Neupane Madhab, Ishida Yukiaki, Sankar Raman, Zhu Jian-Xin, Sanchez Daniel S, Belopolski Ilya, Xu Su-Yang, Alidoust Nasser, Hosen M Mofazzel, Shin Shik, Chou Fangcheng, Hasan M Zahid, Durakiewicz Tomasz
Condensed Matter and Magnet Science Group, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
Department of Physics, University of Central Florida, Orlando, Florida 32816, USA.
Sci Rep. 2016 Mar 3;6:22557. doi: 10.1038/srep22557.
Topological superconductors host new states of quantum matter which show a pairing gap in the bulk and gapless surface states providing a platform to realize Majorana fermions. Recently, alkaline-earth metal Sr intercalated Bi2Se3 has been reported to show superconductivity with a Tc ~ 3 K and a large shielding fraction. Here we report systematic normal state electronic structure studies of Sr0.06Bi2Se3 (Tc ~ 2.5 K) by performing photoemission spectroscopy. Using angle-resolved photoemission spectroscopy (ARPES), we observe a quantum well confined two-dimensional (2D) state coexisting with a topological surface state in Sr0.06Bi2Se3. Furthermore, our time-resolved ARPES reveals the relaxation dynamics showing different decay mechanism between the excited topological surface states and the two-dimensional states. Our experimental observation is understood by considering the intra-band scattering for topological surface states and an additional electron phonon scattering for the 2D states, which is responsible for the superconductivity. Our first-principles calculations agree with the more effective scattering and a shorter lifetime of the 2D states. Our results will be helpful in understanding low temperature superconducting states of these topological materials.
拓扑超导体承载着新的量子物质态，其体内存在配对能隙，表面态无隙，为实现马约拉纳费米子提供了一个平台。最近，有报道称碱土金属锶插层的Bi2Se3呈现出超导性，其临界温度Tc约为3 K，屏蔽分数较大。在此，我们通过光电子能谱对Sr0.06Bi2Se3（Tc约为2.5 K）进行了系统的正常态电子结构研究。利用角分辨光电子能谱（ARPES），我们观察到在Sr0.06Bi2Se3中，量子阱限制的二维（2D）态与拓扑表面态共存。此外，我们的时间分辨ARPES揭示了弛豫动力学，表明激发的拓扑表面态和二维态之间存在不同的衰减机制。通过考虑拓扑表面态的带内散射和二维态的额外电子-声子散射来理解我们的实验观测结果，后者与超导性有关。我们的第一性原理计算与二维态更有效的散射和更短的寿命相一致。我们的结果将有助于理解这些拓扑材料的低温超导态。
