标题： 在掺杂超导拓扑绝缘体（基于Bi2Se3类）中观察到拓扑序 显示英文标题

标题： Observation of topological order in a Superconducting doped topological insulator (based on the Bi2Se3 class)

摘要： 拓扑绝缘体代表了一种新的物质状态，其完全由体电子结构的拓扑不变量来表征，而不是任何自发对称性破缺的形式。 与二维量子霍尔或类似量子自旋霍尔的系统不同，三维（3D）拓扑绝缘体可以容纳磁性和超导性，这在凝聚态物理和材料物理界引发了广泛的研究活动。 因此，人们对理解拓扑态与对称性破缺态（如超导性）之间的丰富相互作用产生了爆炸式的兴趣，这一兴趣极大地受到一些提议的推动，这些提议认为将超导性引入某些能带结构中将产生具有量子信息科学意义的奇异准粒子。 掺杂Bi_2Se_3（Cu$_x$Bi$_2$Se$_3$）和掺杂Bi_2Te_3（Pd$_x$-Bi$_2$Te$_3$ T$_c$ $\sim$ 5K）中的超导性观测引发了关于这些三元复合物自旋-轨道物理的许多引人入胜的问题，而任何严格的超导理论仍然难以捉摸。 此处我们提供了在系统可调的正常态下铜$_x$铋$_2$硒$_3$（x=0到12%）中电子动力学的关键测量结果，从而深入了解其自旋-轨道行为以及在低温下发生超导性的表面拓扑性质。 我们的数据表明，超导性发生在（样品组成中）电子处于体相对论运动状态的情况下，并且我们确定一种非常规掺杂机制使得未掺杂化合物的拓扑表面特性在超导化合物的费米能级上得以保持，在那里库珀对在低温下形成。 这些实验观察结果为发展三维拓扑绝缘体中拓扑超导性的理论提供了重要线索。 显示英文摘要

摘要： Topological insulators embody a new state of matter characterized entirely by the topological invariants of the bulk electronic structure rather than any form of spontaneously broken symmetry. Unlike the 2D quantum Hall or quantum spin-Hall-like systems, the three dimensional (3D) topological insulators can host magnetism and superconductivity which has generated widespread research activity in condensed-matter and materials-physics communities. Thus there is an explosion of interest in understanding the rich interplay between topological and the broken-symmetry states (such as superconductivity), greatly spurred by proposals that superconductivity introduced into certain band structures will host exotic quasiparticles which are of interest in quantum information science. The observations of superconductivity in doped Bi_2Se_3 (Cu$_x$Bi$_2$Se$_3$) and doped Bi_2Te_3 (Pd$_x$-Bi$_2$Te$_3$ T$_c$ $\sim$ 5K) have raised many intriguing questions about the spin-orbit physics of these ternary complexes while any rigorous theory of superconductivity remains elusive. Here we present key measurements of electron dynamics in systematically tunable normal state of Cu$_x$Bi$_2$Se$_3$ (x=0 to 12%) gaining insights into its spin-orbit behavior and the topological nature of the surface where superconductivity takes place at low temperatures. Our data reveal that superconductivity occurs (in sample compositions) with electrons in a bulk relativistic kinematic regime and we identify that an unconventional doping mechanism causes the topological surface character of the undoped compound to be preserved at the Fermi level of the superconducting compound, where Cooper pairing occurs at low temperatures. These experimental observations provide important clues for developing a theory of topological-superconductivity in 3D topological insulators.