Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA.
Phys Rev Lett. 2023 Mar 3;130(9):096901. doi: 10.1103/PhysRevLett.130.096901.
The ac conduction of epitaxially grown SmB_{6} thin films and superconducting heterostructures of SmB_{6}/YB_{6} are investigated via time-domain terahertz spectroscopy. A two-channel model of thickness-dependent bulk states and thickness-independent surface states accurately describes the measured conductance of bare SmB_{6} thin films, demonstrating the presence of surface states in SmB_{6}. While the observed reductions in the simultaneously measured superconducting gap, transition temperature, and superfluid density of SmB_{6}/YB_{6} heterostructures relative to bare YB_{6} indicate the penetration of proximity-induced superconductivity into the SmB_{6} overlayer; the corresponding SmB_{6}-thickness independence between different heterostructures indicates that the induced superconductivity is predominantly confined to the interface surface state of the SmB_{6}. This study demonstrates the ability of terahertz spectroscopy to probe proximity-induced superconductivity at an interface buried within a heterostructure, and our results show that SmB_{6} behaves as a predominantly insulating bulk surrounded by conducting surface states in both the normal and induced-superconducting states in both terahertz and dc responses, which is consistent with the topological Kondo insulator picture.
通过时域太赫兹光谱研究了外延生长的 SmB_{6} 薄膜和 SmB_{6}/YB_{6} 超导异质结构的 ac 输运性质。一个厚度相关的体态和厚度独立的表面态的双通道模型准确地描述了裸 SmB_{6} 薄膜的测量电导，证明了 SmB_{6} 中存在表面态。虽然观察到 SmB_{6}/YB_{6} 异质结构的超导能隙、转变温度和超流密度相对于裸 YB_{6} 同时减小，表明近邻诱导超导性穿透到 SmB_{6} 覆盖层中；不同异质结构之间相应的 SmB_{6} 厚度独立性表明，诱导超导主要局限于 SmB_{6} 的界面表面态。这项研究证明了太赫兹光谱在异质结构内探测界面近邻诱导超导的能力，我们的结果表明，SmB_{6} 在太赫兹和直流响应的正常和诱导超导状态下都表现为主要是绝缘的体，周围是导电的表面态，这与拓扑 Kondo 绝缘体能隙图一致。
