A topological insulator film coupled to a simple isotropic s-wave superconductor substrate can foster helical pairing of the Dirac fermions associated with the topological surface states. Experimental realization of such a system is exceedingly difficult, however using a novel “flip-chip” technique, we have prepared single-crystalline Bi2Se3 films with predetermined thicknesses in terms of quintuple layers (QLs) on top of Nb substrates fresh from in situ cleavage. Our angle-resolved photoemission spectroscopy (ARPES) measurements of the film surface disclose superconducting gaps and coherence peaks of similar magnitude for both the topological surface states and bulk states. The ARPES spectral map as a function of temperature and film thickness up to 10 QLs reveals key characteristics relevant to the mechanism of coupling between the topological surface states and the superconducting Nb substrate; the effective coupling length is found to be much larger than the decay length of the topological surface states.
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机译：耦合到简单的各向同性s波超导体衬底的拓扑绝缘膜可以促进与拓扑表面状态相关的狄拉克费米子的螺旋配对。这种系统的实验实现极其困难，但是使用一种新颖的“倒装芯片”技术，我们制备了具有预定厚度的单晶Bi 2 Se 3 薄膜。原位裂解的Nb基质顶部的五重层（QLs）术语。我们对薄膜表面的角度分辨光发射光谱（ARPES）测量结果显示，对于拓扑表面状态和本体状态，超导间隙和相干峰的大小相似。 ARPES光谱图作为温度和薄膜厚度（最多10个QL）的函数，揭示了与拓扑表面态与超导Nb衬底之间的耦合机制有关的关键特性;发现有效耦合长度远大于拓扑表面状态的衰减长度。
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