Lee Jinwon, Lee Sanghun, Kreisel Andreas, Paaske Jens, Andersen Brian M, Bastiaans Koen M, Chatzopoulos Damianos, Gu Genda, Cho Doohee, Allan Milan P
Leiden Institute of Physics, Leiden University, Leiden 2333CA, The Netherlands.
Department of Physics, Yonsei University, Seoul 03722, Republic of Korea.
Nano Lett. 2025 Mar 19;25(11):4227-4233. doi: 10.1021/acs.nanolett.4c05650. Epub 2025 Feb 12.
The iron-based superconductor FeTeSe is a peculiar material: it hosts surface states with a Dirac dispersion, is a putative topological superconductor hosting Majorana modes in vortices, and has an unusually low Fermi energy. The superconducting state is generally characterized by three gaps in different bands, with the homogeneous, spatially extended Bogoliubov excitations─in this work, we uncover evidence that it is instead of a very different nature. Our scanning tunneling spectroscopy data show several peaks in the density of states above a full gap, and by analyzing their spatial and junction-resistance dependence, we conclude the peaks above the first one are not coherence peaks from different bands. Instead, comparisons with our simulations indicate they originate from generalized Shiba states that are spatially overlapping. This can lead to an amorphous state of Bogoliubov quasiparticles, reminiscent of impurity bands in semiconductors. We discuss the origin and implications of this new state.
铁基超导体FeTeSe是一种特殊的材料：它具有狄拉克色散的表面态，是一种在涡旋中存在马约拉纳模式的假定拓扑超导体，并且具有异常低的费米能。超导态通常由不同能带中的三个能隙表征，具有均匀的、空间扩展的博戈留波夫激发——在这项工作中，我们发现证据表明它具有截然不同的性质。我们的扫描隧道谱数据显示，在完全能隙之上的态密度中有几个峰，通过分析它们对空间和结电阻的依赖性，我们得出结论，第一个峰之上的峰不是来自不同能带的相干峰。相反，与我们的模拟结果比较表明，它们起源于空间重叠的广义志波态。这可能导致博戈留波夫准粒子的非晶态，让人联想到半导体中的杂质带。我们讨论了这种新状态的起源和意义。
