oct 12;121(15):157004. doi: 10.1103/PhysRevLett.121.157004.
Nuclear magnetic resonance measurements were performed on CeCu_{2}Si_{2} in the presence of a magnetic field close to the upper critical field μ_{0}H_{c2} in order to investigate its superconducting (SC) properties near pair-breaking fields. In lower fields, the Knight shift and nuclear spin-lattice relaxation rate divided by temperature 1/T_{1}T abruptly decreased below the SC transition temperature T_{c}(H), a phenomenon understood within the framework of conventional spin-singlet superconductivity. In contrast, 1/T_{1}T was enhanced just below T_{c}(H) and exhibited a broad maximum when magnetic fields close to μ_{0}H_{c2}(0) were applied parallel or perpendicular to the c axis; although the Knight shift decreased just below T_{c}(H). This enhancement of 1/T_{1}T, which was recently observed in the organic superconductor κ-(BEDT-TTF){2}Cu(NCS){2}, suggests the presence of high-density Andreev bound states in the inhomogeneous SC region, a hallmark of the Fulde-Ferrell-Larkin-Ovchinnikov phase.
在接近上临界磁场μ0Hc2 的磁场存在下，对 CeCu2Si2 进行了核磁共振测量，以研究其在对超导（SC）性质有破坏作用的磁场附近的超导（SC）性质。在较低的磁场中，Knight 位移和核自旋晶格弛豫率与温度的比值 1/T1T 在超导转变温度 Tc(H)以下突然下降，这种现象在传统的单自旋超导理论框架内可以得到解释。相比之下，当磁场平行或垂直于 c 轴施加到接近μ0Hc2(0)时，1/T1T 在 Tc(H)以下就会增强，并表现出一个宽的最大值；尽管 Knight 位移在 Tc(H)以下下降。这种 1/T1T 的增强最近在有机超导体 κ-(BEDT-TTF)2Cu(NCS)2 中被观察到，表明在非均匀 SC 区域中存在高密度的 Andreev 束缚态，这是 Fulde-Ferrell-Larkin-Ovchinnikov 相的标志。
